Chroma MCP: Embedding function name mismatch (delete and re-index the collection)

TL;DR: You changed CHROMA_EMBEDDING_FUNCTION after the collection was created, and ChromaDB refuses to mix embedding functions. Delete the collection and re-index with the current setting. There is no in-place conversion.

Embedding function name mismatch

Fix it

1. Confirm the mismatch: the collection was created under one embedding function (e.g. default) and the server now configures another (e.g. openai or accurate).
2. Delete the affected collection. Use the MCP server's delete-collection tool or the API. This destroys the indexed data, so be sure you can re-index.
3. Re-index with the current embedding function. The server recreates the collection with the configured function on next use.

4. Restart the MCP client.

   Expected: the mismatch error is gone; queries use the new embedding function.

When to use this

• The error is exactly Embedding function name mismatch.
• You recently changed CHROMA_EMBEDDING_FUNCTION or the --embedding-function flag.

When NOT to use this

• The collection was created with the current setting and still fails. Then it is a different problem (check API keys for hosted embedding functions).
• Connection errors. Fix reachability first.

Compatibility

• chromamcpserver (djm81) and chroma-mcp servers with configurable embedding functions.

Why it happens

A collection's embedding function is fixed at creation because the stored vectors were produced by it. Query-time vectors must come from the same function or similarity is meaningless. ChromaDB enforces this rather than silently returning garbage.

Edge cases

• API-based embedding functions (OpenAI, Cohere, Gemini) need their API keys set (CHROMA_OPENAI_API_KEY style vars) or creation fails differently.
• If several collections exist, each must be rebuilt. Audit all of them after a function change.
• Decide on the embedding function once per project and stop changing it. Re-indexing is the tax on indecision.