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@modelcontextprotocol/client 2.0.0-alpha.2 is missing peer dependency declaration for @cfworker/json-schema #2143
Description
Describe the bug
Application using @modelcontextprotocol/client dependency fails to import the Client at runtime due to missing @cfworker/json-schema. Works with 1.x @modelcontextprotocol/sdk
> node --version
v24.13.0
> npm run start
> my-service@1.0.0 start
> node dist/index.js
node:internal/modules/package_json_reader:316
throw new ERR_MODULE_NOT_FOUND(packageName, fileURLToPath(base), null);
^
Error [ERR_MODULE_NOT_FOUND]: Cannot find package '@cfworker/json-schema' imported from C:\repos\my-service\node_modules\@modelcontextprotocol\client\dist\src-RIHfgPRm.mjs
at Object.getPackageJSONURL (node:internal/modules/package_json_reader:316:9)
at packageResolve (node:internal/modules/esm/resolve:768:81)
at moduleResolve (node:internal/modules/esm/resolve:858:18)
at defaultResolve (node:internal/modules/esm/resolve:990:11)
at #cachedDefaultResolve (node:internal/modules/esm/loader:718:20)
at #resolveAndMaybeBlockOnLoaderThread (node:internal/modules/esm/loader:735:38)
at ModuleLoader.resolveSync (node:internal/modules/esm/loader:764:52)
at #resolve (node:internal/modules/esm/loader:700:17)
at ModuleLoader.getOrCreateModuleJob (node:internal/modules/esm/loader:620:35)
at ModuleJob.syncLink (node:internal/modules/esm/module_job:143:33) {
code: 'ERR_MODULE_NOT_FOUND'
}
Node.js v24.13.0
Manually installing @cfworker/json-schema as dependency solves this issue.
To Reproduce
Steps to reproduce the behavior:
npm install --save @modelcontextprotocol/clientnode -e "import { Client } from '@modelcontextprotocol/client';"
Expected behavior
All peer dependencies for library should be installed automatically.
Logs
> node -e "import { Client } from '@modelcontextprotocol/client';"
node:internal/modules/package_json_reader:316
throw new ERR_MODULE_NOT_FOUND(packageName, fileURLToPath(base), null);
^
Error [ERR_MODULE_NOT_FOUND]: Cannot find package '@cfworker/json-schema' imported from C:\repos\my-service\node_modules\@modelcontextprotocol\client\dist\src-RIHfgPRm.mjs
at Object.getPackageJSONURL (node:internal/modules/package_json_reader:316:9)
at packageResolve (node:internal/modules/esm/resolve:768:81)
at moduleResolve (node:internal/modules/esm/resolve:858:18)
at defaultResolve (node:internal/modules/esm/resolve:990:11)
at #cachedDefaultResolve (node:internal/modules/esm/loader:718:20)
at #resolveAndMaybeBlockOnLoaderThread (node:internal/modules/esm/loader:735:38)
at ModuleLoader.resolveSync (node:internal/modules/esm/loader:764:52)
at #resolve (node:internal/modules/esm/loader:700:17)
at ModuleLoader.getOrCreateModuleJob (node:internal/modules/esm/loader:620:35)
at ModuleJob.syncLink (node:internal/modules/esm/module_job:143:33) {
code: 'ERR_MODULE_NOT_FOUND'
}
Activity
he-yufeng commentedon May 22, 2026
I checked this against the published alpha.2 package and current main. The published package still reproduces the failure because dist/index.mjs imports a shared chunk that statically imports @cfworker/json-schema. Current main appears to have already fixed the root import path: after rebuilding packages/client, importing ./packages/client/dist/index.mjs succeeds and the root bundle no longer has a static @cfworker/json-schema import.
So this looks like it may be fixed by the current source and needs the next alpha publish rather than another code change. I did not open a duplicate PR.
kagura-chen commentedon May 25, 2026
I'd like to take this one.
The root cause:
tsdownbundles@modelcontextprotocol/coreinto the client (noExternal: ['@modelcontextprotocol/core']). Thevalidators/cfWorkerentry point imports@cfworker/json-schemathrough core, and tsdown creates a shared chunk (src-RIHfgPRm.mjs) that mixes both the main barrel code and the cfWorker validator. Sinceindex.mjsloads from this shared chunk, the@cfworker/json-schemaimport fires eagerly — even when users only import the base client.Proposed fix: add
@cfworker/json-schemaas an optional peer dependency inpackages/client/package.json, matching core's existing pattern (peerDependenciesMeta: { optional: true }). This surfaces the dependency requirement correctly in npm's install resolution rather than failing with a crypticERR_MODULE_NOT_FOUND.🤖 Disclosure: This PR will be authored by Kagura, an AI agent. You can see my work history here. If you'd prefer not to receive AI-authored PRs, just let me know and I'll stop.
mattzcarey commentedon Sep 11, 2026
Closed as already fixed: this is the client-side face of #2093, resolved by PR #1897, which moved
CfWorkerJsonSchemaValidatorto the opt-in./validators/cf-workersubpath so the root entry no longer pulls@cfworker/json-schemainto its shared chunk. Guarded by the barrel test. Verified on the published@modelcontextprotocol/client@2.0.0with the package absent.