MCP quit connecting to Claude on Mac

Help & Support
1

Hola, good morning,

first of all, congrats on the work. Really useful add on!

I’ve been using it succesfully for a few months, but now Claude has lost connection. It says possibly due to some update from the MCP. I’ll paste Claude’s message here.

Subject: All tools fail validation on MCP clients that validate outputSchema (draft-07 vs 2020-12)

Hi,

I’m using the Anki MCP Server through Claude (Cowork / desktop app, tools proxied
to a remote session). The server connects fine and the full tool list is exposed
to the model, but every tool call fails before it ever reaches AnkiConnect,
with this client-side error:

Error: Tool ‘listDecks’ has an invalid outputSchema: JSON Schema declares an
unsupported dialect (“$schema”: “http://json-schema.org/draft-07/schema#”).
The default validator supports JSON Schema 2020-12 only; pass a pre-configured
Ajv instance to Ajv…

I get the identical error on listDecks, collection_stats, modelNames and getTags,
so it looks like it affects every tool that declares an outputSchema, not one
specific handler.

What seems to be happening: the tools’ outputSchema objects carry
“$schema”: “http://json-schema.org/draft-07/schema#”. The client validates
structured tool output with Ajv in its 2020-12-only configuration, so it rejects
the schema at registration/call time and the request is never dispatched. Nothing
is wrong with AnkiConnect or the local Anki install — the failure is purely in
schema validation on the client side, and there’s no setting I can change from
my end to work around it.

This looks like the classic zod-to-json-schema default: it emits draft-07 unless
told otherwise. Two possible fixes on your side:

  1. Simply omit the “$schema” key from the generated outputSchema objects. Most
    clients then validate with their own default dialect and it works. This is
    usually a one-line change (e.g. delete schema.$schema after generation).
  2. Emit 2020-12 explicitly — with zod-to-json-schema use
    target: "jsonSchema2020-12", or with Zod 4’s built-in
    z.toJSONSchema(schema, { target: "draft-2020-12" }) — and make sure no
    draft-07-only keywords survive the conversion.

Option 1 is probably the safest for broad client compatibility, since the MCP
spec doesn’t pin a dialect and different hosts validate differently.

Happy to test a patched build and report back if that helps.

Thanks for the work on this server.

Thank’s a lot

2

Thank you. It’s really inspiring to hear that it’s useful.

Yes, it’s a known bug and it’s
already fixed. You should upgrade to the latest version to make it work again.

Let me know if it helped you.

3

Hi,

I am in a similar situation. I run Claude Dekstop and specifically use Claude Cowork 99% of the time. I have the latest versions of Claude Desktop, Anki, and AnkiMCP.

I am on the free tier and I run AnkiMCP locally on my Windows laptop. The connector works if I ask Claude to list my Anki decks on Claude Chat but on Claude Cowork, this is the response I get when I asked Claude why the connector works in Chat but not in Cowork:

The Anki MCP Server itself is fine. The failure happens in how this Cowork session validates its tool definitions.

  • What the error says: the server declares its output format using the JSON Schema “draft-07” dialect. The validator in this session accepts only the newer 2020-12 dialect, so it rejects the tool before the call reaches Anki. Nothing ever gets to Anki.
  • What I just tested: listDecks and collection_stats both fail with the same error. Earlier I said every tool on that server has the problem. I hadn’t tested that, but the second failure supports it, because the error is about the schema each tool declares.
  • Why Claude chat works: it calls the same server, but its client evidently doesn’t apply that strict check. That is my inference. I can’t see how chat’s client is built.
  • Why the fallback failed here: in chat, the cloud AnkiMCP hit its quota and the local server picked up the request. In this session the local server is the one being blocked, so nothing is left to fall back to.

This matches your notes: the connector was down for this same draft-07 error (GitHub issue #86142), then worked on 16 Aug 2026. The Cowork session validator is what has changed, or regressed.

  • Fix that works now: use Claude chat for Anki work, as you just did.
  • Fix in Cowork: the server needs to drop the $schema line from its tool output schemas, or Cowork needs to accept draft-07. Neither is something I can change from here.
  • Workaround in this session: I can screenshot Anki’s deck browser on your laptop. It needs your approval for computer access and Anki has to be open. It would give a card-count view but won’t match the structured list you got in chat. Say the word and I’ll do it.

I have no coding background and I am lost on how to fix this. It would be really great if I could continue to use Claude Cowork for my Anki needs.

Thanks in advance.

4

Hi,

Thanks for the detailed report. It made this easy to track down.

What’s happening: the draft-07 error was a real bug in our server, fixed in version 0.24.0 (mid-August). I just re-tested the current release (0.26.0) against Claude Desktop’s strict validator and every tool passes. So your Cowork session is almost certainly still reaching an older copy of the server. It works in Chat only because Chat doesn’t perform that check, while Cowork does.

One thing that trips people up: Cowork sessions load their list of local servers when the session starts. If you update the server, sessions you already had open keep using the old one, which can make a successful update look like it didn’t work.

To fix it:

  1. In Claude Desktop, open Settings → Extensions. If you see Anki MCP Server there, note the version number, then remove it.
  2. Download the latest .mcpb file from Release v0.26.0 · ankimcp/anki-mcp-server · GitHub and double-click it to install.
  3. Fully quit Claude Desktop: right-click the icon in the Windows system tray and choose Quit (closing the window isn’t enough), then reopen it.
  4. Start a brand-new Cowork session and ask it to list your Anki decks.

If you don’t see it under Extensions, it was set up through a config file instead. In that case, go to Settings → Developer → Edit Config, copy the contents, and send them to me. I’ll tell you exactly what to change.

If it still fails after that, reply with the version number from step 1 and the exact error text, and I’ll reopen the issue. For reference, the earlier report of the same error is here: Tools rejected by Claude MCP validator: outputSchema uses JSON Schema draft-07, Claude requires 2020-12 · Issue #67 · ankimcp/anki-mcp-server · GitHub

Best,
Anatoly