fix(server): handle undefined arguments for tools with all optional params - #1404

Merged
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom
su-ram:fix/400-optional-params-validation
Jan 23, 2026
Merged

fix(server): handle undefined arguments for tools with all optional params#1404
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom
su-ram:fix/400-optional-params-validation

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@su-ramsu-ram commented Jan 19, 2026

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Fixes#400

Motivation and Context

When a tool has all optional parameters, some LLM models call the tool without providing an
arguments field. This causes Zod validation to fail with:

MCP error -32602: Invalid arguments for tool [name]: Invalid input: expected object, received
undefined

Even though the schema allows all fields to be optional, Zod's z.object() expects the input
itself to be an object, not undefined or null.

How Has This Been Tested?

  • Added unit test: should accept undefined arguments when all tool params are optional
  • Verified Zod behavior with direct testing:
    • undefined → fails with "expected object, received undefined"
    • null → fails with "expected object, received null"
    • {} → passes validation
  • All existing tests pass (1,392 tests)

Breaking Changes

None. This is a backward-compatible fix that only affects edge cases where arguments is
omitted.

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Documentation update

Checklist

  • I have read the MCP Documentation
  • My code follows the repository's style guidelines
  • New and existing tests pass locally
  • I have added appropriate error handling
  • I have added or updated documentation as needed

Additional context

The fix is a single line change in packages/server/src/server/mcp.ts:

// Before constparseResult=awaitsafeParseAsync(schemaToParse,args);// After constparseResult=awaitsafeParseAsync(schemaToParse,args??{});Using??handlesbothundefinedandnullcases.

@su-ram
su-ram requested a review from a team as a code ownerJanuary 19, 2026 12:31
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Latest commit: 33019b1

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npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1404

@modelcontextprotocol/server

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1404

@modelcontextprotocol/express

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1404

@modelcontextprotocol/hono

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1404

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commit: 33019b1

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felixweinberger approved these changes Jan 23, 2026
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Thanks for the fix! This aligns with how the Python SDK handles the same case (arguments or {}).

I made a couple small changes:

  • Updated the test to use registerTool instead of the deprecated tool method
  • Moved the test to test/issues/test400.optional-tool-params.test.ts to match our pattern for regression tests

@felixweinberger
felixweinberger merged commit b2326af into modelcontextprotocol:mainJan 23, 2026
10 checks passed
@dgon-jddgon-jd mentioned this pull request Apr 9, 2026
Open
@carlesandrescarlesandres mentioned this pull request Apr 14, 2026
Closed
Christian-Sidak added a commit to Christian-Sidak/typescript-sdk that referenced this pull request Apr 17, 2026
@Christian-Sidak
fix: prompts/get rejects omitted arguments when all argsSchema fields…
b1db976
… are optional
Mirror the tools fix from modelcontextprotocol#1404 to the prompts handler: default
undefined arguments to {} before schema validation so that a prompt
with all-optional argsSchema fields accepts a request that omits
arguments entirely.
Closesmodelcontextprotocol#1869
@Christian-SidakChristian-Sidak mentioned this pull request Apr 17, 2026
Closed
@lux999lux999 mentioned this pull request Apr 19, 2026
Open
9 tasks
@Jim1874Jim1874 mentioned this pull request Apr 20, 2026
Open
@coderabbitaicoderabbitaiBot mentioned this pull request Jul 15, 2026
Merged
2 tasks
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InvalidParams error when all fields in the tool schema are optional

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, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

Skip to content
fix(server): handle undefined arguments for tools with all optional params - #1404
Merged
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Jan 23, 2026
Merged
fix(server): handle undefined arguments for tools with all optional params#1404
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Conversation
@su-ram
@su-ramsu-ram
commented
Jan 19, 2026

