Webmcpify

webmcpify — make any web app agent-ready, verifiably

You are running the webmcpify pipeline. It takes an existing web application and exposes its user-facing functionality as WebMCP tools (document.modelContext — a proposed web standard incubated in the W3C Web Machine Learning Community Group, currently a Chrome origin trial), so browser AI agents can operate the app through structured tool calls instead of guessing at the DOM.

DETECT ──▶ INVENTORY ──▶ [HUMAN GATE: manifest approval] ──▶ INTEGRATE ──▶ VERIFY ──▶ HEAL ──▶ AUDIT
              ▲  loop            per-area batches on big apps    ▲  loop      ▲ loop    ▲ loop
              └── per area                                       └── per manifest entry ──┘

Everything you need ships inside this skill directory: phase guides in references/, and vendorable code in templates/ (runtime, ambient types, JS variant, React JSX typings, verification spec). Never assume files exist outside the skill dir.

Out of scope (stop and say so): backend-only MCP servers (that's classic MCP, not WebMCP), automating third-party sites you don't control, and generic SEO work.

Invocation modes

The user may pass an argument (/webmcpify <mode> or plain words):

Any other text is scoping guidance (e.g. "only the checkout area", "read-only tools only").

Ground rules (non-negotiable, enforce in every phase)

1. Zero unrelated changes. Every diff hunk you produce must trace to a manifest entry or the recorded one-time setup. Never refactor, reformat, rename, or "improve" anything else — note problems in the report instead. Files that were already dirty at baseline (recorded in the manifest) are untouchable: never modify or revert them.
2. Read-only tools first. Mutations are tri-state: mutating: false, "client" (browser-local only: prefs, localStorage), or "server" (data leaves the browser). Server-mutating tools require explicit per-tool human approval recorded in the manifest; client-mutating tools may be approved as a batch at the gate. Never expose destructive, irreversible, or payment actions in a first integration.
3. The server is the only trust boundary. A tool's execute() may only call code paths the UI already uses (same endpoints, same validation, same auth). Never create new endpoints, never bypass existing checks, never put secrets in tools.
4. Spec-shaped and dependency-free. Register via document.modelContext.registerTool() with AbortSignal lifecycle (feature-detect the deprecated navigator.modelContext fallback). No third-party WebMCP runtime dependencies. Everything feature-detected: the app behaves identically in browsers without WebMCP.
5. Never toolautosubmit on state-changing forms — neither mutating: "client" nor "server". Only on pure read forms (search, filter, availability).
6. State lives in files, not in your context. Read/write .webmcpify/ constantly; assume your context can be wiped between any two steps. Write the manifest atomically (write manifest.json.tmp, then rename over manifest.json).
7. Commits are opt-in. Never commit unless the human chose a commit policy at the gate (see below). Without git or without permission, leave changes in the working tree and record progress in the manifest only.

Fresh, authoritative guidance

WebMCP is an evolving origin-trial API — the surface has already changed during the trial (testing API removed 2026-07; navigator → document). Before Phase 2, if network is available, pull Google's current official guides rather than relying on memory:

npx -y modern-web-guidance@latest retrieve "webmcp,agentic-forms,agentic-javascript-tools"

If offline, use references/integrate.md — but prefer the live guides when they conflict.

The state protocol — .webmcpify/ in the target repo

Resume rule: if manifest.json exists, resume — recompute nothing already recorded. Merge leftover shards FIRST: any existing areas/<id>.tools.json files are merged into the manifest (mark those areas inventoried, delete the shards) before redispatching any sub-agents. Then continue at pipeline.phase, the first pending area, or the first tool whose status is not terminal. Terminal statuses: verified, skipped, rejected.

