perf(router-core): guard default search parser against throws

[anonrig]

What

Stop the default search parser from throwing a SyntaxError for every plain-string param. In packages/router-core/src/searchParams.ts, defaultParseSearch ran JSON.parse on every leftover string value:

-export const defaultParseSearch = parseSearchWith(JSON.parse)+export const defaultParseSearch = parseSearchWith(parseMaybeJson)

parseMaybeJson first checks, from the first non-whitespace character, whether the value could be JSON and only then calls JSON.parse. The check is a superset of JSON's value-start grammar ({ [ " -0-9t f n, skipping leading whitespace), so any string JSON.parse would accept still gets parsed — we only skip the doomed parse of plain strings.

Why

qss.decode already coerces numbers/booleans, so JSON.parse only ever runs on the remaining string values — which on real apps are mostly plain text (?q=hello&f=live&src=typed_query). Each one throws a SyntaxError that parseSearchWith catches to keep the raw string, and constructing + throwing that error (with stack capture) is the dominant cost.

Search params are parsed on every SSR request and every client navigation. In-situ before/after on the real defaultParseSearch (Vitest bench):

Query shape	old (JSON.parse)	new (guarded)	Speedup
mixed X-like (?q=…&f=live&src=…&pf=1)	317K ops/s	996K ops/s	3.1×
all plain strings (?q=from:elon since:2024&f=live&…)	107K ops/s	176K ops/s	1.7×

Correctness

Behavior is identical. The guard never skips a value JSON.parse would accept, and for skipped values it returns the raw string — exactly what parseSearchWith does today when JSON.parse throws.

Verified by:

• The full existing searchParams suite (isomorphism round-trips + "alien deserialization" of human-typed params).
• A 5000+ case fuzz confirming couldBeJson is a correct superset of JSON.parse's accept set.
• Four added tests: plain-string params stay strings, leading-whitespace JSON values still parse (guard skips whitespace), JSON-looking-but-invalid values fall back to the raw string, and t/f/n-prefixed non-literals (tweet, false_alarm, null_island) stay strings.

nx run @tanstack/router-core:test:unit -> 1182 passed (+ 3 expected-fail)
nx run @tanstack/router-core:test:types -> no errors

Notes

• Only the default parse path changes. defaultStringifySearch uses the same JSON.parse-as-throw-probe pattern when building URLs (also hot via <Link>), but its logic relies on throw-vs-no-throw as the "is this JSON?" signal, so making it allocation-free cleanly is a slightly larger change — happy to do it as a follow-up.
• Includes a changeset (@tanstack/router-core patch).
• Pre-existing unused-imports/no-unused-vars warnings on the existing catch (_err) blocks are untouched by this change.

Summary by CodeRabbit

• Performance
  • Optimized query parameter parsing to reduce processing overhead, improving performance for server-side rendering and client-side navigation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 81d1c0ab-ecfc-4d71-a1b9-8028d3b188c0

📥 Commits

Reviewing files that changed from the base of the PR and between 279a849 and b4a3303.

📒 Files selected for processing (3)

• .changeset/perf-default-search-parse-guard.md
• packages/router-core/src/searchParams.ts
• packages/router-core/tests/searchParams.test.ts

---

📝 Walkthrough

Walkthrough

Adds two internal helpers (couldBeJson and parseMaybeJson) to searchParams.ts. couldBeJson checks the first non-whitespace character to determine if a string could be a valid JSON value; parseMaybeJson calls JSON.parse only when that check passes. defaultParseSearch is updated to use parseMaybeJson instead of JSON.parse directly. New tests and a changeset accompany the change.

Changes

defaultParseSearch JSON parse guard

Layer / File(s)

Summary

couldBeJson / parseMaybeJson helpers and defaultParseSearch wiring packages/router-core/src/searchParams.ts, packages/router-core/tests/searchParams.test.ts, .changeset/perf-default-search-parse-guard.md

couldBeJson scans past leading whitespace and checks the first character against valid JSON-start characters. parseMaybeJson wraps JSON.parse behind that guard, returning the raw string when the check fails. defaultParseSearch is switched from parseSearchWith(JSON.parse) to parseSearchWith(parseMaybeJson). Tests cover plain strings, leading-whitespace JSON, invalid JSON-looking inputs, and non-literal t/f/n-prefixed words. The changeset documents the performance motivation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related issues

• defaultParseSearch corrupts string search params that look like JSON numbers (e.g. "662E41", large integers) — lossy and unrecoverable on inbound URLs #7650 — Both this PR and that issue modify defaultParseSearch in searchParams.ts to add a guard before JSON.parse; the issue specifically targets precision-loss coercion of hex strings like "662E41" to numbers, which is a distinct case the first-character heuristic here does not address (hex strings start with a digit 6, which couldBeJson would pass).

Suggested labels

package: router-core

Suggested reviewers

• chorobin

Poem

🐇 Hop hop, no parse for thee,
A string that starts with h runs free!
No more throw/catch on every quest,
couldBeJson guards the nest.
Less overhead, more speedy ways—
The router hops through query haze! 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'perf(router-core): guard default search parser against throws' directly and specifically describes the main change—adding a guard to prevent expensive JSON.parse throws in the default search parser, which is the core optimization in this PR.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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---

☁️ Nx Cloud last updated this comment at 2026-06-22 13:53:24 UTC

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commit: b4a3303

[codspeed-hq]

Merging this PR will degrade performance by 11.83%

❌ 3 regressed benchmarks
✅ 141 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	mem serialization-payload (vue)	6.8 MB	8.7 MB	-22.2%
❌	Memory	mem aborted-requests (vue)	959.1 KB	1,048.9 KB	-8.56%
❌	Memory	mem request-churn (vue)	1.3 MB	1.3 MB	-3.66%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing anonrig:perf/default-search-parse-guard (b4a3303) with main (f23ed0f)¹}

Footnotes

1. No successful run was found on main (279a849) during the generation of this report, so f23ed0f was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[nx-cloud]

Nx Cloud has identified a possible root cause for your failed CI:

We classified this failure as an environment state issue rather than a code change. The error — a missing resolveRuntimeSuffix export in e2e/e2e-utils/dist/esm/index.js — points to stale or inconsistently built dist artifacts in the e2e test infrastructure, which has no relation to the @tanstack/router-core search param optimization introduced by this PR. Rebuilding the e2e-utils package should restore consistent artifacts and resolve the failure.

No code changes were suggested for this issue.

You can trigger a rerun by pushing an empty commit:

git commit --allow-empty -m "chore: trigger rerun"
git push

View detailed reasoning on Nx Cloud ↗

_{🎓 Learn more about Self-Healing CI on nx.dev}

[anonrig]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

[Sheraff]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

I already had a pretty similar PR a while ago https://github.com/TanStack/router/pull/5071/changes

not sure why we never merged it.

