GET handler serving HTML, updated manifest format

[JReinhold]

This PR adds a GET handler to /mcp in @storybook/addon-mcp that shows the addon is successfully running. When component manifests exists, it automatically redirects to human readable component manifests. See storybookjs/storybook#32882

Recording of the experience of visiting /mcp now:

mcp-het.mp4

It also updates the manifest format to account for errors and missing snippets. See storybookjs/storybook#32855

[changeset-bot]

🦋 Changeset detected

Latest commit: 51eea40

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@storybook/addon-mcp	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[codecov]

Bundle Report

Changes will increase total bundle size by 3.74kB (11.03%) ⬆️⚠️, exceeding the configured threshold of 5%.

Bundle name	Size	Change
@storybook/mcp-esm	20.0kB	692 bytes (3.58%) ⬆️
@storybook/addon-mcp-esm	17.62kB	3.04kB (20.89%) ⬆️⚠️

Affected Assets, Files, and Routes:

view changes for bundle: @storybook/addon-mcp-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
preset.js	3.04kB	17.62kB	20.89% ⚠️

Files in preset.js:

• ./src/types.ts → Total Size: 614 bytes

• ./src/preset.ts → Total Size: 3.19kB

• ./src/mcp-handler.ts → Total Size: 3.74kB

• ./src/tools/is-manifest-available.ts → Total Size: 359 bytes

view changes for bundle: @storybook/mcp-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
index.js	90 bytes	13.22kB	0.69%
index.d.ts	602 bytes	6.78kB	9.75% ⚠️

Files in index.js:

• ./src/utils/format-manifest.ts → Total Size: 2.71kB

• ./src/types.ts → Total Size: 738 bytes

[codecov]

Codecov Report

❌ Patch coverage is 27.50000% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.91%. Comparing base (3191cd4) to head (51eea40).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
packages/addon-mcp/src/preset.ts	0.00%	26 Missing ⚠️
packages/mcp/src/utils/format-manifest.ts	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #50      +/-   ##
==========================================
- Coverage   84.50%   81.91%   -2.59%     
==========================================
  Files          14       15       +1     
  Lines         813      846      +33     
  Branches      157      159       +2     
==========================================
+ Hits          687      693       +6     
- Misses        118      145      +27     
  Partials        8        8              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[pkg-pr-new]

npm i https://pkg.pr.new/@storybook/addon-mcp@50

npm i https://pkg.pr.new/@storybook/mcp@50

commit: 51eea40

[Copilot]

Pull Request Overview

This PR updates the component manifest format to include a required path field, adds an optional error field, makes several fields truly optional (switching from exactOptional to optional), and introduces a GET handler for the /mcp endpoint that serves an HTML page with conditional redirection to the component manifest viewer.

Key changes:

• Required path field added to ComponentManifest schema and all test fixtures
• Changed from v.exactOptional() to v.optional() for various manifest fields
• Added optional error field to BaseManifest for error reporting
• Made Example.snippet optional and added guard to skip examples without snippets
• Introduced GET handler for /mcp that serves HTML to browsers and plain text to API clients
• Extracted isManifestAvailable utility function for reusability

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
packages/mcp/src/types.ts	Updated schema to add required path field, optional error field, and changed exactOptional to optional
packages/mcp/src/utils/format-manifest.ts	Added guard to skip examples without snippets
packages/mcp/src/utils/format-manifest.test.ts	Added path field to all test fixtures
packages/mcp/src/utils/get-manifest.test.ts	Added path field to test fixtures and improved formatting
packages/mcp/fixtures/*.fixture.json	Added path field to all component fixtures
packages/addon-mcp/src/tools/is-manifest-available.ts	Extracted utility function for checking manifest availability
packages/addon-mcp/src/preset.ts	Changed to async function, added GET handler for /mcp with HTML response and conditional redirect
packages/addon-mcp/src/mcp-handler.ts	Refactored to use extracted isManifestAvailable utility
packages/addon-mcp/CHANGELOG.md	Added changelog entries for versions 0.0.1-0.0.5
CHANGELOG.md	Removed duplicate changelog content (moved to package-specific file)
.changeset/*.md	Added changesets for manifest format update and GET handler addition

[shilman]

I imagine we'll want to redesign this but this is a great first iteration.

Longer term I worry that people might not know what the component manifest is and so it might be better to have a list of toolsets and statuses, rather than a redirect:

Dev [description] [disabled]
Docs [description] [view manifest]

[JReinhold]

Longer term I worry that people might not know what the component manifest is and so it might be better to have a list of toolsets and statuses, rather than a redirect:

Dev [description] [disabled]
Docs [description] [view manifest]

Yeah I can see how that makes sense. I'd want to avoid duplication between this page and the documentation (to avoid getting them out of sync), so we should try and link out to the docs on the matter as much as possible.