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Contributor
Fixes#400
Motivation and Context
When a tool has all optional parameters, some LLM models call the tool without providing an
arguments field. This causes Zod validation to fail with:
MCP error -32602: Invalid arguments for tool [name]: Invalid input: expected object, received

undefined
Even though the schema allows all fields to be optional, Zod's z.object() expects the input

itself to be an object, not undefined or null.
How Has This Been Tested?
  • Added unit test: should accept undefined arguments when all tool params are optional
  • Verified Zod behavior with direct testing:

    • undefined → fails with "expected object, received undefined"
    • null → fails with "expected object, received null"
    • {} → passes validation
  • All existing tests pass (1,392 tests)
Breaking Changes
None. This is a backward-compatible fix that only affects edge cases where arguments is

omitted.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
The fix is a single line change in packages/server/src/server/mcp.ts:
// Before constparseResult=awaitsafeParseAsync(schemaToParse,args);// After constparseResult=awaitsafeParseAsync(schemaToParse,args??{});Using??handlesbothundefinedandnullcases.
@su-ram
su-ram
requested a review
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as a code ownerJanuary 19, 2026 12:31
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Latest commit: 33019b1
Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
Click here to learn what changesets are, and how to add one.
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@modelcontextprotocol/client
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1404

@modelcontextprotocol/server
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1404

@modelcontextprotocol/express
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1404

@modelcontextprotocol/hono
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1404

@modelcontextprotocol/node
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@1404

commit: 33019b1
felixweinberger
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Thanks for the fix! This aligns with how the Python SDK handles the same case (arguments or {}).
I made a couple small changes:
  • Updated the test to use registerTool instead of the deprecated tool method
  • Moved the test to test/issues/test400.optional-tool-params.test.ts to match our pattern for regression tests
@felixweinberger
felixweinberger
merged commit b2326af
into
modelcontextprotocol:mainJan 23, 2026

10 checks passed

@dgon-jddgon-jd
mentioned this pull request
Apr 9, 2026

Open

@carlesandrescarlesandres
mentioned this pull request
Apr 14, 2026

Closed

Christian-Sidak added a commit
to Christian-Sidak/typescript-sdk
that referenced
this pull request
Apr 17, 2026
@Christian-Sidak
fix: prompts/get rejects omitted arguments when all argsSchema fields…
b1db976
… are optional
Mirror the tools fix from modelcontextprotocol#1404 to the prompts handler: default
undefined arguments to {} before schema validation so that a prompt
with all-optional argsSchema fields accepts a request that omits
arguments entirely.
Closesmodelcontextprotocol#1869
@Christian-SidakChristian-Sidak
mentioned this pull request
Apr 17, 2026
 Closed

@lux999lux999
mentioned this pull request
Apr 19, 2026
 Open

9 tasks
@Jim1874Jim1874
mentioned this pull request
Apr 20, 2026
 Open

@coderabbitaicoderabbitaiBot
mentioned this pull request
Jul 15, 2026
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2 tasks
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InvalidParams error when all fields in the tool schema are optional


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@su-ram@felixweinberger

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix(server): handle undefined arguments for tools with all optional params - #1404
Merged
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Jan 23, 2026
Merged
fix(server): handle undefined arguments for tools with all optional params#1404
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Conversation
@su-ram
@su-ramsu-ram
commented
Jan 19, 2026

Copy link


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Contributor
Fixes#400
Motivation and Context
When a tool has all optional parameters, some LLM models call the tool without providing an
arguments field. This causes Zod validation to fail with:
MCP error -32602: Invalid arguments for tool [name]: Invalid input: expected object, received

undefined
Even though the schema allows all fields to be optional, Zod's z.object() expects the input

itself to be an object, not undefined or null.
How Has This Been Tested?
  • Added unit test: should accept undefined arguments when all tool params are optional
  • Verified Zod behavior with direct testing:

    • undefined → fails with "expected object, received undefined"
    • null → fails with "expected object, received null"
    • {} → passes validation
  • All existing tests pass (1,392 tests)
Breaking Changes
None. This is a backward-compatible fix that only affects edge cases where arguments is

omitted.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
The fix is a single line change in packages/server/src/server/mcp.ts:
// Before constparseResult=awaitsafeParseAsync(schemaToParse,args);// After constparseResult=awaitsafeParseAsync(schemaToParse,args??{});Using??handlesbothundefinedandnullcases.
@su-ram
su-ram
requested a review
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as a code ownerJanuary 19, 2026 12:31
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Jan 19, 2026•

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⚠️ No Changeset found
Latest commit: 33019b1
Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
Click here to learn what changesets are, and how to add one.
Click here if you're a maintainer who wants to add a changeset to this PR
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@modelcontextprotocol/client
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1404

@modelcontextprotocol/server
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1404

@modelcontextprotocol/express
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1404

@modelcontextprotocol/hono
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1404

@modelcontextprotocol/node
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@1404

commit: 33019b1
felixweinberger
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Thanks for the fix! This aligns with how the Python SDK handles the same case (arguments or {}).
I made a couple small changes:
  • Updated the test to use registerTool instead of the deprecated tool method
  • Moved the test to test/issues/test400.optional-tool-params.test.ts to match our pattern for regression tests
@felixweinberger
felixweinberger
merged commit b2326af
into
modelcontextprotocol:mainJan 23, 2026

10 checks passed

@dgon-jddgon-jd
mentioned this pull request
Apr 9, 2026

Open

@carlesandrescarlesandres
mentioned this pull request
Apr 14, 2026

Closed

Christian-Sidak added a commit
to Christian-Sidak/typescript-sdk
that referenced
this pull request
Apr 17, 2026
@Christian-Sidak
fix: prompts/get rejects omitted arguments when all argsSchema fields…
b1db976
… are optional
Mirror the tools fix from modelcontextprotocol#1404 to the prompts handler: default
undefined arguments to {} before schema validation so that a prompt
with all-optional argsSchema fields accepts a request that omits
arguments entirely.
Closesmodelcontextprotocol#1869
@Christian-SidakChristian-Sidak
mentioned this pull request
Apr 17, 2026
 Closed

@lux999lux999
mentioned this pull request
Apr 19, 2026
 Open

9 tasks
@Jim1874Jim1874
mentioned this pull request
Apr 20, 2026
 Open

@coderabbitaicoderabbitaiBot
mentioned this pull request
Jul 15, 2026
 Merged

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InvalidParams error when all fields in the tool schema are optional


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@su-ram@felixweinberger

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix(server): handle undefined arguments for tools with all optional params - #1404
Merged
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Jan 23, 2026
Merged
fix(server): handle undefined arguments for tools with all optional params#1404
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Conversation
@su-ram
@su-ramsu-ram
commented
Jan 19, 2026

Copy link


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Contributor
Fixes#400
Motivation and Context
When a tool has all optional parameters, some LLM models call the tool without providing an
arguments field. This causes Zod validation to fail with:
MCP error -32602: Invalid arguments for tool [name]: Invalid input: expected object, received

undefined
Even though the schema allows all fields to be optional, Zod's z.object() expects the input

itself to be an object, not undefined or null.
How Has This Been Tested?
  • Added unit test: should accept undefined arguments when all tool params are optional
  • Verified Zod behavior with direct testing:

    • undefined → fails with "expected object, received undefined"
    • null → fails with "expected object, received null"
    • {} → passes validation
  • All existing tests pass (1,392 tests)
Breaking Changes
None. This is a backward-compatible fix that only affects edge cases where arguments is

omitted.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
The fix is a single line change in packages/server/src/server/mcp.ts:
// Before constparseResult=awaitsafeParseAsync(schemaToParse,args);// After constparseResult=awaitsafeParseAsync(schemaToParse,args??{});Using??handlesbothundefinedandnullcases.
@su-ram
su-ram
requested a review
from a team
as a code ownerJanuary 19, 2026 12:31
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⚠️ No Changeset found
Latest commit: 33019b1
Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
Click here to learn what changesets are, and how to add one.
Click here if you're a maintainer who wants to add a changeset to this PR
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@modelcontextprotocol/client
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1404