[anonrig]

What

Stop the default search parser from throwing a SyntaxError for every plain-string param. In packages/router-core/src/searchParams.ts, defaultParseSearch ran JSON.parse on every leftover string value:

-export const defaultParseSearch = parseSearchWith(JSON.parse)+export const defaultParseSearch = parseSearchWith(parseMaybeJson)

parseMaybeJson first checks, from the first non-whitespace character, whether the value could be JSON and only then calls JSON.parse. The check is a superset of JSON's value-start grammar ({ [ " -0-9t f n, skipping leading whitespace), so any string JSON.parse would accept still gets parsed — we only skip the doomed parse of plain strings.

Why

qss.decode already coerces numbers/booleans, so JSON.parse only ever runs on the remaining string values — which on real apps are mostly plain text (?q=hello&f=live&src=typed_query). Each one throws a SyntaxError that parseSearchWith catches to keep the raw string, and constructing + throwing that error (with stack capture) is the dominant cost.

Search params are parsed on every SSR request and every client navigation. In-situ before/after on the real defaultParseSearch (Vitest bench):

Query shape	old (JSON.parse)	new (guarded)	Speedup
mixed X-like (?q=…&f=live&src=…&pf=1)	317K ops/s	996K ops/s	3.1×
all plain strings (?q=from:elon since:2024&f=live&…)	107K ops/s	176K ops/s	1.7×

Correctness

Behavior is identical. The guard never skips a value JSON.parse would accept, and for skipped values it returns the raw string — exactly what parseSearchWith does today when JSON.parse throws.

Verified by:

• The full existing searchParams suite (isomorphism round-trips + "alien deserialization" of human-typed params).
• A 5000+ case fuzz confirming couldBeJson is a correct superset of JSON.parse's accept set.
• Four added tests: plain-string params stay strings, leading-whitespace JSON values still parse (guard skips whitespace), JSON-looking-but-invalid values fall back to the raw string, and t/f/n-prefixed non-literals (tweet, false_alarm, null_island) stay strings.

nx run @tanstack/router-core:test:unit -> 1182 passed (+ 3 expected-fail)
nx run @tanstack/router-core:test:types -> no errors

Notes

• Only the default parse path changes. defaultStringifySearch uses the same JSON.parse-as-throw-probe pattern when building URLs (also hot via <Link>), but its logic relies on throw-vs-no-throw as the "is this JSON?" signal, so making it allocation-free cleanly is a slightly larger change — happy to do it as a follow-up.
• Includes a changeset (@tanstack/router-core patch).
• Pre-existing unused-imports/no-unused-vars warnings on the existing catch (_err) blocks are untouched by this change.

Summary by CodeRabbit

• Performance
  • Optimized query parameter parsing to reduce processing overhead, improving performance for server-side rendering and client-side navigation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 81d1c0ab-ecfc-4d71-a1b9-8028d3b188c0

📥 Commits

Reviewing files that changed from the base of the PR and between 279a849 and b4a3303.

📒 Files selected for processing (3)

• .changeset/perf-default-search-parse-guard.md
• packages/router-core/src/searchParams.ts
• packages/router-core/tests/searchParams.test.ts

---

📝 Walkthrough

Walkthrough

Adds two internal helpers (couldBeJson and parseMaybeJson) to searchParams.ts. couldBeJson checks the first non-whitespace character to determine if a string could be a valid JSON value; parseMaybeJson calls JSON.parse only when that check passes. defaultParseSearch is updated to use parseMaybeJson instead of JSON.parse directly. New tests and a changeset accompany the change.

Changes

defaultParseSearch JSON parse guard

Layer / File(s)

Summary

couldBeJson / parseMaybeJson helpers and defaultParseSearch wiring packages/router-core/src/searchParams.ts, packages/router-core/tests/searchParams.test.ts, .changeset/perf-default-search-parse-guard.md

couldBeJson scans past leading whitespace and checks the first character against valid JSON-start characters. parseMaybeJson wraps JSON.parse behind that guard, returning the raw string when the check fails. defaultParseSearch is switched from parseSearchWith(JSON.parse) to parseSearchWith(parseMaybeJson). Tests cover plain strings, leading-whitespace JSON, invalid JSON-looking inputs, and non-literal t/f/n-prefixed words. The changeset documents the performance motivation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related issues

• defaultParseSearch corrupts string search params that look like JSON numbers (e.g. "662E41", large integers) — lossy and unrecoverable on inbound URLs #7650 — Both this PR and that issue modify defaultParseSearch in searchParams.ts to add a guard before JSON.parse; the issue specifically targets precision-loss coercion of hex strings like "662E41" to numbers, which is a distinct case the first-character heuristic here does not address (hex strings start with a digit 6, which couldBeJson would pass).

Suggested labels

package: router-core

Suggested reviewers

• chorobin

Poem

🐇 Hop hop, no parse for thee,
A string that starts with h runs free!
No more throw/catch on every quest,
couldBeJson guards the nest.
Less overhead, more speedy ways—
The router hops through query haze! 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'perf(router-core): guard default search parser against throws' directly and specifically describes the main change—adding a guard to prevent expensive JSON.parse throws in the default search parser, which is the core optimization in this PR.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Command	Status	Duration	Result
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---

☁️ Nx Cloud last updated this comment at 2026-06-22 13:53:24 UTC

[pkg-pr-new]

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commit: b4a3303

[codspeed-hq]

Merging this PR will degrade performance by 11.83%

❌ 3 regressed benchmarks
✅ 141 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	mem serialization-payload (vue)	6.8 MB	8.7 MB	-22.2%
❌	Memory	mem aborted-requests (vue)	959.1 KB	1,048.9 KB	-8.56%
❌	Memory	mem request-churn (vue)	1.3 MB	1.3 MB	-3.66%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing anonrig:perf/default-search-parse-guard (b4a3303) with main (f23ed0f)¹}

Footnotes

1. No successful run was found on main (279a849) during the generation of this report, so f23ed0f was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[nx-cloud]

Nx Cloud has identified a possible root cause for your failed CI:

We classified this failure as an environment state issue rather than a code change. The error — a missing resolveRuntimeSuffix export in e2e/e2e-utils/dist/esm/index.js — points to stale or inconsistently built dist artifacts in the e2e test infrastructure, which has no relation to the @tanstack/router-core search param optimization introduced by this PR. Rebuilding the e2e-utils package should restore consistent artifacts and resolve the failure.

No code changes were suggested for this issue.

You can trigger a rerun by pushing an empty commit:

git commit --allow-empty -m "chore: trigger rerun"
git push

View detailed reasoning on Nx Cloud ↗

_{🎓 Learn more about Self-Healing CI on nx.dev}

[anonrig]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

[Sheraff]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

I already had a pretty similar PR a while ago https://github.com/TanStack/router/pull/5071/changes

not sure why we never merged it.

[anonrig]

What

Stop the default search parser from throwing a SyntaxError for every plain-string param. In packages/router-core/src/searchParams.ts, defaultParseSearch ran JSON.parse on every leftover string value:

-export const defaultParseSearch = parseSearchWith(JSON.parse)+export const defaultParseSearch = parseSearchWith(parseMaybeJson)

parseMaybeJson first checks, from the first non-whitespace character, whether the value could be JSON and only then calls JSON.parse. The check is a superset of JSON's value-start grammar ({ [ " -0-9t f n, skipping leading whitespace), so any string JSON.parse would accept still gets parsed — we only skip the doomed parse of plain strings.

