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WebMCP audit fixes: spec page corrections, typed tool defs, budgets, evals - #261
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…evals
Spec page (agent-readiness/webmcp.md):
- consequentialHint, not destructiveHint (not a WebMCP annotation)
- drop mode: 'summarize' (not in the spec)
- verification: execute() resolves strings, not MCP { content: [...] }
- document untrustedContentHint + debugging, opt-in-only rule
- summary: document.modelContext is the current surface
- changelog entry added
Implementation (src/lib/webmcp.ts):
- tool metadata is now typed data checked against webmcp-types at build
time (new devDependency); helpers/execute emitted via Function.toString()
- list_topics: paginated (page/page_size, default 10) instead of dumping
all 177 topics (~53k chars)
- get_topic: offset/limit line paging with a continuation hint instead of
dumping up to ~12k chars
- registerTool() awaited per tool; rejections warn instead of unhandled
- execute() forwards the AbortSignal to fetch()
- titles added to all five tools
- structured error payloads { error, code, retryable?, suggestion? }
- removed annotations: { readOnlyHint: false } from the UI tools
(annotations are strictly opt-in; omission means false)
Also:
- webmcp.schema.json (generated from the built bundle via
scripts/emit-webmcp-schema.mjs, new npm run webmcp:schema) and
webmcp.evals.json (11 cases in the Chrome Labs evals format) for
npx webmcp-evals local -t webmcp.schema.json -e webmcp.evals.json
- /mcp page documents the browser WebMCP tools
- eslint override for the verbatim-emitted helpers (repo precedent:
BaseLayout byte-frozen script)
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Audited our WebMCP implementation against the current spec (webmcp-types) and the Chrome Labs review checklist.
Spec page (
agent-readiness/webmcp.md, + changelog entry):consequentialHint, notdestructiveHint(not a WebMCP annotation)mode: 'summarize' (not in the spec)execute()can resolve any JSON-serialisable value;executeTool()serialises it, and an MCP{ content: [...] }envelope is not requireduntrustedContentHint+debugging, and the opt-in-only ruledocument.modelContextas the current surfaceImplementation (
src/lib/webmcp.ts):webmcp-typesat build time (new devDependency) — a renamed annotation is now a build error; helpers/execute are emitted verbatim viaFunction.toString()list_topics: paginated (page/page_size, default 10) instead of dumping all 177 topics (~53k chars, 35x the recommended budget)get_topic:offset/limitline paging with a continuation hint instead of dumping up to ~12k charsregisterTool()awaited per tool; rejections warn instead of surfacing as unhandled rejectionsexecute()forwards theAbortSignalto topic fetches; the shared manifest fetch is independent, with cancellation handled per callertitleon all five tools; structured errors{ error, code, retryable?, suggestion? }; removed the forbiddenreadOnlyHint: falsedeclarations on the UI toolsAlso:
webmcp.schema.json(generated from the built bundle viascripts/emit-webmcp-schema.mjs, newnpm run webmcp:schema) +webmcp.evals.json(11 cases in the Chrome Labs evals format) — runnable vianpx webmcp-evals local -t webmcp.schema.json -e webmcp.evals.json/mcppage now documents the browser WebMCP toolsVerified:
astro checkclean, eslint clean, full build +check-integritypass, and a stubbed-browser harness confirmed unchanged behavior on all previously-working paths (search ranking, short-page reads, checklist navigation) plus the new pagination/truncation/structured-error/signal paths.Regression coverage: five tests exercise the generated browser bundle for independent cancellation, already-aborted calls, cancelled topic reads, network retries, and listener cleanup. CI runs them after the build. Local build, Astro check, lint, formatting, and Agent Skill integrity checks pass.