@modelcontextprotocol/server
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1404

@modelcontextprotocol/express
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1404

@modelcontextprotocol/hono
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1404

@modelcontextprotocol/node
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@1404

commit: 33019b1
felixweinberger
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approved these changes
Jan 23, 2026
View reviewed changes
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Thanks for the fix! This aligns with how the Python SDK handles the same case (arguments or {}).
I made a couple small changes:
  • Updated the test to use registerTool instead of the deprecated tool method
  • Moved the test to test/issues/test400.optional-tool-params.test.ts to match our pattern for regression tests
@felixweinberger
felixweinberger
merged commit b2326af
into
modelcontextprotocol:mainJan 23, 2026

10 checks passed

@dgon-jddgon-jd
mentioned this pull request
Apr 9, 2026

Open

@carlesandrescarlesandres
mentioned this pull request
Apr 14, 2026

Closed

Christian-Sidak added a commit
to Christian-Sidak/typescript-sdk
that referenced
this pull request
Apr 17, 2026
@Christian-Sidak
fix: prompts/get rejects omitted arguments when all argsSchema fields…
b1db976
… are optional
Mirror the tools fix from modelcontextprotocol#1404 to the prompts handler: default
undefined arguments to {} before schema validation so that a prompt
with all-optional argsSchema fields accepts a request that omits
arguments entirely.
Closesmodelcontextprotocol#1869
@Christian-SidakChristian-Sidak
mentioned this pull request
Apr 17, 2026
 Closed

@lux999lux999
mentioned this pull request
Apr 19, 2026
 Open

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@Jim1874Jim1874
mentioned this pull request
Apr 20, 2026
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Jul 15, 2026
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InvalidParams error when all fields in the tool schema are optional


2 participants

@su-ram@felixweinberger

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

Skip to content
fix(server): handle undefined arguments for tools with all optional params - #1404
Merged
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Jan 23, 2026
Merged
fix(server): handle undefined arguments for tools with all optional params#1404
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Conversation
@su-ram
@su-ramsu-ram
commented
Jan 19, 2026

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Contributor
Fixes#400
Motivation and Context
When a tool has all optional parameters, some LLM models call the tool without providing an
arguments field. This causes Zod validation to fail with:
MCP error -32602: Invalid arguments for tool [name]: Invalid input: expected object, received

undefined
Even though the schema allows all fields to be optional, Zod's z.object() expects the input

itself to be an object, not undefined or null.
How Has This Been Tested?
  • Added unit test: should accept undefined arguments when all tool params are optional
  • Verified Zod behavior with direct testing:

    • undefined → fails with "expected object, received undefined"
    • null → fails with "expected object, received null"
    • {} → passes validation
  • All existing tests pass (1,392 tests)
Breaking Changes
None. This is a backward-compatible fix that only affects edge cases where arguments is

omitted.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
The fix is a single line change in packages/server/src/server/mcp.ts:
// Before constparseResult=awaitsafeParseAsync(schemaToParse,args);// After constparseResult=awaitsafeParseAsync(schemaToParse,args??{});Using??handlesbothundefinedandnullcases.
@su-ram
su-ram
requested a review
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as a code ownerJanuary 19, 2026 12:31
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Jan 19, 2026•

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⚠️ No Changeset found
Latest commit: 33019b1
Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
Click here to learn what changesets are, and how to add one.
Click here if you're a maintainer who wants to add a changeset to this PR
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@modelcontextprotocol/client
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1404

@modelcontextprotocol/server
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1404

@modelcontextprotocol/express
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1404

@modelcontextprotocol/hono
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1404