Why

qss.decode already coerces numbers/booleans, so JSON.parse only ever runs on the remaining string values — which on real apps are mostly plain text (?q=hello&f=live&src=typed_query). Each one throws a SyntaxError that parseSearchWith catches to keep the raw string, and constructing + throwing that error (with stack capture) is the dominant cost.

Search params are parsed on every SSR request and every client navigation. In-situ before/after on the real defaultParseSearch (Vitest bench):

Query shape	old (JSON.parse)	new (guarded)	Speedup
mixed X-like (?q=…&f=live&src=…&pf=1)	317K ops/s	996K ops/s	3.1×
all plain strings (?q=from:elon since:2024&f=live&…)	107K ops/s	176K ops/s	1.7×

Correctness

Behavior is identical. The guard never skips a value JSON.parse would accept, and for skipped values it returns the raw string — exactly what parseSearchWith does today when JSON.parse throws.

Verified by:

• The full existing searchParams suite (isomorphism round-trips + "alien deserialization" of human-typed params).
• A 5000+ case fuzz confirming couldBeJson is a correct superset of JSON.parse's accept set.
• Four added tests: plain-string params stay strings, leading-whitespace JSON values still parse (guard skips whitespace), JSON-looking-but-invalid values fall back to the raw string, and t/f/n-prefixed non-literals (tweet, false_alarm, null_island) stay strings.

nx run @tanstack/router-core:test:unit -> 1182 passed (+ 3 expected-fail)
nx run @tanstack/router-core:test:types -> no errors

Notes

• Only the default parse path changes. defaultStringifySearch uses the same JSON.parse-as-throw-probe pattern when building URLs (also hot via <Link>), but its logic relies on throw-vs-no-throw as the "is this JSON?" signal, so making it allocation-free cleanly is a slightly larger change — happy to do it as a follow-up.
• Includes a changeset (@tanstack/router-core patch).
• Pre-existing unused-imports/no-unused-vars warnings on the existing catch (_err) blocks are untouched by this change.

Summary by CodeRabbit

• Performance
  • Optimized query parameter parsing to reduce processing overhead, improving performance for server-side rendering and client-side navigation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 81d1c0ab-ecfc-4d71-a1b9-8028d3b188c0

📥 Commits

Reviewing files that changed from the base of the PR and between 279a849 and b4a3303.

📒 Files selected for processing (3)

• .changeset/perf-default-search-parse-guard.md
• packages/router-core/src/searchParams.ts
• packages/router-core/tests/searchParams.test.ts

---

📝 Walkthrough

Walkthrough

Adds two internal helpers (couldBeJson and parseMaybeJson) to searchParams.ts. couldBeJson checks the first non-whitespace character to determine if a string could be a valid JSON value; parseMaybeJson calls JSON.parse only when that check passes. defaultParseSearch is updated to use parseMaybeJson instead of JSON.parse directly. New tests and a changeset accompany the change.

Changes

defaultParseSearch JSON parse guard

Layer / File(s)

Summary

couldBeJson / parseMaybeJson helpers and defaultParseSearch wiring packages/router-core/src/searchParams.ts, packages/router-core/tests/searchParams.test.ts, .changeset/perf-default-search-parse-guard.md

couldBeJson scans past leading whitespace and checks the first character against valid JSON-start characters. parseMaybeJson wraps JSON.parse behind that guard, returning the raw string when the check fails. defaultParseSearch is switched from parseSearchWith(JSON.parse) to parseSearchWith(parseMaybeJson). Tests cover plain strings, leading-whitespace JSON, invalid JSON-looking inputs, and non-literal t/f/n-prefixed words. The changeset documents the performance motivation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related issues

• defaultParseSearch corrupts string search params that look like JSON numbers (e.g. "662E41", large integers) — lossy and unrecoverable on inbound URLs #7650 — Both this PR and that issue modify defaultParseSearch in searchParams.ts to add a guard before JSON.parse; the issue specifically targets precision-loss coercion of hex strings like "662E41" to numbers, which is a distinct case the first-character heuristic here does not address (hex strings start with a digit 6, which couldBeJson would pass).

Suggested labels

package: router-core

Suggested reviewers

• chorobin

Poem

🐇 Hop hop, no parse for thee,
A string that starts with h runs free!
No more throw/catch on every quest,
couldBeJson guards the nest.
Less overhead, more speedy ways—
The router hops through query haze! 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'perf(router-core): guard default search parser against throws' directly and specifically describes the main change—adding a guard to prevent expensive JSON.parse throws in the default search parser, which is the core optimization in this PR.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[nx-cloud]

View your CI Pipeline Execution ↗ for commit b4a3303

Command	Status	Duration	Result
nx affected --targets=test:eslint,test:unit,tes...	❌ Failed	22m 33s	View ↗
nx run-many --target=build --exclude=examples/*...	✅ Succeeded	2m 17s	View ↗

---

☁️ Nx Cloud last updated this comment at 2026-06-22 13:53:24 UTC

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commit: b4a3303

[codspeed-hq]

Merging this PR will degrade performance by 11.83%

❌ 3 regressed benchmarks
✅ 141 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	mem serialization-payload (vue)	6.8 MB	8.7 MB	-22.2%
❌	Memory	mem aborted-requests (vue)	959.1 KB	1,048.9 KB	-8.56%
❌	Memory	mem request-churn (vue)	1.3 MB	1.3 MB	-3.66%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing anonrig:perf/default-search-parse-guard (b4a3303) with main (f23ed0f)¹}

Footnotes

1. No successful run was found on main (279a849) during the generation of this report, so f23ed0f was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[nx-cloud]

Nx Cloud has identified a possible root cause for your failed CI:

We classified this failure as an environment state issue rather than a code change. The error — a missing resolveRuntimeSuffix export in e2e/e2e-utils/dist/esm/index.js — points to stale or inconsistently built dist artifacts in the e2e test infrastructure, which has no relation to the @tanstack/router-core search param optimization introduced by this PR. Rebuilding the e2e-utils package should restore consistent artifacts and resolve the failure.

No code changes were suggested for this issue.

You can trigger a rerun by pushing an empty commit:

git commit --allow-empty -m "chore: trigger rerun"
git push

View detailed reasoning on Nx Cloud ↗

_{🎓 Learn more about Self-Healing CI on nx.dev}

[anonrig]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

[Sheraff]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

I already had a pretty similar PR a while ago https://github.com/TanStack/router/pull/5071/changes

not sure why we never merged it.

