fix: tools-call-simple-text now fails when tool returns isError: true - #165

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modelcontextprotocol:mainfrom
lux999:fix/tools-call-simple-text-iserror-check
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fix: tools-call-simple-text now fails when tool returns isError: true#165
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom
lux999:fix/tools-call-simple-text-iserror-check

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@lux999lux999 commented Feb 24, 2026

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Added an isError check to ToolsCallSimpleTextScenario, so the test tools-call-simple-text correctly fails when the tool returns an error result instead of a successful text response.

Motivation and Context

The test tools-call-simple-text was passing for servers that don't implement test_simple_text at all.
When an unknown tool is called, MCP frameworks return { isError: true, content: [{ type: "text", text: "Tool not found: ..." }] }. The existing assertions only checked for a non-empty text content item, which the "Tool not found" error message satisfies. The missing assertion was that result.isError must not be true.

How Has This Been Tested?

Verified against the existing everything-server reference implementation, which correctly implements test_simple_text and continues to pass. Confirmed that servers without test_simple_text now correctly fail the test.

Breaking Changes

Servers that were previously passing tools-call-simple-text without implementing test_simple_text will now correctly fail.

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

pcarleton
pcarleton previously approved these changes Mar 25, 2026
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LGTM, thanks!

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pcarleton enabled auto-merge (squash) March 25, 2026 12:10
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commit: cd062a6

auto-merge was automatically disabled April 19, 2026 20:13

Head branch was pushed to by a user without write access

alu
fix: pass empty arguments object in tools-call-simple-text scenario
3af5ac4
The reference everything-server's zod schema rejects `undefined` arguments
and requires at least `{}`, so omitting `arguments` caused the server to
return `isError: true` with a validation error. This went unnoticed under
the previous lenient check but is correctly flagged by the new `isError`
assertion. Matches the convention used by every other tool-call scenario
in this file.
@lux999
lux999force-pushed the fix/tools-call-simple-text-iserror-check branch from 04febed to 3af5ac4CompareApril 19, 2026 20:41
@lux999

lux999 commented Apr 19, 2026

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Hi @pcarleton, thanks for the approval!

Quick heads-up on the new commit: after merging main, CI caught one test failure. This scenario originally omitted arguments since they're not required for test_simple_text, but the upstream SDK server rejects undefined arguments against any inputSchema and returns isError: true - which the new check correctly flags. There's an upstream fix in typescript-sdk#1404 but it wasn't backported to 1.x - see typescript-sdk#1869.

I squashed a small workaround into the fix commit: pass arguments: {} explicitly, with an inline comment linking to the SDK issue. Matches the convention in the sibling tool-call scenarios. Happy to revisit if you'd prefer a different approach.

Thanks again!

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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: tools-call-simple-text now fails when tool returns isError: true - #165
Open
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Open
fix: tools-call-simple-text now fails when tool returns isError: true#165
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Conversation
@lux999
@lux999lux999
commented
Feb 24, 2026

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Added an isError check to ToolsCallSimpleTextScenario, so the test tools-call-simple-text correctly fails when the tool returns an error result instead of a successful text response.
Motivation and Context
The test tools-call-simple-text was passing for servers that don't implement test_simple_text at all.

When an unknown tool is called, MCP frameworks return { isError: true, content: [{ type: "text", text: "Tool not found: ..." }] }. The existing assertions only checked for a non-empty text content item, which the "Tool not found" error message satisfies. The missing assertion was that result.isError must not be true.
How Has This Been Tested?
Verified against the existing everything-server reference implementation, which correctly implements test_simple_text and continues to pass. Confirmed that servers without test_simple_text now correctly fail the test.
Breaking Changes
Servers that were previously passing tools-call-simple-text without implementing test_simple_text will now correctly fail.
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
pcarleton
pcarleton
previously approved these changes
Mar 25, 2026
View reviewed changes
@pcarletonpcarleton
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LGTM, thanks!
@pcarleton
pcarleton
enabled auto-merge (squash)
March 25, 2026 12:10
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Mar 25, 2026

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npx https://pkg.pr.new/@modelcontextprotocol/conformance@165

commit: cd062a6

auto-merge was automatically disabled
April 19, 2026 20:13
Head branch was pushed to by a user without write access
alu
fix: pass empty arguments object in tools-call-simple-text scenario
3af5ac4
The reference everything-server's zod schema rejects `undefined` arguments
and requires at least `{}`, so omitting `arguments` caused the server to
return `isError: true` with a validation error. This went unnoticed under
the previous lenient check but is correctly flagged by the new `isError`
assertion. Matches the convention used by every other tool-call scenario
in this file.
@lux999
lux999force-pushed
the
fix/tools-call-simple-text-iserror-check
branch
from
04febed to
3af5ac4CompareApril 19, 2026 20:41
@lux999
lux999
commented
Apr 19, 2026