@modelcontextprotocol/node
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@1404

commit: 33019b1
felixweinberger
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Jan 23, 2026
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Thanks for the fix! This aligns with how the Python SDK handles the same case (arguments or {}).
I made a couple small changes:
  • Updated the test to use registerTool instead of the deprecated tool method
  • Moved the test to test/issues/test400.optional-tool-params.test.ts to match our pattern for regression tests
@felixweinberger
felixweinberger
merged commit b2326af
into
modelcontextprotocol:mainJan 23, 2026

10 checks passed

@dgon-jddgon-jd
mentioned this pull request
Apr 9, 2026

Open

@carlesandrescarlesandres
mentioned this pull request
Apr 14, 2026

Closed

Christian-Sidak added a commit
to Christian-Sidak/typescript-sdk
that referenced
this pull request
Apr 17, 2026
@Christian-Sidak
fix: prompts/get rejects omitted arguments when all argsSchema fields…
b1db976
… are optional
Mirror the tools fix from modelcontextprotocol#1404 to the prompts handler: default
undefined arguments to {} before schema validation so that a prompt
with all-optional argsSchema fields accepts a request that omits
arguments entirely.
Closesmodelcontextprotocol#1869
@Christian-SidakChristian-Sidak
mentioned this pull request
Apr 17, 2026
 Closed

@lux999lux999
mentioned this pull request
Apr 19, 2026
 Open

9 tasks
@Jim1874Jim1874
mentioned this pull request
Apr 20, 2026
 Open

@coderabbitaicoderabbitaiBot
mentioned this pull request
Jul 15, 2026
 Merged

2 tasks
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InvalidParams error when all fields in the tool schema are optional


2 participants

@su-ram@felixweinberger

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix(server): handle undefined arguments for tools with all optional params - #1404
Merged
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Jan 23, 2026
Merged
fix(server): handle undefined arguments for tools with all optional params#1404
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Conversation
@su-ram
@su-ramsu-ram
commented
Jan 19, 2026

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Contributor
Fixes#400
Motivation and Context
When a tool has all optional parameters, some LLM models call the tool without providing an
arguments field. This causes Zod validation to fail with:
MCP error -32602: Invalid arguments for tool [name]: Invalid input: expected object, received

undefined
Even though the schema allows all fields to be optional, Zod's z.object() expects the input

itself to be an object, not undefined or null.
How Has This Been Tested?
  • Added unit test: should accept undefined arguments when all tool params are optional
  • Verified Zod behavior with direct testing:

    • undefined → fails with "expected object, received undefined"
    • null → fails with "expected object, received null"
    • {} → passes validation
  • All existing tests pass (1,392 tests)
Breaking Changes
None. This is a backward-compatible fix that only affects edge cases where arguments is

omitted.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
The fix is a single line change in packages/server/src/server/mcp.ts:
// Before constparseResult=awaitsafeParseAsync(schemaToParse,args);// After constparseResult=awaitsafeParseAsync(schemaToParse,args??{});Using??handlesbothundefinedandnullcases.
@su-ram
su-ram
requested a review
from a team
as a code ownerJanuary 19, 2026 12:31
@changeset-bot
changeset-botBot
commented
Jan 19, 2026•

edited

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⚠️ No Changeset found
Latest commit: 33019b1
Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
Click here to learn what changesets are, and how to add one.
Click here if you're a maintainer who wants to add a changeset to this PR
@pkg-pr-new
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Jan 19, 2026•

edited

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@modelcontextprotocol/client
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1404

@modelcontextprotocol/server
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1404

@modelcontextprotocol/express
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1404

@modelcontextprotocol/hono
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1404

@modelcontextprotocol/node
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@1404

commit: 33019b1
felixweinberger
felixweinberger
approved these changes
Jan 23, 2026
View reviewed changes
@felixweinbergerfelixweinberger
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Thanks for the fix! This aligns with how the Python SDK handles the same case (arguments or {}).
I made a couple small changes:
  • Updated the test to use registerTool instead of the deprecated tool method
  • Moved the test to test/issues/test400.optional-tool-params.test.ts to match our pattern for regression tests
@felixweinberger
felixweinberger
merged commit b2326af
into
modelcontextprotocol:mainJan 23, 2026