[anonrig]

What

Stop the default search parser from throwing a SyntaxError for every plain-string param. In packages/router-core/src/searchParams.ts, defaultParseSearch ran JSON.parse on every leftover string value:

-export const defaultParseSearch = parseSearchWith(JSON.parse)+export const defaultParseSearch = parseSearchWith(parseMaybeJson)

parseMaybeJson first checks, from the first non-whitespace character, whether the value could be JSON and only then calls JSON.parse. The check is a superset of JSON's value-start grammar ({ [ " -0-9t f n, skipping leading whitespace), so any string JSON.parse would accept still gets parsed — we only skip the doomed parse of plain strings.

Why

qss.decode already coerces numbers/booleans, so JSON.parse only ever runs on the remaining string values — which on real apps are mostly plain text (?q=hello&f=live&src=typed_query). Each one throws a SyntaxError that parseSearchWith catches to keep the raw string, and constructing + throwing that error (with stack capture) is the dominant cost.

Search params are parsed on every SSR request and every client navigation. In-situ before/after on the real defaultParseSearch (Vitest bench):

Query shape	old (JSON.parse)	new (guarded)	Speedup
mixed X-like (?q=…&f=live&src=…&pf=1)	317K ops/s	996K ops/s	3.1×
all plain strings (?q=from:elon since:2024&f=live&…)	107K ops/s	176K ops/s	1.7×

Correctness

Behavior is identical. The guard never skips a value JSON.parse would accept, and for skipped values it returns the raw string — exactly what parseSearchWith does today when JSON.parse throws.

Verified by:

• The full existing searchParams suite (isomorphism round-trips + "alien deserialization" of human-typed params).
• A 5000+ case fuzz confirming couldBeJson is a correct superset of JSON.parse's accept set.
• Four added tests: plain-string params stay strings, leading-whitespace JSON values still parse (guard skips whitespace), JSON-looking-but-invalid values fall back to the raw string, and t/f/n-prefixed non-literals (tweet, false_alarm, null_island) stay strings.

nx run @tanstack/router-core:test:unit -> 1182 passed (+ 3 expected-fail)
nx run @tanstack/router-core:test:types -> no errors

Notes

• Only the default parse path changes. defaultStringifySearch uses the same JSON.parse-as-throw-probe pattern when building URLs (also hot via <Link>), but its logic relies on throw-vs-no-throw as the "is this JSON?" signal, so making it allocation-free cleanly is a slightly larger change — happy to do it as a follow-up.
• Includes a changeset (@tanstack/router-core patch).
• Pre-existing unused-imports/no-unused-vars warnings on the existing catch (_err) blocks are untouched by this change.

Summary by CodeRabbit

• Performance
  • Optimized query parameter parsing to reduce processing overhead, improving performance for server-side rendering and client-side navigation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 81d1c0ab-ecfc-4d71-a1b9-8028d3b188c0

📥 Commits

Reviewing files that changed from the base of the PR and between 279a849 and b4a3303.

📒 Files selected for processing (3)

• .changeset/perf-default-search-parse-guard.md
• packages/router-core/src/searchParams.ts
• packages/router-core/tests/searchParams.test.ts

---

📝 Walkthrough

Walkthrough

Adds two internal helpers (couldBeJson and parseMaybeJson) to searchParams.ts. couldBeJson checks the first non-whitespace character to determine if a string could be a valid JSON value; parseMaybeJson calls JSON.parse only when that check passes. defaultParseSearch is updated to use parseMaybeJson instead of JSON.parse directly. New tests and a changeset accompany the change.

Changes

defaultParseSearch JSON parse guard

Layer / File(s)

Summary

couldBeJson / parseMaybeJson helpers and defaultParseSearch wiring packages/router-core/src/searchParams.ts, packages/router-core/tests/searchParams.test.ts, .changeset/perf-default-search-parse-guard.md

couldBeJson scans past leading whitespace and checks the first character against valid JSON-start characters. parseMaybeJson wraps JSON.parse behind that guard, returning the raw string when the check fails. defaultParseSearch is switched from parseSearchWith(JSON.parse) to parseSearchWith(parseMaybeJson). Tests cover plain strings, leading-whitespace JSON, invalid JSON-looking inputs, and non-literal t/f/n-prefixed words. The changeset documents the performance motivation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related issues

• defaultParseSearch corrupts string search params that look like JSON numbers (e.g. "662E41", large integers) — lossy and unrecoverable on inbound URLs #7650 — Both this PR and that issue modify defaultParseSearch in searchParams.ts to add a guard before JSON.parse; the issue specifically targets precision-loss coercion of hex strings like "662E41" to numbers, which is a distinct case the first-character heuristic here does not address (hex strings start with a digit 6, which couldBeJson would pass).

Suggested labels

package: router-core

Suggested reviewers

• chorobin

Poem

🐇 Hop hop, no parse for thee,
A string that starts with h runs free!
No more throw/catch on every quest,
couldBeJson guards the nest.
Less overhead, more speedy ways—
The router hops through query haze! 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'perf(router-core): guard default search parser against throws' directly and specifically describes the main change—adding a guard to prevent expensive JSON.parse throws in the default search parser, which is the core optimization in this PR.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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🧪 Generate unit tests (beta)

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[nx-cloud]

View your CI Pipeline Execution ↗ for commit b4a3303

Command	Status	Duration	Result
nx affected --targets=test:eslint,test:unit,tes...	❌ Failed	22m 33s	View ↗
nx run-many --target=build --exclude=examples/*...	✅ Succeeded	2m 17s	View ↗

---

☁️ Nx Cloud last updated this comment at 2026-06-22 13:53:24 UTC

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commit: b4a3303

[codspeed-hq]

Merging this PR will degrade performance by 11.83%

❌ 3 regressed benchmarks
✅ 141 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	mem serialization-payload (vue)	6.8 MB	8.7 MB	-22.2%
❌	Memory	mem aborted-requests (vue)	959.1 KB	1,048.9 KB	-8.56%
❌	Memory	mem request-churn (vue)	1.3 MB	1.3 MB	-3.66%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing anonrig:perf/default-search-parse-guard (b4a3303) with main (f23ed0f)¹}

Footnotes

1. No successful run was found on main (279a849) during the generation of this report, so f23ed0f was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[nx-cloud]

Nx Cloud has identified a possible root cause for your failed CI:

We classified this failure as an environment state issue rather than a code change. The error — a missing resolveRuntimeSuffix export in e2e/e2e-utils/dist/esm/index.js — points to stale or inconsistently built dist artifacts in the e2e test infrastructure, which has no relation to the @tanstack/router-core search param optimization introduced by this PR. Rebuilding the e2e-utils package should restore consistent artifacts and resolve the failure.

No code changes were suggested for this issue.

You can trigger a rerun by pushing an empty commit:

git commit --allow-empty -m "chore: trigger rerun"
git push

View detailed reasoning on Nx Cloud ↗

_{🎓 Learn more about Self-Healing CI on nx.dev}

[anonrig]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

[Sheraff]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

I already had a pretty similar PR a while ago https://github.com/TanStack/router/pull/5071/changes

not sure why we never merged it.

