I have composio hooked in as an external MCP tool server in open-webui, and openrouter as my model provider. When I try use an Anthropic model and type in a chat that has the Composio tool enabled, I get an error message. Openrouter shows the following: { "type": "error", "error": { "type": "invalid_request_error", "message": "tools.32.custom.input_schema: input_schema does not support oneOf, allOf, or anyOf at the top level" }, "request_id": "req_vrtx_011CfPW6AgP8QoFa2FKtEYyH" } The same test without Composio enabled as a tool in open-webui works OK. From what I gather Anthropic models do not support oneOf/allOf/anyOf at the top level of the tool schemas - is there any way to fix this on the composio side of things?

Hi, Thanks for reporting the error and including OpenRouter's message. It means the model request contains a tool with

oneOf

,

allOf

, or

anyOf

at the top level of its input schema, which that Anthropic endpoint rejects. Your test with Composio disabled narrows the problem to the tool-enabled path, but the error does not identify whether tool 32 came from Composio or how Open WebUI passed its schema to OpenRouter. We can't yet confirm a Composio setting that makes this external MCP path generate strict-compatible schemas. The decisive comparison is tool 32 as sent to OpenRouter against the tool definition returned by Composio's MCP server. That will show whether a Composio schema change can address this case. You don't need to change your connection or scopes for this error.

The error does not occur when I disable only composio but leave all the other tools enabled. It is only the composio tool that causes this error. I will do some more digging to find the details of the tool 32 definition as you mentioned.

Thanks for the thorough digging — your curl output settles it.

COMPOSIO_MANAGE_SKILL

is one of the session meta tools our hosted MCP/Tool Router server exposes, and you're correct that its

inputSchema

currently has a top-level

anyOf

. Anthropic's tool-use API rejects `oneOf`/`allOf`/`anyOf` at the top level of a tool's

input_schema

, and Open WebUI passes MCP tool schemas through to OpenRouter unchanged — so any Anthropic model + the Composio MCP server fails at request validation, while other providers accept the schema as-is. To answer your question directly: there's no setting on your side today that makes the hosted MCP server emit Anthropic-strict schemas — this needs a fix on our side (flattening that tool's top-level

anyOf

, e.g. into an object with a discriminator field, the same way we already normalize schemas for provider-specific constraints elsewhere). I've filed this as a schema-compatibility bug against the Tool Router backend, referencing this thread. Workarounds until then: 1. Disable just that tool. If your Open WebUI setup lets you toggle individual tools from an MCP server, turn off only

COMPOSIO_MANAGE_SKILL

— it's the skill-management meta tool and isn't needed for normal tool discovery/execution (

COMPOSIO_SEARCH_TOOLS

,

COMPOSIO_MULTI_EXECUTE_TOOL

, etc. will still work). If Open WebUI only exposes the server as a single on/off tool, let me know and I'll check whether we can exclude it from your session config server-side. 2. Use a non-Anthropic model for chats that need Composio tools (as you've found).