10 checks passed

@dgon-jddgon-jd
mentioned this pull request
Apr 9, 2026

Open

@carlesandrescarlesandres
mentioned this pull request
Apr 14, 2026

Closed

Christian-Sidak added a commit
to Christian-Sidak/typescript-sdk
that referenced
this pull request
Apr 17, 2026
@Christian-Sidak
fix: prompts/get rejects omitted arguments when all argsSchema fields…
b1db976
… are optional
Mirror the tools fix from modelcontextprotocol#1404 to the prompts handler: default
undefined arguments to {} before schema validation so that a prompt
with all-optional argsSchema fields accepts a request that omits
arguments entirely.
Closesmodelcontextprotocol#1869
@Christian-SidakChristian-Sidak
mentioned this pull request
Apr 17, 2026
 Closed

@lux999lux999
mentioned this pull request
Apr 19, 2026
 Open

9 tasks
@Jim1874Jim1874
mentioned this pull request
Apr 20, 2026
 Open

@coderabbitaicoderabbitaiBot
mentioned this pull request
Jul 15, 2026
 Merged

2 tasks
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Successfully merging this pull request may close these issues.

InvalidParams error when all fields in the tool schema are optional


2 participants

@su-ram@felixweinberger

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix(server): handle undefined arguments for tools with all optional params - #1404
Merged
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Jan 23, 2026
Merged
fix(server): handle undefined arguments for tools with all optional params#1404
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Conversation
@su-ram
@su-ramsu-ram
commented
Jan 19, 2026

Copy link


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Contributor
Fixes#400
Motivation and Context
When a tool has all optional parameters, some LLM models call the tool without providing an
arguments field. This causes Zod validation to fail with:
MCP error -32602: Invalid arguments for tool [name]: Invalid input: expected object, received

undefined
Even though the schema allows all fields to be optional, Zod's z.object() expects the input

itself to be an object, not undefined or null.
How Has This Been Tested?
  • Added unit test: should accept undefined arguments when all tool params are optional
  • Verified Zod behavior with direct testing:

    • undefined → fails with "expected object, received undefined"
    • null → fails with "expected object, received null"
    • {} → passes validation
  • All existing tests pass (1,392 tests)
Breaking Changes
None. This is a backward-compatible fix that only affects edge cases where arguments is

omitted.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
The fix is a single line change in packages/server/src/server/mcp.ts:
// Before constparseResult=awaitsafeParseAsync(schemaToParse,args);// After constparseResult=awaitsafeParseAsync(schemaToParse,args??{});Using??handlesbothundefinedandnullcases.
@su-ram
su-ram
requested a review
from a team
as a code ownerJanuary 19, 2026 12:31
@changeset-bot
changeset-botBot
commented
Jan 19, 2026•

edited

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⚠️ No Changeset found
Latest commit: 33019b1
Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.
This PR includes no changesets
When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types
Click here to learn what changesets are, and how to add one.
Click here if you're a maintainer who wants to add a changeset to this PR
@pkg-pr-new
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Jan 19, 2026•

edited

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@modelcontextprotocol/client
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1404

@modelcontextprotocol/server
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1404

@modelcontextprotocol/express
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@1404

@modelcontextprotocol/hono
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@1404

@modelcontextprotocol/node
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@1404

commit: 33019b1
felixweinberger
felixweinberger
approved these changes
Jan 23, 2026
View reviewed changes
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Thanks for the fix! This aligns with how the Python SDK handles the same case (arguments or {}).
I made a couple small changes:
  • Updated the test to use registerTool instead of the deprecated tool method
  • Moved the test to test/issues/test400.optional-tool-params.test.ts to match our pattern for regression tests
@felixweinberger
felixweinberger
merged commit b2326af
into
modelcontextprotocol:mainJan 23, 2026