[anonrig]

What

Stop the default search parser from throwing a SyntaxError for every plain-string param. In packages/router-core/src/searchParams.ts, defaultParseSearch ran JSON.parse on every leftover string value:

-export const defaultParseSearch = parseSearchWith(JSON.parse)+export const defaultParseSearch = parseSearchWith(parseMaybeJson)

parseMaybeJson first checks, from the first non-whitespace character, whether the value could be JSON and only then calls JSON.parse. The check is a superset of JSON's value-start grammar ({ [ " -0-9t f n, skipping leading whitespace), so any string JSON.parse would accept still gets parsed — we only skip the doomed parse of plain strings.

Why

qss.decode already coerces numbers/booleans, so JSON.parse only ever runs on the remaining string values — which on real apps are mostly plain text (?q=hello&f=live&src=typed_query). Each one throws a SyntaxError that parseSearchWith catches to keep the raw string, and constructing + throwing that error (with stack capture) is the dominant cost.

Search params are parsed on every SSR request and every client navigation. In-situ before/after on the real defaultParseSearch (Vitest bench):

Query shape	old (JSON.parse)	new (guarded)	Speedup
mixed X-like (?q=…&f=live&src=…&pf=1)	317K ops/s	996K ops/s	3.1×
all plain strings (?q=from:elon since:2024&f=live&…)	107K ops/s	176K ops/s	1.7×

Correctness

Behavior is identical. The guard never skips a value JSON.parse would accept, and for skipped values it returns the raw string — exactly what parseSearchWith does today when JSON.parse throws.

Verified by:

• The full existing searchParams suite (isomorphism round-trips + "alien deserialization" of human-typed params).
• A 5000+ case fuzz confirming couldBeJson is a correct superset of JSON.parse's accept set.
• Four added tests: plain-string params stay strings, leading-whitespace JSON values still parse (guard skips whitespace), JSON-looking-but-invalid values fall back to the raw string, and t/f/n-prefixed non-literals (tweet, false_alarm, null_island) stay strings.

nx run @tanstack/router-core:test:unit -> 1182 passed (+ 3 expected-fail)
nx run @tanstack/router-core:test:types -> no errors

Notes

• Only the default parse path changes. defaultStringifySearch uses the same JSON.parse-as-throw-probe pattern when building URLs (also hot via <Link>), but its logic relies on throw-vs-no-throw as the "is this JSON?" signal, so making it allocation-free cleanly is a slightly larger change — happy to do it as a follow-up.
• Includes a changeset (@tanstack/router-core patch).
• Pre-existing unused-imports/no-unused-vars warnings on the existing catch (_err) blocks are untouched by this change.

Summary by CodeRabbit

• Performance
  • Optimized query parameter parsing to reduce processing overhead, improving performance for server-side rendering and client-side navigation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

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Run ID: 81d1c0ab-ecfc-4d71-a1b9-8028d3b188c0

📥 Commits

Reviewing files that changed from the base of the PR and between 279a849 and b4a3303.

📒 Files selected for processing (3)

• .changeset/perf-default-search-parse-guard.md
• packages/router-core/src/searchParams.ts
• packages/router-core/tests/searchParams.test.ts

---

📝 Walkthrough

Walkthrough

Adds two internal helpers (couldBeJson and parseMaybeJson) to searchParams.ts. couldBeJson checks the first non-whitespace character to determine if a string could be a valid JSON value; parseMaybeJson calls JSON.parse only when that check passes. defaultParseSearch is updated to use parseMaybeJson instead of JSON.parse directly. New tests and a changeset accompany the change.

Changes

defaultParseSearch JSON parse guard

Layer / File(s)

Summary

couldBeJson / parseMaybeJson helpers and defaultParseSearch wiring packages/router-core/src/searchParams.ts, packages/router-core/tests/searchParams.test.ts, .changeset/perf-default-search-parse-guard.md

couldBeJson scans past leading whitespace and checks the first character against valid JSON-start characters. parseMaybeJson wraps JSON.parse behind that guard, returning the raw string when the check fails. defaultParseSearch is switched from parseSearchWith(JSON.parse) to parseSearchWith(parseMaybeJson). Tests cover plain strings, leading-whitespace JSON, invalid JSON-looking inputs, and non-literal t/f/n-prefixed words. The changeset documents the performance motivation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related issues

• defaultParseSearch corrupts string search params that look like JSON numbers (e.g. "662E41", large integers) — lossy and unrecoverable on inbound URLs #7650 — Both this PR and that issue modify defaultParseSearch in searchParams.ts to add a guard before JSON.parse; the issue specifically targets precision-loss coercion of hex strings like "662E41" to numbers, which is a distinct case the first-character heuristic here does not address (hex strings start with a digit 6, which couldBeJson would pass).

Suggested labels

package: router-core

Suggested reviewers

• chorobin

Poem

🐇 Hop hop, no parse for thee,
A string that starts with h runs free!
No more throw/catch on every quest,
couldBeJson guards the nest.
Less overhead, more speedy ways—
The router hops through query haze! 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'perf(router-core): guard default search parser against throws' directly and specifically describes the main change—adding a guard to prevent expensive JSON.parse throws in the default search parser, which is the core optimization in this PR.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[nx-cloud]

View your CI Pipeline Execution ↗ for commit b4a3303

Command	Status	Duration	Result
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---

☁️ Nx Cloud last updated this comment at 2026-06-22 13:53:24 UTC

[pkg-pr-new]

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commit: b4a3303

[codspeed-hq]

Merging this PR will degrade performance by 11.83%

❌ 3 regressed benchmarks
✅ 141 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	mem serialization-payload (vue)	6.8 MB	8.7 MB	-22.2%
❌	Memory	mem aborted-requests (vue)	959.1 KB	1,048.9 KB	-8.56%
❌	Memory	mem request-churn (vue)	1.3 MB	1.3 MB	-3.66%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing anonrig:perf/default-search-parse-guard (b4a3303) with main (f23ed0f)¹}

Footnotes

1. No successful run was found on main (279a849) during the generation of this report, so f23ed0f was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[nx-cloud]

Nx Cloud has identified a possible root cause for your failed CI:

We classified this failure as an environment state issue rather than a code change. The error — a missing resolveRuntimeSuffix export in e2e/e2e-utils/dist/esm/index.js — points to stale or inconsistently built dist artifacts in the e2e test infrastructure, which has no relation to the @tanstack/router-core search param optimization introduced by this PR. Rebuilding the e2e-utils package should restore consistent artifacts and resolve the failure.

No code changes were suggested for this issue.

You can trigger a rerun by pushing an empty commit:

git commit --allow-empty -m "chore: trigger rerun"
git push

View detailed reasoning on Nx Cloud ↗

_{🎓 Learn more about Self-Healing CI on nx.dev}

[anonrig]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

[Sheraff]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

I already had a pretty similar PR a while ago https://github.com/TanStack/router/pull/5071/changes

not sure why we never merged it.