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Author
Hi @pcarleton, thanks for the approval!
Quick heads-up on the new commit: after merging main, CI caught one test failure. This scenario originally omitted arguments since they're not required for test_simple_text, but the upstream SDK server rejects undefined arguments against any inputSchema and returns isError: true - which the new check correctly flags. There's an upstream fix in typescript-sdk#1404 but it wasn't backported to 1.x - see typescript-sdk#1869.
I squashed a small workaround into the fix commit: pass arguments: {} explicitly, with an inline comment linking to the SDK issue. Matches the convention in the sibling tool-call scenarios. Happy to revisit if you'd prefer a different approach.
Thanks again!
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@lux999@pcarleton

, '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: tools-call-simple-text now fails when tool returns isError: true - #165
Open
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Open
fix: tools-call-simple-text now fails when tool returns isError: true#165
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Conversation
@lux999
@lux999lux999
commented
Feb 24, 2026

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Added an isError check to ToolsCallSimpleTextScenario, so the test tools-call-simple-text correctly fails when the tool returns an error result instead of a successful text response.
Motivation and Context
The test tools-call-simple-text was passing for servers that don't implement test_simple_text at all.

When an unknown tool is called, MCP frameworks return { isError: true, content: [{ type: "text", text: "Tool not found: ..." }] }. The existing assertions only checked for a non-empty text content item, which the "Tool not found" error message satisfies. The missing assertion was that result.isError must not be true.
How Has This Been Tested?
Verified against the existing everything-server reference implementation, which correctly implements test_simple_text and continues to pass. Confirmed that servers without test_simple_text now correctly fail the test.
Breaking Changes
Servers that were previously passing tools-call-simple-text without implementing test_simple_text will now correctly fail.
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
pcarleton
pcarleton
previously approved these changes
Mar 25, 2026
View reviewed changes
@pcarletonpcarleton
left a comment


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LGTM, thanks!
@pcarleton
pcarleton
enabled auto-merge (squash)
March 25, 2026 12:10
@pkg-pr-new
pkg-pr-newBot
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Mar 25, 2026

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npx https://pkg.pr.new/@modelcontextprotocol/conformance@165

commit: cd062a6

auto-merge was automatically disabled
April 19, 2026 20:13
Head branch was pushed to by a user without write access
alu
fix: pass empty arguments object in tools-call-simple-text scenario
3af5ac4
The reference everything-server's zod schema rejects `undefined` arguments
and requires at least `{}`, so omitting `arguments` caused the server to
return `isError: true` with a validation error. This went unnoticed under
the previous lenient check but is correctly flagged by the new `isError`
assertion. Matches the convention used by every other tool-call scenario
in this file.
@lux999
lux999force-pushed
the
fix/tools-call-simple-text-iserror-check
branch
from
04febed to
3af5ac4CompareApril 19, 2026 20:41
@lux999
lux999
commented
Apr 19, 2026

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Author
Hi @pcarleton, thanks for the approval!
Quick heads-up on the new commit: after merging main, CI caught one test failure. This scenario originally omitted arguments since they're not required for test_simple_text, but the upstream SDK server rejects undefined arguments against any inputSchema and returns isError: true - which the new check correctly flags. There's an upstream fix in typescript-sdk#1404 but it wasn't backported to 1.x - see typescript-sdk#1869.
I squashed a small workaround into the fix commit: pass arguments: {} explicitly, with an inline comment linking to the SDK issue. Matches the convention in the sibling tool-call scenarios. Happy to revisit if you'd prefer a different approach.
Thanks again!
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, '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: tools-call-simple-text now fails when tool returns isError: true - #165
Open
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Open
fix: tools-call-simple-text now fails when tool returns isError: true#165
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Conversation
@lux999
@lux999lux999
commented
Feb 24, 2026

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Added an isError check to ToolsCallSimpleTextScenario, so the test tools-call-simple-text correctly fails when the tool returns an error result instead of a successful text response.
Motivation and Context
The test tools-call-simple-text was passing for servers that don't implement test_simple_text at all.