10 checks passed

@dgon-jddgon-jd
mentioned this pull request
Apr 9, 2026

Open

@carlesandrescarlesandres
mentioned this pull request
Apr 14, 2026

Closed

Christian-Sidak added a commit
to Christian-Sidak/typescript-sdk
that referenced
this pull request
Apr 17, 2026
@Christian-Sidak
fix: prompts/get rejects omitted arguments when all argsSchema fields…
b1db976
… are optional
Mirror the tools fix from modelcontextprotocol#1404 to the prompts handler: default
undefined arguments to {} before schema validation so that a prompt
with all-optional argsSchema fields accepts a request that omits
arguments entirely.
Closesmodelcontextprotocol#1869
@Christian-SidakChristian-Sidak
mentioned this pull request
Apr 17, 2026
 Closed

@lux999lux999
mentioned this pull request
Apr 19, 2026
 Open

9 tasks
@Jim1874Jim1874
mentioned this pull request
Apr 20, 2026
 Open

@coderabbitaicoderabbitaiBot
mentioned this pull request
Jul 15, 2026
 Merged

2 tasks
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Successfully merging this pull request may close these issues.

InvalidParams error when all fields in the tool schema are optional


2 participants

@su-ram@felixweinberger

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

Skip to content
fix(server): handle undefined arguments for tools with all optional params - #1404
Merged
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Jan 23, 2026
Merged
fix(server): handle undefined arguments for tools with all optional params#1404
felixweinberger merged 5 commits into
modelcontextprotocol:mainfrom 
su-ram:fix/400-optional-params-validation
Conversation
@su-ram
@su-ramsu-ram
commented
Jan 19, 2026

Copy link


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Contributor
Fixes#400
Motivation and Context
When a tool has all optional parameters, some LLM models call the tool without providing an
arguments field. This causes Zod validation to fail with:
MCP error -32602: Invalid arguments for tool [name]: Invalid input: expected object, received

undefined
Even though the schema allows all fields to be optional, Zod's z.object() expects the input

itself to be an object, not undefined or null.
How Has This Been Tested?
  • Added unit test: should accept undefined arguments when all tool params are optional
  • Verified Zod behavior with direct testing:

    • undefined → fails with "expected object, received undefined"
    • null → fails with "expected object, received null"
    • {} → passes validation
  • All existing tests pass (1,392 tests)
Breaking Changes
None. This is a backward-compatible fix that only affects edge cases where arguments is

omitted.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
The fix is a single line change in packages/server/src/server/mcp.ts:
// Before constparseResult=awaitsafeParseAsync(schemaToParse,args);// After constparseResult=awaitsafeParseAsync(schemaToParse,args??{});Using??handlesbothundefinedandnullcases.
@su-ram
su-ram
requested a review
from a team
as a code ownerJanuary 19, 2026 12:31
@changeset-bot
changeset-botBot
commented
Jan 19, 2026•

edited

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@modelcontextprotocol/client
npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@1404

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npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@1404

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commit: 33019b1
felixweinberger
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Thanks for the fix! This aligns with how the Python SDK handles the same case (arguments or {}).
I made a couple small changes:
  • Updated the test to use registerTool instead of the deprecated tool method
  • Moved the test to test/issues/test400.optional-tool-params.test.ts to match our pattern for regression tests
@felixweinberger
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modelcontextprotocol:mainJan 23, 2026

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@dgon-jddgon-jd
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Christian-Sidak added a commit
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Apr 17, 2026
@Christian-Sidak
fix: prompts/get rejects omitted arguments when all argsSchema fields…
b1db976
… are optional
Mirror the tools fix from modelcontextprotocol#1404 to the prompts handler: default
undefined arguments to {} before schema validation so that a prompt
with all-optional argsSchema fields accepts a request that omits
arguments entirely.
Closesmodelcontextprotocol#1869
@Christian-SidakChristian-Sidak
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Apr 17, 2026
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InvalidParams error when all fields in the tool schema are optional


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