Protocol types for 2026-07-28: superset monolith, committed per-version packages, and wire-method maps#2849
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…s, and wire-method maps One public type set (mcp.types) covering every protocol revision through 2026-07-28; two per-version model packages that act as the schema-exact validating layer; and plain (method, version) maps with two-step parse functions. Version gating is data: key absence is the gate. Outbound serialization is the model dump, with the new 2026-07-28 result fields as ordinary serialized defaults. Includes a surface-to-monolith field-parity test that asserts every wire alias in either per-version package is carried by the monolith.
Vendor schema/2025-11-25.json and schema/2026-07-28.json (pinned to spec SHA 6d441518), restore scripts/gen_surface_types.py to regenerate both src/mcp/types/v* packages from them, and run --check in CI so the committed files cannot drift from the schemas.
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… generated-file pyright suppression
- Add validate_client_request/notification, validate_server_result to
types.methods (surface-only siblings of the parse_* functions)
- ServerRunner validates inbound requests/notifications against the
negotiated version's surface schema; custom methods fall through to
the registered params_type as before
- Handler results are validated against the surface schema after dump;
a spec-invalid result is logged and returns INTERNAL_ERROR to the client
- Map JSON-Schema format byte/uri/uri-template to plain str in codegen
(Base64Str and AnyUrl over-assert on annotation-only formats);
regenerate both surface packages
- Fix two test fixtures that built Tool(input_schema={}) without the
spec-required type field
- Document handler-result validation in migration.md
Generated surface types switch to extra="ignore" (with a per-version allow-list for spec-declared open types: Result, _meta, GetTaskPayloadResult, Tool input/output schemas, URLElicitationRequiredError data). The runner now serializes spec-method results by dumping the monolith model and re-dumping through the negotiated version's surface row, so 2026-only fields (resultType, ttlMs, cacheScope) never reach the wire on a pre-2026 session. - Monolith ttl_ms/cache_scope default to None; the SDK does not stamp a caching policy. EmptyResult.result_type stays None (deployed peer servers strict-validate ping responses). - Spec methods absent at the negotiated version reject with METHOD_NOT_FOUND even if a handler is registered; custom methods fall through unchanged. - Version fallback for pre-handshake/stateless is the literal 2025-11-25, not LATEST_PROTOCOL_VERSION. - Add serialize_server_result to types.methods; codegen drift-guard asserts the open-class substitution count. - Docstrings now say method-gating per version, shape per schema era.
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Overview
Three type sets:
mcp.types.v2025_11_25— full generated types for the 2025-11-25 schema; serves every version through 2025-11-25mcp.types.v2026_07_28— full generated types for the 2026-07-28 (draft) schemamcp.types(the monolith) — hand-maintained superset of both; this is the public APIThe per-version packages validate inbound payloads and shape outbound ones; the monolith types are what user code constructs and receives.
mcp.types.methodsholds(method, version)→ surface-type maps and the parse/validate/serialize functions.Generation
scripts/gen_surface_types.pyrunsdatamodel-codegenover vendored sha-pinnedschema/*.json, with a few mappings overridden (format: byte/uri/uri-template→str, since JSON-Schemaformatis annotation-only) andextra="ignore"everywhere except a per-version allow-list of spec-declared open types (_meta,Result,GetTaskPayloadResult,Toolinput/output schemas,URLElicitationRequiredError.data). CI regenerates with--checkand diffs.Server-side wiring
ServerRunnerconsults the maps:METHOD_NOT_FOUNDeven if a handler is registered. Custom methods skip the gate and use their registeredparams_typeas before.resultType,ttlMs,cacheScope) never reach a pre-2026 peer. A handler return that doesn't validate against the surface schema is logged and answered withINTERNAL_ERROR.ttlMs/cacheScopedefault toNoneon the monolith; the SDK does not stamp a caching policy. At 2026 (when negotiable) handlers will need to set them explicitly.resultTypedefaults to"complete"on concrete results and is stripped at pre-2026 by the sieve.SUPPORTED_PROTOCOL_VERSIONSis unchanged — 2026-07-28 is modeled, not yet negotiable. Client-side wiring is a follow-up.Breaking changes
Tool(inputSchema={})— missing"type": "object") now raises and the client receivesINTERNAL_ERROR. Documented indocs/migration.md.Types of changes
Checklist