When an unknown tool is called, MCP frameworks return { isError: true, content: [{ type: "text", text: "Tool not found: ..." }] }. The existing assertions only checked for a non-empty text content item, which the "Tool not found" error message satisfies. The missing assertion was that result.isError must not be true.
How Has This Been Tested?
Verified against the existing everything-server reference implementation, which correctly implements test_simple_text and continues to pass. Confirmed that servers without test_simple_text now correctly fail the test.
Breaking Changes
Servers that were previously passing tools-call-simple-text without implementing test_simple_text will now correctly fail.
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
pcarleton
pcarleton
previously approved these changes
Mar 25, 2026
View reviewed changes
@pcarletonpcarleton
left a comment


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LGTM, thanks!
@pcarleton
pcarleton
enabled auto-merge (squash)
March 25, 2026 12:10
@pkg-pr-new
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npx https://pkg.pr.new/@modelcontextprotocol/conformance@165

commit: cd062a6

auto-merge was automatically disabled
April 19, 2026 20:13
Head branch was pushed to by a user without write access
alu
fix: pass empty arguments object in tools-call-simple-text scenario
3af5ac4
The reference everything-server's zod schema rejects `undefined` arguments
and requires at least `{}`, so omitting `arguments` caused the server to
return `isError: true` with a validation error. This went unnoticed under
the previous lenient check but is correctly flagged by the new `isError`
assertion. Matches the convention used by every other tool-call scenario
in this file.
@lux999
lux999force-pushed
the
fix/tools-call-simple-text-iserror-check
branch
from
04febed to
3af5ac4CompareApril 19, 2026 20:41
@lux999
lux999
commented
Apr 19, 2026

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Author
Hi @pcarleton, thanks for the approval!
Quick heads-up on the new commit: after merging main, CI caught one test failure. This scenario originally omitted arguments since they're not required for test_simple_text, but the upstream SDK server rejects undefined arguments against any inputSchema and returns isError: true - which the new check correctly flags. There's an upstream fix in typescript-sdk#1404 but it wasn't backported to 1.x - see typescript-sdk#1869.
I squashed a small workaround into the fix commit: pass arguments: {} explicitly, with an inline comment linking to the SDK issue. Matches the convention in the sibling tool-call scenarios. Happy to revisit if you'd prefer a different approach.
Thanks again!
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2 participants

@lux999@pcarleton

, '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: tools-call-simple-text now fails when tool returns isError: true - #165
Open
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Open
fix: tools-call-simple-text now fails when tool returns isError: true#165
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Conversation
@lux999
@lux999lux999
commented
Feb 24, 2026

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Added an isError check to ToolsCallSimpleTextScenario, so the test tools-call-simple-text correctly fails when the tool returns an error result instead of a successful text response.
Motivation and Context
The test tools-call-simple-text was passing for servers that don't implement test_simple_text at all.

When an unknown tool is called, MCP frameworks return { isError: true, content: [{ type: "text", text: "Tool not found: ..." }] }. The existing assertions only checked for a non-empty text content item, which the "Tool not found" error message satisfies. The missing assertion was that result.isError must not be true.
How Has This Been Tested?
Verified against the existing everything-server reference implementation, which correctly implements test_simple_text and continues to pass. Confirmed that servers without test_simple_text now correctly fail the test.
Breaking Changes
Servers that were previously passing tools-call-simple-text without implementing test_simple_text will now correctly fail.
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
pcarleton
pcarleton
previously approved these changes
Mar 25, 2026
View reviewed changes
@pcarletonpcarleton
left a comment


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LGTM, thanks!
@pcarleton
pcarleton
enabled auto-merge (squash)
March 25, 2026 12:10
@pkg-pr-new
pkg-pr-newBot
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Mar 25, 2026

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Open in StackBlitz
npx https://pkg.pr.new/@modelcontextprotocol/conformance@165

commit: cd062a6

auto-merge was automatically disabled
April 19, 2026 20:13
Head branch was pushed to by a user without write access
alu
fix: pass empty arguments object in tools-call-simple-text scenario
3af5ac4
The reference everything-server's zod schema rejects `undefined` arguments
and requires at least `{}`, so omitting `arguments` caused the server to
return `isError: true` with a validation error. This went unnoticed under
the previous lenient check but is correctly flagged by the new `isError`
assertion. Matches the convention used by every other tool-call scenario
in this file.
@lux999
lux999force-pushed
the
fix/tools-call-simple-text-iserror-check
branch
from
04febed to
3af5ac4CompareApril 19, 2026 20:41
@lux999
lux999
commented
Apr 19, 2026

