MCP plugin on Cloudflare workers is not working

[promentol]

Describe the Bug

MCP plugin is not working on Cloudflare workers

After debugging locally the issue is following

[wrangler:info] POST /api/mcp 500 Internal Server Error (359ms)
✘ [ERROR] Uncaught Error: The Workers runtime canceled this request because it detected that your Worker's code had hung and would never generate a response. Refer to: https://developers.cloudflare.com/workers/observability/errors/ 

Theoretically, there is some action or unresolved promise, which needs to be wrapped inside ctx.waitUntil or just awaited

Link to the code that reproduces this issue

https://github.com/promentol/payload-mcp-cloudflare-demo

Reproduction Steps

Start Cloudflare worker template
Integrate MCP servier
MCP server works fine with next dev
After building and running with wrangler dev or when deploying to workers, it throws error when connecting to MCP server

Which area(s) are affected? (Select all that apply)

plugin: other

Environment Info

Node.js v24.1.0

Binaries:
  Node: 24.1.0
  npm: 11.3.0
  Yarn: N/A
  pnpm: 9.11.0
Relevant Packages:
  payload: 3.64.0
  next: 15.4.7
  @payloadcms/db-d1-sqlite: 3.64.0
  @payloadcms/drizzle: 3.64.0
  @payloadcms/graphql: 3.64.0
  @payloadcms/next/utilities: 3.64.0
  @payloadcms/plugin-cloud-storage: 3.64.0
  @payloadcms/plugin-mcp: 3.64.0
  @payloadcms/richtext-lexical: 3.64.0
  @payloadcms/storage-r2: 3.64.0
  @payloadcms/translations: 3.64.0
  @payloadcms/ui/shared: 3.64.0
  react: 19.1.0
  react-dom: 19.1.0
Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.4.0: Wed Feb 21 21:44:54 PST 2024; root:xnu-10063.101.15~2/RELEASE_ARM64_T6030
  Available memory (MB): 36864
  Available CPU cores: 12

[kendelljoseph]

Thank you for reporting this.

[promentol]

@kendelljoseph can you please provide guidance, I can try to fix and do Pull Request, where can be this potential issue?

[miantiao-me]

Running MCP on Cloudflare workers does indeed have some issues; in another project of mine this code works fine: https://github.com/TanStack/create-tsrouter-app/blob/main/frameworks/react-cra/add-ons/mcp/assets/src/utils/mcp-handler.ts

[kendelljoseph]

@promentol yep, I'm working on it. Thanks for your patience!

[kendelljoseph]

I was able to reproduce this @promentol.

I'm digging to see if its truly a lingering function, or something else.

[promentol]

@kendelljoseph we have this issue preventing release of production, can you give me guidance how to fix it, I will try to fix and make pull request

Thanks

[iofreddy85]

This is probably related to the same issue that occurs with Stripe API and Google Oauth APIs in the server. Anything that uses node:http or node:https modules inside cloudflare workers need some adjustments with the httpClients since those are not fully supported or have compatibility issues in the Isolated V8 environment used by CF workers.

Some rerences:
Stripe
Cloudflare

This is probably the place that would need some tweaking...
And this is how Stripe fixed the issue.

[kendelljoseph]

@promentol I'm debugging from cloudflare currently, I do see the error as well. @iofreddy85 thanks for the tip!

[promentol]

@kendelljoseph this error is preventing us to go to production with our app, can you please give me direction, I will try to fix it, there is more likely some promise which is not awaited IMHO