[anonrig]

What

Stop the default search parser from throwing a SyntaxError for every plain-string param. In packages/router-core/src/searchParams.ts, defaultParseSearch ran JSON.parse on every leftover string value:

-export const defaultParseSearch = parseSearchWith(JSON.parse)+export const defaultParseSearch = parseSearchWith(parseMaybeJson)

parseMaybeJson first checks, from the first non-whitespace character, whether the value could be JSON and only then calls JSON.parse. The check is a superset of JSON's value-start grammar ({ [ " -0-9t f n, skipping leading whitespace), so any string JSON.parse would accept still gets parsed — we only skip the doomed parse of plain strings.

Why

qss.decode already coerces numbers/booleans, so JSON.parse only ever runs on the remaining string values — which on real apps are mostly plain text (?q=hello&f=live&src=typed_query). Each one throws a SyntaxError that parseSearchWith catches to keep the raw string, and constructing + throwing that error (with stack capture) is the dominant cost.

Search params are parsed on every SSR request and every client navigation. In-situ before/after on the real defaultParseSearch (Vitest bench):

Query shape	old (JSON.parse)	new (guarded)	Speedup
mixed X-like (?q=…&f=live&src=…&pf=1)	317K ops/s	996K ops/s	3.1×
all plain strings (?q=from:elon since:2024&f=live&…)	107K ops/s	176K ops/s	1.7×

Correctness

Behavior is identical. The guard never skips a value JSON.parse would accept, and for skipped values it returns the raw string — exactly what parseSearchWith does today when JSON.parse throws.

Verified by:

• The full existing searchParams suite (isomorphism round-trips + "alien deserialization" of human-typed params).
• A 5000+ case fuzz confirming couldBeJson is a correct superset of JSON.parse's accept set.
• Four added tests: plain-string params stay strings, leading-whitespace JSON values still parse (guard skips whitespace), JSON-looking-but-invalid values fall back to the raw string, and t/f/n-prefixed non-literals (tweet, false_alarm, null_island) stay strings.

nx run @tanstack/router-core:test:unit -> 1182 passed (+ 3 expected-fail)
nx run @tanstack/router-core:test:types -> no errors

Notes

• Only the default parse path changes. defaultStringifySearch uses the same JSON.parse-as-throw-probe pattern when building URLs (also hot via <Link>), but its logic relies on throw-vs-no-throw as the "is this JSON?" signal, so making it allocation-free cleanly is a slightly larger change — happy to do it as a follow-up.
• Includes a changeset (@tanstack/router-core patch).
• Pre-existing unused-imports/no-unused-vars warnings on the existing catch (_err) blocks are untouched by this change.

Summary by CodeRabbit

• Performance
  • Optimized query parameter parsing to reduce processing overhead, improving performance for server-side rendering and client-side navigation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 81d1c0ab-ecfc-4d71-a1b9-8028d3b188c0

📥 Commits

Reviewing files that changed from the base of the PR and between 279a849 and b4a3303.

📒 Files selected for processing (3)

• .changeset/perf-default-search-parse-guard.md
• packages/router-core/src/searchParams.ts
• packages/router-core/tests/searchParams.test.ts

---

📝 Walkthrough

Walkthrough

Adds two internal helpers (couldBeJson and parseMaybeJson) to searchParams.ts. couldBeJson checks the first non-whitespace character to determine if a string could be a valid JSON value; parseMaybeJson calls JSON.parse only when that check passes. defaultParseSearch is updated to use parseMaybeJson instead of JSON.parse directly. New tests and a changeset accompany the change.

Changes

defaultParseSearch JSON parse guard

Layer / File(s)

Summary

couldBeJson / parseMaybeJson helpers and defaultParseSearch wiring packages/router-core/src/searchParams.ts, packages/router-core/tests/searchParams.test.ts, .changeset/perf-default-search-parse-guard.md

couldBeJson scans past leading whitespace and checks the first character against valid JSON-start characters. parseMaybeJson wraps JSON.parse behind that guard, returning the raw string when the check fails. defaultParseSearch is switched from parseSearchWith(JSON.parse) to parseSearchWith(parseMaybeJson). Tests cover plain strings, leading-whitespace JSON, invalid JSON-looking inputs, and non-literal t/f/n-prefixed words. The changeset documents the performance motivation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related issues

• defaultParseSearch corrupts string search params that look like JSON numbers (e.g. "662E41", large integers) — lossy and unrecoverable on inbound URLs #7650 — Both this PR and that issue modify defaultParseSearch in searchParams.ts to add a guard before JSON.parse; the issue specifically targets precision-loss coercion of hex strings like "662E41" to numbers, which is a distinct case the first-character heuristic here does not address (hex strings start with a digit 6, which couldBeJson would pass).

Suggested labels

package: router-core

Suggested reviewers

• chorobin

Poem

🐇 Hop hop, no parse for thee,
A string that starts with h runs free!
No more throw/catch on every quest,
couldBeJson guards the nest.
Less overhead, more speedy ways—
The router hops through query haze! 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'perf(router-core): guard default search parser against throws' directly and specifically describes the main change—adding a guard to prevent expensive JSON.parse throws in the default search parser, which is the core optimization in this PR.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Command	Status	Duration	Result
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---

☁️ Nx Cloud last updated this comment at 2026-06-22 13:53:24 UTC

[pkg-pr-new]

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commit: b4a3303

[codspeed-hq]

Merging this PR will degrade performance by 11.83%

❌ 3 regressed benchmarks
✅ 141 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	mem serialization-payload (vue)	6.8 MB	8.7 MB	-22.2%
❌	Memory	mem aborted-requests (vue)	959.1 KB	1,048.9 KB	-8.56%
❌	Memory	mem request-churn (vue)	1.3 MB	1.3 MB	-3.66%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing anonrig:perf/default-search-parse-guard (b4a3303) with main (f23ed0f)¹}

Footnotes

1. No successful run was found on main (279a849) during the generation of this report, so f23ed0f was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[nx-cloud]

Nx Cloud has identified a possible root cause for your failed CI:

We classified this failure as an environment state issue rather than a code change. The error — a missing resolveRuntimeSuffix export in e2e/e2e-utils/dist/esm/index.js — points to stale or inconsistently built dist artifacts in the e2e test infrastructure, which has no relation to the @tanstack/router-core search param optimization introduced by this PR. Rebuilding the e2e-utils package should restore consistent artifacts and resolve the failure.

No code changes were suggested for this issue.

You can trigger a rerun by pushing an empty commit:

git commit --allow-empty -m "chore: trigger rerun"
git push

View detailed reasoning on Nx Cloud ↗

_{🎓 Learn more about Self-Healing CI on nx.dev}

[anonrig]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

[Sheraff]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

I already had a pretty similar PR a while ago https://github.com/TanStack/router/pull/5071/changes

not sure why we never merged it.

[anonrig]

What

Stop the default search parser from throwing a SyntaxError for every plain-string param. In packages/router-core/src/searchParams.ts, defaultParseSearch ran JSON.parse on every leftover string value:

-export const defaultParseSearch = parseSearchWith(JSON.parse)+export const defaultParseSearch = parseSearchWith(parseMaybeJson)

parseMaybeJson first checks, from the first non-whitespace character, whether the value could be JSON and only then calls JSON.parse. The check is a superset of JSON's value-start grammar ({ [ " -0-9t f n, skipping leading whitespace), so any string JSON.parse would accept still gets parsed — we only skip the doomed parse of plain strings.