Phase transitions (make the atomic manifest write the moment the condition holds):

• detect → inventory: app recorded, baselineSha/baselineDirty captured.
• inventory → gate: no area pending, completeness pass has run.
• gate → integrate: every discovered tool is approved/rejected, and commitPolicy + commitWebmcpifyDir are set.
• integrate → verify: no approved tools remain (each integrated or terminal), build green.
• verify → heal: verify loop visited every integrated tool and ≥1 is failed (none failed → straight to audit).
• heal → audit: no tool failed and post-heal full re-verify passed.
• audit → done: every hunk mapped-or-flagged, report.md finalized.

Manifest schema (Webmcpify Manifest v3):

{
  "webmcpify": 3,
  "app": { "stack": "react-vite", "typescript": true, "entry": "src/main.tsx",
           "baseUrl": "http://localhost:5173", "startCommand": "npm run dev",
           "authFixtures": {                    // how verify OBTAINS each session
             "member": { "obtain": "npm run seed:test-user, then sign in at /login",
                         "account": "member@example.test",
                         "env": ["TEST_MEMBER_PASSWORD"] }  // env var NAMES only — never secret values
           } },
  "pipeline": {
    "phase": "inventory",          // detect|inventory|gate|integrate|verify|heal|audit|done — transition rules above
    "setup": {                     // PATHS created/modified per one-time setup step ([] = not done yet)
      "runtimeVendored": ["src/webmcp/webmcpify.ts", "src/webmcp/webmcp.d.ts"],
      "harnessInstalled": [".webmcpify/webmcp.spec.ts"],
      "originTrialNoted": ["README.md"]
    },
    "baselineSha": "abc1234",      // HEAD at pipeline start; null if no git
    "baselineDirty": ["src/wip.ts"], // paths dirty at start — untouchable (ground rule 1)
    "commitPolicy": null,          // set at the gate: "commit-per-batch" | "no-commit"
    "commitWebmcpifyDir": null,    // set at the gate: commit .webmcpify/ itself? true | false
    "blockers": []                 // e.g. "app won't start locally: needs $API_KEY" — surfaced at the gate
  },
  "areas": [
    { "id": "checkout", "paths": ["src/features/checkout/"], "status": "pending" } // pending|inventoried
  ],
  "tools": [
    {
      "id": "create_ticket",
      "area": "tickets",
      "kind": "imperative",        // imperative | declarative
      "mutating": "server",        // false | "client" (browser-local only: prefs, localStorage) | "server" (data leaves the browser)
      "priority": 1,               // 1 = expose first; 2/3 = later waves
      "description": "Creates a new ticket in the currently open project.",
      "inputSchema": { /* JSON Schema */ },
      "annotations": { "readOnlyHint": false, "untrustedContentHint": false }, // verify asserts these on the enumerated tool
      "source": ["src/features/tickets/NewTicket.tsx:42"], // the UI code path it wraps
      "route": "/projects/demo/tickets",                    // where verify navigates
      "auth": ["role:member"],     // "none" | "session" | ["role:<name>", ...] — keys into app.authFixtures; verify runs once per listed role
      "examples": { "valid": { "title": "Test ticket" }, "invalid": {} },
                                   // invalid: null ONLY for readOnlyHint tools with no/empty params —
                                   // verify then asserts dual-outcome: rejects OR resolves with no side effect
      "expect": { "result": "created", "navigation": null, "ui": "new row appears in the ticket list" },
                                   // exactly one of result|navigation: result = substring of the resolved string;
                                   // navigation = destination URL/pattern when executeTool resolves null (it navigated)
      "cleanup": "delete the created ticket via the UI's own delete path (test data only)", // required for mutating:"server", recommended for "client"
      "status": "discovered",      // discovered|approved|rejected*|integrated|verified*|failed|skipped*  (* = terminal)
      "approval": null,            // server-mutating tools, once approved: { "note": "...", "at": "2026-07-12",
                                   //   "productionSideEffect": null } — set only when verification unavoidably
                                   //   causes a real production effect (see VERIFY: production side-effect policy)
      "attempts": 0,               // heal-fix cycles; the triggering verify failure is attempt 0
      "batchCommit": null,         // sha under commit-per-batch — lands in the manifest one commit LATER
      "notes": ""
    }
  ],
  "log": [ "2026-07-12 inventory: area checkout done, 4 candidates" ]
}

