Extend and maintain the app's MCP server — add tools for new or existing app capabilities, keep the CI parity check green, and work with the OAuth 2.1 layer. Use when adding or changing any business function or route (the parity test will demand MCP coverage), when writing MCP tools, when working on app/mcp/, the /mcp endpoint, OAuth routes, scopes, or the consent screen, or when the user mentions MCP, tools, or the parity check.
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Extend and maintain the app's MCP server — add tools for new or existing app capabilities, keep the CI parity check green, and work with the OAuth 2.1 layer. Use when adding or changing any business function or route (the parity test will demand MCP coverage), when writing MCP tools, when working on app/mcp/, the /mcp endpoint, OAuth routes, scopes, or the consent screen, or when the user mentions MCP, tools, or the parity check.
App MCP Server
Everything a human can do in the app is also doable through MCP tools, with identical authentication and authorization. The server is stateless, OAuth 2.1-protected, and its coverage is CI-enforced: app/mcp/parity.test.ts fails whenever a route-invoked business function has no MCP tool.
Architecture map
app/routes/mcp.ts — the Streamable HTTP endpoint (POST only). Anonymous requests (no Authorization header) are served the anonymous toolset; invalid/expired tokens get 401 + WWW-Authenticate; tokens must be audience-bound to ${baseUrl}/mcp.
app/mcp/context.server.ts — token → context bridge. Resolves the access token, loads the user, and builds the exact context object routes build (via buildContext in app/business/auth.server.tsx). Also exports withVenueRoles (see venue tools below).
app/mcp/server.server.ts — per-request MCP Server (low-level SDK API). tools/list filters the registry by scope × isAvailable(context); tools/call dispatches to the tool's execute and maps composable-functions Result failures to MCP isError content.
app/mcp/tool.ts — the McpTool type.
— one file per business domain, exporting .
app/mcp/tools/<domain>.server.ts
<domain>Tools: McpTool[]
app/mcp/registry.server.ts — aggregates every domain array. Accumulate-only; rebase conflicts resolve keep-both.
app/mcp/parity.test.ts + parity-exemptions.ts + pending-coverage.ts — the parity check (below).
A tool's execute is a single call to an existing app/business composable function with the real context object. Never re-implement business logic, never build a context by hand, never add authorization logic. The business function's applySchema context schema re-validates permissions and its queries stay scoped — the same three layers the app enforces. isAvailable only ever uses the shared predicates from app/business/auth.common.ts (hasLabPermission, hasVenuePermission, hasLabAccess).
The sole sanctioned exception is profile_whoami (app/mcp/tools/auth.server.ts): it projects three explicit context fields with no business function behind it. Do not add more exceptions.
Adding a tool
Follow app/mcp/tools/plans.server.ts as the canonical example:
{
name: 'plans_create',
description: 'Create a subscription plan with a name and a monthly price in reais.',
inputSchema: createPlanSchema, // ALWAYS the schema from <domain>.common.ts — never redefinedscope: 'lab',
wraps: ['plans.createPlan'], // module.functionName — feeds the parity testisAvailable: (context) =>hasLabPermission(context.currentLabRole, 'plans:manage'),
execute: (input, context) => plans.createPlan(input, context),
}
Conventions:
Name: snake_case, <domain>_<verb_phrase> in clear domain language (visits_check_in, reference_tables_create_range). No abbreviations.
Description: one outcome-oriented English sentence a client model can act on. Say what it does and what the key inputs mean when non-obvious.
Input schema: reuse the business function's input schema from the domain's .common.ts. If the function receives route params (e.g. planId, venueId) merged in by act/load, the tool's schema must include them — extend the base schema exactly like the business function's own schema does, or reuse the already-extended one.
Date inputs: a schema containing z.date() (or a date-coercing z.preprocess/z.union) cannot be a tool's inputSchema — z.toJSONSchema throws on it even in io: 'input' mode. Use isoDateSchema() from app/framework/schemas.ts (an ISO YYYY-MM-DD string transformed to a local-midnight Date) in the business function's input schema itself, so app and MCP share one shape.
Scope (consent-time restriction, layered on top of role authz): 'anonymous' (no token needed), 'profile', 'care', 'lab', 'venues'.
isAvailable mirrors the route's context getter: lab getters → hasLabPermission(context.currentLabRole, '<permission>'); getLabAccessContext → hasLabAccess(context.currentLabRole); customer surface → Boolean(context.currentCustomer); user surface → Boolean(context.currentUser); anonymous → () => true. Find the route's getter in the route file that invokes the function.
Register the domain array in registry.server.ts (one import + one spread).
Venue tools
The MCP context has no venue roles (they are per-venue). Venue-scoped tools fetch them per call with the shared helper — same query the app's getVenueOperateContext runs, same schema denial:
withVenueRoles(input, context) reads venueId from the input and returns the context with currentVenueRoles attached (empty when the user has no roles there — the business function's venueOperateContextSchema/refined variants then deny, exactly like the app). isAvailable for venue tools is (context) => Boolean(context.currentUser) — per-venue permission can only be checked at call time.
Anonymous tools
Only for capabilities the app serves without a session (checkout entry, magic-link request). The anonymous surface is exactly what the app serves logged-out — never more.
The parity check
pnpm run test:unit runs app/mcp/parity.test.ts, which extracts every business function invoked by app/routes/** (TypeScript compiler API) and asserts each is wrapped (some tool's wraps), exempted (parity-exemptions.ts, with a written reason — e.g. OAuth plumbing, Stripe webhook internals), or pending (pending-coverage.ts). It also fails on stale pending entries (already wrapped) and dangling wraps (function no routes invoke).
Adding an app capability? The parity test fails until you add the MCP tool (or a reasoned exemption). Add the tool in the same PR — that is the Definition of Done.
Covering pending functions? Remove them from pending-coverage.ts in the same commit that wraps them.
Exemptions are rare and must say why the function is not a user capability.
Testing tools
Use app/test/prelude.ts factories and call the helpers directly (see app/mcp/server.server.test.ts):
Denial: callTool with a context missing the permission (e.g. createUserCtxWithPermissions(['results:manage']) for a plans tool) → expect isError: true with the context schema's message. This proves the same-code-path guarantee.
Visibility: listTools with scopes/permissions combinations → tool present/absent.
Happy path: at least one representative call per domain proving input schema and result shape.
OAuth layer (rarely touched)
OAuth 2.1: dynamic client registration (RFC 7591), discovery (RFC 8414 + 9728), authorization-code + PKCE S256 (verifier checked constant-time at exchange; wrong verifier burns the single-use code), refresh rotation, all credentials SHA-256-hashed at rest. Scopes: profile care lab venues; a request whose scope string matches none of these is rejected as invalid_scope; omitted scope defaults to all four. Consent lives at /mcp/authorize (design-system screen, gated by getUserContext, so sign-in is the normal magic-link flow). Tokens are audience-bound: resource must equal ${baseUrl}/mcp or the endpoint rejects with invalid_audience. Keep every credential hashed, keep PKCE mandatory, and never introduce an in-memory session store — the endpoint is stateless by design.