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Author
Hi @pcarleton, thanks for the approval!
Quick heads-up on the new commit: after merging main, CI caught one test failure. This scenario originally omitted arguments since they're not required for test_simple_text, but the upstream SDK server rejects undefined arguments against any inputSchema and returns isError: true - which the new check correctly flags. There's an upstream fix in typescript-sdk#1404 but it wasn't backported to 1.x - see typescript-sdk#1869.
I squashed a small workaround into the fix commit: pass arguments: {} explicitly, with an inline comment linking to the SDK issue. Matches the convention in the sibling tool-call scenarios. Happy to revisit if you'd prefer a different approach.
Thanks again!
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, '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: tools-call-simple-text now fails when tool returns isError: true - #165
Open
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Open
fix: tools-call-simple-text now fails when tool returns isError: true#165
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
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@lux999
@lux999lux999
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Feb 24, 2026

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Added an isError check to ToolsCallSimpleTextScenario, so the test tools-call-simple-text correctly fails when the tool returns an error result instead of a successful text response.
Motivation and Context
The test tools-call-simple-text was passing for servers that don't implement test_simple_text at all.

When an unknown tool is called, MCP frameworks return { isError: true, content: [{ type: "text", text: "Tool not found: ..." }] }. The existing assertions only checked for a non-empty text content item, which the "Tool not found" error message satisfies. The missing assertion was that result.isError must not be true.
How Has This Been Tested?
Verified against the existing everything-server reference implementation, which correctly implements test_simple_text and continues to pass. Confirmed that servers without test_simple_text now correctly fail the test.
Breaking Changes
Servers that were previously passing tools-call-simple-text without implementing test_simple_text will now correctly fail.
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
pcarleton
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Mar 25, 2026
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LGTM, thanks!
@pcarleton
pcarleton
enabled auto-merge (squash)
March 25, 2026 12:10
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npx https://pkg.pr.new/@modelcontextprotocol/conformance@165

commit: cd062a6

auto-merge was automatically disabled
April 19, 2026 20:13
Head branch was pushed to by a user without write access
alu
fix: pass empty arguments object in tools-call-simple-text scenario
3af5ac4
The reference everything-server's zod schema rejects `undefined` arguments
and requires at least `{}`, so omitting `arguments` caused the server to
return `isError: true` with a validation error. This went unnoticed under
the previous lenient check but is correctly flagged by the new `isError`
assertion. Matches the convention used by every other tool-call scenario
in this file.
@lux999
lux999force-pushed
the
fix/tools-call-simple-text-iserror-check
branch
from
04febed to
3af5ac4CompareApril 19, 2026 20:41
@lux999
lux999
commented
Apr 19, 2026

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Author
Hi @pcarleton, thanks for the approval!
Quick heads-up on the new commit: after merging main, CI caught one test failure. This scenario originally omitted arguments since they're not required for test_simple_text, but the upstream SDK server rejects undefined arguments against any inputSchema and returns isError: true - which the new check correctly flags. There's an upstream fix in typescript-sdk#1404 but it wasn't backported to 1.x - see typescript-sdk#1869.
I squashed a small workaround into the fix commit: pass arguments: {} explicitly, with an inline comment linking to the SDK issue. Matches the convention in the sibling tool-call scenarios. Happy to revisit if you'd prefer a different approach.
Thanks again!
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, '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: tools-call-simple-text now fails when tool returns isError: true - #165
Open
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Open
fix: tools-call-simple-text now fails when tool returns isError: true#165
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Conversation
@lux999
@lux999lux999
commented
Feb 24, 2026

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Added an isError check to ToolsCallSimpleTextScenario, so the test tools-call-simple-text correctly fails when the tool returns an error result instead of a successful text response.
Motivation and Context
The test tools-call-simple-text was passing for servers that don't implement test_simple_text at all.

When an unknown tool is called, MCP frameworks return { isError: true, content: [{ type: "text", text: "Tool not found: ..." }] }. The existing assertions only checked for a non-empty text content item, which the "Tool not found" error message satisfies. The missing assertion was that result.isError must not be true.
How Has This Been Tested?
Verified against the existing everything-server reference implementation, which correctly implements test_simple_text and continues to pass. Confirmed that servers without test_simple_text now correctly fail the test.
Breaking Changes
Servers that were previously passing tools-call-simple-text without implementing test_simple_text will now correctly fail.
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
pcarleton
pcarleton
previously approved these changes
Mar 25, 2026
View reviewed changes
@pcarletonpcarleton
left a comment


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LGTM, thanks!
@pcarleton
pcarleton
enabled auto-merge (squash)
March 25, 2026 12:10
@pkg-pr-new
pkg-pr-newBot
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Mar 25, 2026