Why

qss.decode already coerces numbers/booleans, so JSON.parse only ever runs on the remaining string values — which on real apps are mostly plain text (?q=hello&f=live&src=typed_query). Each one throws a SyntaxError that parseSearchWith catches to keep the raw string, and constructing + throwing that error (with stack capture) is the dominant cost.

Search params are parsed on every SSR request and every client navigation. In-situ before/after on the real defaultParseSearch (Vitest bench):

Query shape	old (JSON.parse)	new (guarded)	Speedup
mixed X-like (?q=…&f=live&src=…&pf=1)	317K ops/s	996K ops/s	3.1×
all plain strings (?q=from:elon since:2024&f=live&…)	107K ops/s	176K ops/s	1.7×

Correctness

Behavior is identical. The guard never skips a value JSON.parse would accept, and for skipped values it returns the raw string — exactly what parseSearchWith does today when JSON.parse throws.

Verified by:

• The full existing searchParams suite (isomorphism round-trips + "alien deserialization" of human-typed params).
• A 5000+ case fuzz confirming couldBeJson is a correct superset of JSON.parse's accept set.
• Four added tests: plain-string params stay strings, leading-whitespace JSON values still parse (guard skips whitespace), JSON-looking-but-invalid values fall back to the raw string, and t/f/n-prefixed non-literals (tweet, false_alarm, null_island) stay strings.

nx run @tanstack/router-core:test:unit -> 1182 passed (+ 3 expected-fail)
nx run @tanstack/router-core:test:types -> no errors

Notes

• Only the default parse path changes. defaultStringifySearch uses the same JSON.parse-as-throw-probe pattern when building URLs (also hot via <Link>), but its logic relies on throw-vs-no-throw as the "is this JSON?" signal, so making it allocation-free cleanly is a slightly larger change — happy to do it as a follow-up.
• Includes a changeset (@tanstack/router-core patch).
• Pre-existing unused-imports/no-unused-vars warnings on the existing catch (_err) blocks are untouched by this change.

Summary by CodeRabbit

• Performance
  • Optimized query parameter parsing to reduce processing overhead, improving performance for server-side rendering and client-side navigation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 81d1c0ab-ecfc-4d71-a1b9-8028d3b188c0

📥 Commits

Reviewing files that changed from the base of the PR and between 279a849 and b4a3303.

📒 Files selected for processing (3)

• .changeset/perf-default-search-parse-guard.md
• packages/router-core/src/searchParams.ts
• packages/router-core/tests/searchParams.test.ts

---

📝 Walkthrough

Walkthrough

Adds two internal helpers (couldBeJson and parseMaybeJson) to searchParams.ts. couldBeJson checks the first non-whitespace character to determine if a string could be a valid JSON value; parseMaybeJson calls JSON.parse only when that check passes. defaultParseSearch is updated to use parseMaybeJson instead of JSON.parse directly. New tests and a changeset accompany the change.

Changes

defaultParseSearch JSON parse guard

Layer / File(s)

Summary

couldBeJson / parseMaybeJson helpers and defaultParseSearch wiring packages/router-core/src/searchParams.ts, packages/router-core/tests/searchParams.test.ts, .changeset/perf-default-search-parse-guard.md

couldBeJson scans past leading whitespace and checks the first character against valid JSON-start characters. parseMaybeJson wraps JSON.parse behind that guard, returning the raw string when the check fails. defaultParseSearch is switched from parseSearchWith(JSON.parse) to parseSearchWith(parseMaybeJson). Tests cover plain strings, leading-whitespace JSON, invalid JSON-looking inputs, and non-literal t/f/n-prefixed words. The changeset documents the performance motivation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related issues

• defaultParseSearch corrupts string search params that look like JSON numbers (e.g. "662E41", large integers) — lossy and unrecoverable on inbound URLs #7650 — Both this PR and that issue modify defaultParseSearch in searchParams.ts to add a guard before JSON.parse; the issue specifically targets precision-loss coercion of hex strings like "662E41" to numbers, which is a distinct case the first-character heuristic here does not address (hex strings start with a digit 6, which couldBeJson would pass).

Suggested labels

package: router-core

Suggested reviewers

• chorobin

Poem

🐇 Hop hop, no parse for thee,
A string that starts with h runs free!
No more throw/catch on every quest,
couldBeJson guards the nest.
Less overhead, more speedy ways—
The router hops through query haze! 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'perf(router-core): guard default search parser against throws' directly and specifically describes the main change—adding a guard to prevent expensive JSON.parse throws in the default search parser, which is the core optimization in this PR.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[nx-cloud]

View your CI Pipeline Execution ↗ for commit b4a3303

Command	Status	Duration	Result
nx affected --targets=test:eslint,test:unit,tes...	❌ Failed	22m 33s	View ↗
nx run-many --target=build --exclude=examples/*...	✅ Succeeded	2m 17s	View ↗

---

☁️ Nx Cloud last updated this comment at 2026-06-22 13:53:24 UTC

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commit: b4a3303

[codspeed-hq]

Merging this PR will degrade performance by 11.83%

❌ 3 regressed benchmarks
✅ 141 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	mem serialization-payload (vue)	6.8 MB	8.7 MB	-22.2%
❌	Memory	mem aborted-requests (vue)	959.1 KB	1,048.9 KB	-8.56%
❌	Memory	mem request-churn (vue)	1.3 MB	1.3 MB	-3.66%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing anonrig:perf/default-search-parse-guard (b4a3303) with main (f23ed0f)¹}

Footnotes

1. No successful run was found on main (279a849) during the generation of this report, so f23ed0f was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[nx-cloud]

Nx Cloud has identified a possible root cause for your failed CI:

We classified this failure as an environment state issue rather than a code change. The error — a missing resolveRuntimeSuffix export in e2e/e2e-utils/dist/esm/index.js — points to stale or inconsistently built dist artifacts in the e2e test infrastructure, which has no relation to the @tanstack/router-core search param optimization introduced by this PR. Rebuilding the e2e-utils package should restore consistent artifacts and resolve the failure.

No code changes were suggested for this issue.

You can trigger a rerun by pushing an empty commit:

git commit --allow-empty -m "chore: trigger rerun"
git push

View detailed reasoning on Nx Cloud ↗

_{🎓 Learn more about Self-Healing CI on nx.dev}

[anonrig]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

[Sheraff]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

I already had a pretty similar PR a while ago https://github.com/TanStack/router/pull/5071/changes

not sure why we never merged it.

