alpha.3: CfWorkerJsonSchemaValidator and AjvJsonSchemaValidator declared in types but missing from runtime index.mjs export

[morluto]

Bug

In @modelcontextprotocol/server@2.0.0-alpha.3, CfWorkerJsonSchemaValidator and AjvJsonSchemaValidator are declared in the type declarations (dist/index.d.mts) and listed in the export type statement, but are missing from the runtime dist/index.mjs export. This causes a runtime SyntaxError when importing them from the package root.

Package version

@modelcontextprotocol/server@2.0.0-alpha.3

Reproduction

import { CfWorkerJsonSchemaValidator } from "@modelcontextprotocol/server";
const validator = new CfWorkerJsonSchemaValidator();

Results in:

SyntaxError: Export named 'CfWorkerJsonSchemaValidator' not found in module '.../dist/index.mjs'.

The same happens with AjvJsonSchemaValidator.

Evidence

Type declarations (dist/index.d.mts) — both are present

import { t as AjvJsonSchemaValidator } from "./ajvProvider-DZ_siXcF.mjs";
import { t as CfWorkerJsonSchemaValidator } from "./cfWorkerProvider-DUhk5Ewx.mjs";

export { ..., AjvJsonSchemaValidator, ..., CfWorkerJsonSchemaValidator, CfWorkerSchemaDraft, ... };

Runtime (dist/index.mjs) — both are absent

export { BAGGAGE_META_KEY, CLIENT_CAPABILITIES_META_KEY, ..., fromJsonSchema, getDisplayName, ..., validateHostHeader };
// No CfWorkerJsonSchemaValidator, no AjvJsonSchemaValidator

Subpath exports work correctly

The package.json exports field includes subpath entries that DO export them at runtime:

{
  "./validators/ajv": {
    "types": "./dist/validators/ajv.d.mts",
    "import": "./dist/validators/ajv.mjs"
  },
  "./validators/cf-worker": {
    "types": "./dist/validators/cfWorker.d.mts",
    "import": "./dist/validators/cfWorker.mjs"
  }
}

// dist/validators/cfWorker.mjs
import { t as CfWorkerJsonSchemaValidator } from "../cfWorkerProvider-BrJKpSFH.mjs";
export { CfWorkerJsonSchemaValidator };

So the classes exist and are exported via subpaths — the main index.mjs bundle just forgot to re-export them.

Workaround

Import from the subpath export instead of the package root:

import { CfWorkerJsonSchemaValidator } from "@modelcontextprotocol/server/validators/cf-worker";
import { AjvJsonSchemaValidator } from "@modelcontextprotocol/server/validators/ajv";

Expected behavior

Either:

1. Re-export CfWorkerJsonSchemaValidator and AjvJsonSchemaValidator from dist/index.mjs (matching the type declarations), or
2. Remove them from the dist/index.d.mts export list if the intent is to only expose them via subpath exports.

Option 1 is preferable since the type declarations already promise these exports from the root, and consumers importing from @modelcontextprotocol/server will expect them to be available at runtime.

[fuleinist]

I have a fix ready on my fork: fuleinist#1

Root cause: \packages/server/src/index.ts\ didn't re-export \AjvJsonSchemaValidator, \CfWorkerJsonSchemaValidator, or \CfWorkerSchemaDraft\ — so the runtime bundle omitted them even though the type declarations already listed them.

Fix: Added 3 re-export lines to \packages/server/src/index.ts:

• \export { Ajv, addFormats, AjvJsonSchemaValidator } from '@modelcontextprotocol/core-internal/validators/ajv'\
• \export type { CfWorkerSchemaDraft } from '@modelcontextprotocol/core-internal/validators/cfWorker'\
• \export { CfWorkerJsonSchemaValidator } from '@modelcontextprotocol/core-internal/validators/cfWorker'\

Subpath imports (@modelcontextprotocol/server/validators/ajv, @modelcontextprotocol/server/validators/cf-worker) are unchanged.

@felixweinberger or any maintainer — could you pull this in? The repo appears to restrict cross-fork PRs.

[felixweinberger]

Thanks for the report - taking a look

[mcp-claude]

reproduces on the published alpha.3 exactly, and the same class mismatch is present on main (d000de8) via the new CJS declaration output — dist/index.d.cts re-exports AjvJsonSchemaValidator, CfWorkerJsonSchemaValidator, CfWorkerSchemaDraft without a type qualifier while dist/index.cjs omits them, so .cts consumers compile clean and hit TypeError: ... is not a constructor at runtime. Source is export type at packages/core-internal/src/exports/public/index.ts:136-137; tsdown preserves the qualifier in the .d.mts pipeline on main but strips it in .d.cts (and stripped it in the alpha.3 .d.mts too). Workaround is the subpath import.

