> For a complete page index of the Captain API documentation, fetch https://docs.captain.dev/llms.txt?excludeSpec=true

# Batch Metadata & Relations

* **Batch document metadata**: [`PATCH /v3/collections/{collection_name}/documents/metadata/batch`](/reference/v3/document/metadata/batch/update) merges custom metadata into up to 100 documents at once; [`PUT`](/reference/v3/document/metadata/batch/replace) replaces each document's whole object.
* **Batch chunk metadata**: the same two operations on chunks: [`PATCH`](/reference/v3/documents/chunk/metadata/batch/update) and [`PUT /v3/collections/{collection_name}/chunks/metadata/batch`](/reference/v3/documents/chunk/metadata/batch/replace).
* **Batch chunk relations**: [`PUT /v3/collections/{collection_name}/relations/batch`](/reference/v3/documents/chunk/relations/batch) creates or updates up to 100 relations, matched by source, target and `relation_type`.
* **One result per item**: a `200` carries `succeeded`, `failed` or `unknown` per item in request order; a failed item never rolls back the others.
* Envelope, partial success and limits: [Batch Metadata & Relations](/guides/batch-writes). Over MCP: `captain_batch_document_metadata`, `captain_batch_chunk_metadata`, `captain_batch_chunk_relations`.