v2→v3 migration: resuming a "webmcpify": 2 manifest migrates in place on first write — auth string → array; setup booleans → path arrays (false → []; true → recover paths from git/log, else null = done-but-unrecorded, audit treats those files flag-only); mutating: true → "server"; add annotations (defaults from the inventory table), blockers: [], commitWebmcpifyDir: null, expect.navigation: null; then bump to 3.

Phase 0 — DETECT

Identify stack, build + dev-server commands, TypeScript or not, auth model (including how verify obtains each test session → app.authFixtures), test setup, and how the app starts locally; record under app. Record the git baseline: pipeline.baselineSha = current HEAD and pipeline.baselineDirty = git status --porcelain paths (both null/[] without git). If the app cannot be started locally, append the blocker to pipeline.blockers — integration may proceed, but verification will be blocked and this must be surfaced at the gate. Details: references/inventory.md.

Phase 1 — INVENTORY (loop; scales to any size)

Never map a large codebase in one pass.

1. Area map first (cheap, structural): enumerate routes/views/feature modules from the router config, pages directory, or navigation — without reading implementation files. Write every area to areas with "pending".
2. Inventory loop — one area per iteration: deep-read only that area's files; draft a candidate tool per user action (conventions, tool-count budget, and overlap rules: references/inventory.md) with ALL manifest fields filled, including route, auth, annotations, examples, expect, and cleanup (required for mutating: "server", recommended for "client") — the verify phase runs from these fields alone. Append as "discovered", mark the area "inventoried", write the manifest, repeat.
   • Sub-agent fan-out: sub-agents never write manifest.json. Each writes only its own areas/<id>.tools.json shard — schema { "webmcpifyShard": 3, "area": "<id>", "tools": [ /* full v3 tool entries */ ] }, written atomically (tmp + rename). You (the coordinator) merge shards into the manifest sequentially, then delete them; on resume, merge existing shards FIRST before redispatching (Resume rule).
3. Exit: no pending areas remain, plus one completeness pass — walk the app's navigation and ask "is any visible user action missing?"

GATE — manifest approval (the one main checkpoint)

Present the manifest compactly (id, area, kind, mutating, priority, one-line description) — per-area batches on large apps. Ask the human to decide, in one exchange where possible:

1. Which tools are approved vs rejected (rejected is terminal — rejected tools are excluded from every later phase and from exit conditions). mutating: "server" tools need individual acknowledgment → record in approval; mutating: "client" tools may be approved as a batch.
2. Commit policy: commit-per-batch (each integration batch committed, revertable — recommended on a clean baseline) or no-commit (leave changes uncommitted for the human to review/commit) → pipeline.commitPolicy. Also whether .webmcpify/ itself should be committed (recommended: yes — it documents the integration) → pipeline.commitWebmcpifyDir.
3. Every entry in pipeline.blockers (e.g. app won't start). If verifying a tool will unavoidably cause a real production side effect (e.g. a mailer with an Origin-allow-listed endpoint), get that approved HERE and record it in the tool's approval.productionSideEffect — see VERIFY.

Apply references/security.md to every mutating tool before presenting.

Phase 2 — INTEGRATE (loop)

One-time setup first — record the created/modified file paths in pipeline.setup (e.g. runtimeVendored: ["src/webmcp/webmcpify.ts", ...]): vendor the runtime from this skill's templates/ (webmcpify.ts, or webmcpify.js for non-TS projects, plus webmcp.d.ts for TS and webmcp-jsx.d.ts for React TSX — keep the full MIT header; see references/runtime.md) and note the origin-trial/flag requirement in the target README (originTrialNoted). Then loop:

1. Pick the next batch of approved tools — one area or ≤5 tools.
2. Implement per references/integrate.md: declarative attributes for standard HTML forms (including framework-rendered and fetch-intercepted ones); imperative registration via the vendored runtime for non-form or controlled-state actions.
3. Build + typecheck; fix only what the batch broke.
4. Mark tools "integrated", write the manifest. Under commit-per-batch: require a clean index before staging (unrelated staged changes → stop and surface); stage only the batch's files by path — never git add -A, -u, ., or commit -a; commit feat(webmcp): expose <ids> (webmcpify). The commit sha lands in batchCommit on the next manifest write — one commit later (the manifest can't contain its own commit's sha). Never amend a previous batch commit.
5. Repeat until no approved tools remain.

Phase 3 — VERIFY (loop)

Set up once from templates/webmcp.spec.ts per references/verify.md (real headed Chrome; production getTools()/executeTool() surface with legacy fallback probe). Then loop over every integrated tool, using its manifest route, auth, examples, expect, and annotations fields:

• assert the tool is registered with the expected schema (enumerated inputSchema is a stringified JSON Schema — parse before comparing) and the manifest annotations;
• execute the valid example (mutating tools: dev/test data only, then run cleanup) and one invalid example (invalid: null zero-param read tools: dual-outcome assertion — see references/verify.md);
• assert on the returned result and the resulting UI state per expect (a UI delta, or expect.navigation when execution resolves null).

Pass → "verified". Fail → "failed" + failure note. Role-scoped tools: run the loop once per role listed in auth, signing in via the matching app.authFixtures entry.

Production side-effect policy — when a tool's verification unavoidably causes a real production effect (e.g. an email actually sent), ALL THREE are required: (1) the human approved it at the gate, recorded in approval.productionSideEffect; (2) every test payload is marked [webmcpify verification]; (3) the effect is listed in report.md. Without the recorded approval, don't execute the live path — mark the tool skipped with a blocker note.

Phase 4 — HEAL (loop)

While any tool is "failed": diagnose via references/heal.md, fix only that tool's integration — implementation-only fixes; if the fix would change the approved contract (schema, description, mutating class, annotations, expect), go back to the gate for re-approval instead of silently changing the manifest. The triggering verify failure is attempt 0; increment attempts per fix cycle and re-verify. At attempts = 3 → "skipped" with a clear blocker note (an explicit escalation to the human, not a silent drop). Never widen the diff or fake a pass. After healing, re-run verification once for all tools with status integrated or verified (healing one tool can break another — scope collisions).

Exit: every tool is verified, skipped, or rejected; build green.

Final — AUDIT + report

1. Diff audit (flag-only, never auto-revert): collect the pipeline's changes — git diff <baselineSha>..HEAD plus the index and untracked files under commit-per-batch, or the working tree + index + untracked under no-commit. Every hunk must map to a manifest entry or a recorded pipeline.setup path. An unmapped hunk → flag it in the report with file/line and a suggested disposition; never revert anything yourself. A hunk in a baselineDirty file → untouchable, flag only. Without a baselineSha, audit the files named in manifest source fields and pipeline.setup paths (setup entries recorded as null by the v2→v3 migration: fall back to flag-only for those files).
2. Finalize .webmcpify/report.md: tool coverage per area, skipped/rejected tools with reasons, security notes (which mutating tools exist, what guards them, any recorded production side effects), how to test manually (flag, DevTools WebMCP pane, inspector extension), and every blocker that needs a human.
3. Tell the human: what's exposed, what's skipped and why, and how to try it.

References (read on demand, not upfront)

• references/inventory.md — area mapping, naming/schema conventions, budgets/overlap
• references/integrate.md — declarative + imperative patterns per stack
• references/runtime.md — vendoring + wiring the templates/ runtime
• references/verify.md — harness setup: flags, surfaces, Playwright/Puppeteer, evals
• references/heal.md — failure taxonomy → fixes
• references/security.md — the security checklist (apply before the gate and at audit)