[anonrig]

What

Stop the default search parser from throwing a SyntaxError for every plain-string param. In packages/router-core/src/searchParams.ts, defaultParseSearch ran JSON.parse on every leftover string value:

-export const defaultParseSearch = parseSearchWith(JSON.parse)+export const defaultParseSearch = parseSearchWith(parseMaybeJson)

parseMaybeJson first checks, from the first non-whitespace character, whether the value could be JSON and only then calls JSON.parse. The check is a superset of JSON's value-start grammar ({ [ " -0-9t f n, skipping leading whitespace), so any string JSON.parse would accept still gets parsed — we only skip the doomed parse of plain strings.

Why

qss.decode already coerces numbers/booleans, so JSON.parse only ever runs on the remaining string values — which on real apps are mostly plain text (?q=hello&f=live&src=typed_query). Each one throws a SyntaxError that parseSearchWith catches to keep the raw string, and constructing + throwing that error (with stack capture) is the dominant cost.

Search params are parsed on every SSR request and every client navigation. In-situ before/after on the real defaultParseSearch (Vitest bench):

Query shape	old (JSON.parse)	new (guarded)	Speedup
mixed X-like (?q=…&f=live&src=…&pf=1)	317K ops/s	996K ops/s	3.1×
all plain strings (?q=from:elon since:2024&f=live&…)	107K ops/s	176K ops/s	1.7×

Correctness

Behavior is identical. The guard never skips a value JSON.parse would accept, and for skipped values it returns the raw string — exactly what parseSearchWith does today when JSON.parse throws.

Verified by:

• The full existing searchParams suite (isomorphism round-trips + "alien deserialization" of human-typed params).
• A 5000+ case fuzz confirming couldBeJson is a correct superset of JSON.parse's accept set.
• Four added tests: plain-string params stay strings, leading-whitespace JSON values still parse (guard skips whitespace), JSON-looking-but-invalid values fall back to the raw string, and t/f/n-prefixed non-literals (tweet, false_alarm, null_island) stay strings.

nx run @tanstack/router-core:test:unit -> 1182 passed (+ 3 expected-fail)
nx run @tanstack/router-core:test:types -> no errors

Notes

• Only the default parse path changes. defaultStringifySearch uses the same JSON.parse-as-throw-probe pattern when building URLs (also hot via <Link>), but its logic relies on throw-vs-no-throw as the "is this JSON?" signal, so making it allocation-free cleanly is a slightly larger change — happy to do it as a follow-up.
• Includes a changeset (@tanstack/router-core patch).
• Pre-existing unused-imports/no-unused-vars warnings on the existing catch (_err) blocks are untouched by this change.

Summary by CodeRabbit

• Performance
  • Optimized query parameter parsing to reduce processing overhead, improving performance for server-side rendering and client-side navigation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 81d1c0ab-ecfc-4d71-a1b9-8028d3b188c0

📥 Commits

Reviewing files that changed from the base of the PR and between 279a849 and b4a3303.

📒 Files selected for processing (3)

• .changeset/perf-default-search-parse-guard.md
• packages/router-core/src/searchParams.ts
• packages/router-core/tests/searchParams.test.ts

---

📝 Walkthrough

Walkthrough

Adds two internal helpers (couldBeJson and parseMaybeJson) to searchParams.ts. couldBeJson checks the first non-whitespace character to determine if a string could be a valid JSON value; parseMaybeJson calls JSON.parse only when that check passes. defaultParseSearch is updated to use parseMaybeJson instead of JSON.parse directly. New tests and a changeset accompany the change.

Changes

defaultParseSearch JSON parse guard

Layer / File(s)

Summary

couldBeJson / parseMaybeJson helpers and defaultParseSearch wiring packages/router-core/src/searchParams.ts, packages/router-core/tests/searchParams.test.ts, .changeset/perf-default-search-parse-guard.md

couldBeJson scans past leading whitespace and checks the first character against valid JSON-start characters. parseMaybeJson wraps JSON.parse behind that guard, returning the raw string when the check fails. defaultParseSearch is switched from parseSearchWith(JSON.parse) to parseSearchWith(parseMaybeJson). Tests cover plain strings, leading-whitespace JSON, invalid JSON-looking inputs, and non-literal t/f/n-prefixed words. The changeset documents the performance motivation.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related issues

• defaultParseSearch corrupts string search params that look like JSON numbers (e.g. "662E41", large integers) — lossy and unrecoverable on inbound URLs #7650 — Both this PR and that issue modify defaultParseSearch in searchParams.ts to add a guard before JSON.parse; the issue specifically targets precision-loss coercion of hex strings like "662E41" to numbers, which is a distinct case the first-character heuristic here does not address (hex strings start with a digit 6, which couldBeJson would pass).

Suggested labels

package: router-core

Suggested reviewers

• chorobin

Poem

🐇 Hop hop, no parse for thee,
A string that starts with h runs free!
No more throw/catch on every quest,
couldBeJson guards the nest.
Less overhead, more speedy ways—
The router hops through query haze! 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'perf(router-core): guard default search parser against throws' directly and specifically describes the main change—adding a guard to prevent expensive JSON.parse throws in the default search parser, which is the core optimization in this PR.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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🧪 Generate unit tests (beta)

• Create PR with unit tests

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[nx-cloud]

View your CI Pipeline Execution ↗ for commit b4a3303

Command	Status	Duration	Result
nx affected --targets=test:eslint,test:unit,tes...	❌ Failed	22m 33s	View ↗
nx run-many --target=build --exclude=examples/*...	✅ Succeeded	2m 17s	View ↗

---

☁️ Nx Cloud last updated this comment at 2026-06-22 13:53:24 UTC

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commit: b4a3303

[codspeed-hq]

Merging this PR will degrade performance by 11.83%

❌ 3 regressed benchmarks
✅ 141 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	mem serialization-payload (vue)	6.8 MB	8.7 MB	-22.2%
❌	Memory	mem aborted-requests (vue)	959.1 KB	1,048.9 KB	-8.56%
❌	Memory	mem request-churn (vue)	1.3 MB	1.3 MB	-3.66%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing anonrig:perf/default-search-parse-guard (b4a3303) with main (f23ed0f)¹}

Footnotes

1. No successful run was found on main (279a849) during the generation of this report, so f23ed0f was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[nx-cloud]

Nx Cloud has identified a possible root cause for your failed CI:

We classified this failure as an environment state issue rather than a code change. The error — a missing resolveRuntimeSuffix export in e2e/e2e-utils/dist/esm/index.js — points to stale or inconsistently built dist artifacts in the e2e test infrastructure, which has no relation to the @tanstack/router-core search param optimization introduced by this PR. Rebuilding the e2e-utils package should restore consistent artifacts and resolve the failure.

No code changes were suggested for this issue.

You can trigger a rerun by pushing an empty commit:

git commit --allow-empty -m "chore: trigger rerun"
git push

View detailed reasoning on Nx Cloud ↗

_{🎓 Learn more about Self-Healing CI on nx.dev}

[anonrig]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

[Sheraff]

I'm closing this because Tanstack router repository has a limit of maximum number of pull-request open per a user and it is 6!!!!!

I already had a pretty similar PR a while ago https://github.com/TanStack/router/pull/5071/changes

not sure why we never merged it.