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Open in StackBlitz
npx https://pkg.pr.new/@modelcontextprotocol/conformance@165

commit: cd062a6

auto-merge was automatically disabled
April 19, 2026 20:13
Head branch was pushed to by a user without write access
alu
fix: pass empty arguments object in tools-call-simple-text scenario
3af5ac4
The reference everything-server's zod schema rejects `undefined` arguments
and requires at least `{}`, so omitting `arguments` caused the server to
return `isError: true` with a validation error. This went unnoticed under
the previous lenient check but is correctly flagged by the new `isError`
assertion. Matches the convention used by every other tool-call scenario
in this file.
@lux999
lux999force-pushed
the
fix/tools-call-simple-text-iserror-check
branch
from
04febed to
3af5ac4CompareApril 19, 2026 20:41
@lux999
lux999
commented
Apr 19, 2026

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Author
Hi @pcarleton, thanks for the approval!
Quick heads-up on the new commit: after merging main, CI caught one test failure. This scenario originally omitted arguments since they're not required for test_simple_text, but the upstream SDK server rejects undefined arguments against any inputSchema and returns isError: true - which the new check correctly flags. There's an upstream fix in typescript-sdk#1404 but it wasn't backported to 1.x - see typescript-sdk#1869.
I squashed a small workaround into the fix commit: pass arguments: {} explicitly, with an inline comment linking to the SDK issue. Matches the convention in the sibling tool-call scenarios. Happy to revisit if you'd prefer a different approach.
Thanks again!
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@pcarletonpcarletonpcarleton left review comments

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@lux999@pcarleton

, '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: tools-call-simple-text now fails when tool returns isError: true - #165
Open
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Open
fix: tools-call-simple-text now fails when tool returns isError: true#165
lux999 wants to merge 3 commits into
modelcontextprotocol:mainfrom 
lux999:fix/tools-call-simple-text-iserror-check
Conversation
@lux999
@lux999lux999
commented
Feb 24, 2026

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Added an isError check to ToolsCallSimpleTextScenario, so the test tools-call-simple-text correctly fails when the tool returns an error result instead of a successful text response.
Motivation and Context
The test tools-call-simple-text was passing for servers that don't implement test_simple_text at all.

When an unknown tool is called, MCP frameworks return { isError: true, content: [{ type: "text", text: "Tool not found: ..." }] }. The existing assertions only checked for a non-empty text content item, which the "Tool not found" error message satisfies. The missing assertion was that result.isError must not be true.
How Has This Been Tested?
Verified against the existing everything-server reference implementation, which correctly implements test_simple_text and continues to pass. Confirmed that servers without test_simple_text now correctly fail the test.
Breaking Changes
Servers that were previously passing tools-call-simple-text without implementing test_simple_text will now correctly fail.
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
pcarleton
pcarleton
previously approved these changes
Mar 25, 2026
View reviewed changes
@pcarletonpcarleton
left a comment


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LGTM, thanks!
@pcarleton
pcarleton
enabled auto-merge (squash)
March 25, 2026 12:10
@pkg-pr-new
pkg-pr-newBot
commented
Mar 25, 2026

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Open in StackBlitz
npx https://pkg.pr.new/@modelcontextprotocol/conformance@165

commit: cd062a6

auto-merge was automatically disabled
April 19, 2026 20:13
Head branch was pushed to by a user without write access
alu
fix: pass empty arguments object in tools-call-simple-text scenario
3af5ac4
The reference everything-server's zod schema rejects `undefined` arguments
and requires at least `{}`, so omitting `arguments` caused the server to
return `isError: true` with a validation error. This went unnoticed under
the previous lenient check but is correctly flagged by the new `isError`
assertion. Matches the convention used by every other tool-call scenario
in this file.
@lux999
lux999force-pushed
the
fix/tools-call-simple-text-iserror-check
branch
from
04febed to
3af5ac4CompareApril 19, 2026 20:41
@lux999
lux999
commented
Apr 19, 2026

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Author
Hi @pcarleton, thanks for the approval!
Quick heads-up on the new commit: after merging main, CI caught one test failure. This scenario originally omitted arguments since they're not required for test_simple_text, but the upstream SDK server rejects undefined arguments against any inputSchema and returns isError: true - which the new check correctly flags. There's an upstream fix in typescript-sdk#1404 but it wasn't backported to 1.x - see typescript-sdk#1869.
I squashed a small workaround into the fix commit: pass arguments: {} explicitly, with an inline comment linking to the SDK issue. Matches the convention in the sibling tool-call scenarios. Happy to revisit if you'd prefer a different approach.
Thanks again!
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@pcarletonpcarletonpcarleton left review comments

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