Right fix per the comment in that file (and matching the maintainer sketch at 7e8ad10 on fweinberger/packaging-dts-resolve) is to drop the three type re-exports from the public barrel entirely — the runtime classes stay reachable via @modelcontextprotocol/{client,server}/validators/{ajv,cf-worker} and the v1→v2 codemod already rewrites to those.

ESM repro against published alpha.3

package.json:

{
  "name": "repro-2391-alpha3",
  "type": "module",
  "dependencies": {
    "@modelcontextprotocol/server": "2.0.0-alpha.3"
  }
}

repro.mjs:

import { CfWorkerJsonSchemaValidator } from "@modelcontextprotocol/server";
console.log(typeof CfWorkerJsonSchemaValidator);

$ node repro.mjs
file://.../repro.mjs:1
import { CfWorkerJsonSchemaValidator } from "@modelcontextprotocol/server";
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: The requested module '@modelcontextprotocol/server' does not provide an export named 'CfWorkerJsonSchemaValidator'

Same shape for AjvJsonSchemaValidator. dist/index.d.mts line 2397 lists both without type while dist/index.mjs has zero references.

CJS repro against current main (d000de8) after `pnpm build:all`

repro-cjs.cts:

import { CfWorkerJsonSchemaValidator, AjvJsonSchemaValidator } from "@modelcontextprotocol/server";
const cf = new CfWorkerJsonSchemaValidator();
const ajv = new AjvJsonSchemaValidator();
console.log(cf, ajv);

tsconfig.json:

{
  "compilerOptions": {
    "target": "es2022",
    "module": "node16",
    "moduleResolution": "node16",
    "strict": true,
    "skipLibCheck": true,
    "outDir": "dist"
  },
  "include": ["repro-cjs.cts"]
}

$ npx tsc          # compiles clean — .d.cts declares them as runtime exports
$ node dist/repro-cjs.cjs
.../dist/repro-cjs.cjs:5
const cf = new server_1.CfWorkerJsonSchemaValidator();
           ^
TypeError: server_1.CfWorkerJsonSchemaValidator is not a constructor

dist/index.d.cts re-exports AjvJsonSchemaValidator, ..., CfWorkerJsonSchemaValidator, CfWorkerSchemaDraft with no type qualifier; dist/index.cjs has zero references. dist/index.d.mts on the same build correctly writes type AjvJsonSchemaValidator, ..., type CfWorkerJsonSchemaValidator, type CfWorkerSchemaDraft, so .mts consumers get TS1362 at the call site instead of a runtime crash.

code path

packages/core-internal/src/exports/public/index.ts:134-137:

// Validator providers are type-only here — import the runtime classes from the explicit
// `@modelcontextprotocol/{client,server}/validators/{ajv,cf-worker}` subpaths to customise.
export type { AjvJsonSchemaValidator } from '../../validators/ajvProvider';
export type { CfWorkerJsonSchemaValidator, CfWorkerSchemaDraft } from '../../validators/cfWorkerProvider';

packages/server/src/index.ts:91 re-exports via export * from '@modelcontextprotocol/core-internal/public'. The bundler collapses that into the barrel export at dist/index.d.{mts,cts}; the .d.cts path drops the type qualifiers for these three, which is what puts the runtime and types out of sync.

suggested fix

// packages/core-internal/src/exports/public/index.ts
- // Validator providers are type-only here — import the runtime classes from the explicit
- // `@modelcontextprotocol/{client,server}/validators/{ajv,cf-worker}` subpaths to customise.
- export type { AjvJsonSchemaValidator } from '../../validators/ajvProvider';
- export type { CfWorkerJsonSchemaValidator, CfWorkerSchemaDraft } from '../../validators/cfWorkerProvider';
+ // Validator provider classes are NOT re-exported here (not even as `type`): the bundler
+ // drops `type` qualifiers on re-exports in the .d.cts pipeline, producing a runtime-shaped
+ // declaration whose backing symbol is missing from the .cjs (and, historically for
+ // alpha.3, the .mjs). Consumers should import them from
+ // `@modelcontextprotocol/{client,server}/validators/{ajv,cf-worker}`.

test to verify: greps the final export { ... } block of both dist/index.d.mts and dist/index.d.cts for AjvJsonSchemaValidator / CfWorkerJsonSchemaValidator / CfWorkerSchemaDraft, asserts none of the three appear. Fails on unfixed builds (.d.mts still lists type X, .d.cts had bare X), passes after the source change + rebuild. Runs alongside the existing barrelClean.test.ts suite. Full workspace pnpm -r test (excluding the integration CF-worker suite, which is flaky here independent of this change) and pnpm typecheck:all both stay green.

[morluto]

Opened a narrow draft PR for the current CJS declaration/runtime mismatch: #2432.\n\nThe fix keeps the validator provider classes on the documented validator subpaths and removes them from the client/server root declaration barrels, so CJS consumers fail at type-check time instead of compiling root imports that resolve to undefined at runtime.