Citations

Claude can provide detailed citations when answering questions about documents, helping you track and verify the sources behind each response.

All active models support citations.

The following example shows how to enable citations on a plain text document with the Messages API:

client = anthropic.Anthropic()

response = client.messages.create(
    model="claude-opus-5",
    max_tokens=1024,
    messages=[
        {
            "role": "user",
            "content": [
                {
                    "type": "document",
                    "source": {
                        "type": "text",
                        "media_type": "text/plain",
                        "data": "The grass is green. The sky is blue.",
                    },
                    "title": "My Document",
                    "context": "This is a trustworthy document.",
                    "citations": {"enabled": True},
                },
                {"type": "text", "text": "What color is the grass and sky?"},
            ],
        }
    ],
)
print(response)

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How citations work

Integrate citations with Claude in these steps:

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Citable versus non-citable content

• Text found within a document's source content can be cited from.
• title and context are optional fields that are passed to the model but not used toward cited content.
• title is limited in length, so the context field is useful for storing document metadata as text or stringified JSON.

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Citation indices

• Document indices are 0-indexed from the list of all document content blocks in the request (spanning across all messages).
• Character indices are 0-indexed with exclusive end indices.
• Page numbers are 1-indexed with exclusive end page numbers.
• Content block indices are 0-indexed with exclusive end indices from the content list provided in the custom content document.

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Token costs

• Enabling citations incurs a slight increase in input tokens because of system prompt additions and document chunking.
• However, the citations feature is very efficient with output tokens. Internally, the model outputs citations in a standardized format that are then parsed into cited text and document location indices. The cited_text field is provided for convenience and does not count toward output tokens.
• When passed back in subsequent conversation turns, cited_text is also not counted toward input tokens.

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Feature compatibility

Citations work in conjunction with other API features including prompt caching, token counting, and batch processing.

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Using prompt caching with citations

Citations and prompt caching can be used together effectively.

The citation blocks generated in responses cannot be cached directly, but the source documents they reference can be cached. To optimize performance, apply cache_control to your top-level document content blocks.

client = anthropic.Anthropic()

# Long document content (for example, technical documentation)
long_document = (
    "This is a very long document with thousands of words..." + " ... " * 1000
)  # Minimum cacheable length

response = client.messages.create(
    model="claude-opus-5",
    max_tokens=1024,
    messages=[
        {
            "role": "user",
            "content": [
                {
                    "type": "document",
                    "source": {
                        "type": "text",
                        "media_type": "text/plain",
                        "data": long_document,
                    },
                    "citations": {"enabled": True},
                    "cache_control": {
                        "type": "ephemeral"
                    },  # Cache the document content
                },
                {
                    "type": "text",
                    "text": "What does this document say about API features?",
                },
            ],
        }
    ],
)
print(response)

In this example:

• The document content is cached using cache_control on the document block.
• Citations are enabled on the document.
• Claude can generate responses with citations while benefiting from cached document content.
• Subsequent requests using the same document benefit from the cached content.

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Document types

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Choosing a document type

Three document types are supported for citations. Documents can be provided directly in the message (base64, text, or URL) or uploaded through the Files API and referenced by file_id:

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Plain text documents

Plain text documents are automatically chunked into sentences. You can provide them inline or by reference with their file_id:

{
  "type": "document",
  "source": {
    "type": "text",
    "media_type": "text/plain",
    "data": "Plain text content..."
  },
  "title": "Document Title",
  "context": "Context about the document that will not be cited from",
  "citations": { "enabled": true }
}

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PDF documents

PDF documents can be provided as base64-encoded data, a URL, or by file_id. PDF text is extracted and chunked into sentences. As image citations are not yet supported, PDFs that are scans of documents and do not contain extractable text are not citable.

client = anthropic.Anthropic()

pdf_base64 = base64.standard_b64encode(
    pathlib.Path("/path/to/document.pdf").read_bytes()
).decode()

response = client.messages.create(
    model="claude-opus-5",
    max_tokens=1024,
    messages=[
        {
            "role": "user",
            "content": [
                {
                    "type": "document",
                    "source": {
                        "type": "base64",
                        "media_type": "application/pdf",
                        "data": pdf_base64,
                    },
                    "title": "Document Title",
                    "context": "Context about the document that will not be cited from",
                    "citations": {"enabled": True},
                },
                {"type": "text", "text": "Summarize this document."},
            ],
        }
    ],
)
print(response)

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Custom content documents

Custom content documents give you control over citation granularity. No additional chunking is done and chunks are provided to the model according to the content blocks provided.

client = anthropic.Anthropic()

response = client.messages.create(
    model="claude-opus-5",
    max_tokens=1024,
    messages=[
        {
            "role": "user",
            "content": [
                {
                    "type": "document",
                    "source": {
                        "type": "content",
                        "content": [
                            {"type": "text", "text": "First chunk"},
                            {"type": "text", "text": "Second chunk"},
                        ],
                    },
                    "title": "Document Title",
                    "context": "Context about the document that will not be cited from",
                    "citations": {"enabled": True},
                },
                {"type": "text", "text": "Summarize this document."},
            ],
        }
    ],
)
print(response)

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Response structure

When citations are enabled, responses include multiple text blocks with citations:

{
  "content": [
    { "type": "text", "text": "According to the document, " },
    {
      "type": "text",
      "text": "the grass is green",
      "citations": [
        {
          "type": "char_location",
          "cited_text": "The grass is green.",
          "document_index": 0,
          "document_title": "Example Document",
          "start_char_index": 0,
          "end_char_index": 20
        }
      ]
    },
    { "type": "text", "text": " and " },
    {
      "type": "text",
      "text": "the sky is blue",
      "citations": [
        {
          "type": "char_location",
          "cited_text": "The sky is blue.",
          "document_index": 0,
          "document_title": "Example Document",
          "start_char_index": 20,
          "end_char_index": 36
        }
      ]
    },
    {
      "type": "text",
      "text": ". Information from page 5 states that "
    },
    {
      "type": "text",
      "text": "water is essential",
      "citations": [
        {
          "type": "page_location",
          "cited_text": "Water is essential for life.",
          "document_index": 1,
          "document_title": "PDF Document",
          "start_page_number": 5,
          "end_page_number": 6
        }
      ]
    },
    {
      "type": "text",
      "text": ". The custom document mentions "
    },
    {
      "type": "text",
      "text": "important findings",
      "citations": [
        {
          "type": "content_block_location",
          "cited_text": "These are important findings.",
          "document_index": 2,
          "document_title": "Custom Content Document",
          "start_block_index": 0,
          "end_block_index": 1
        }
      ]
    }
  ]
}

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Streaming support

For streaming responses, citations arrive as a citations_delta delta type inside content_block_delta events. Each delta contains a single citation to add to the citations list on the current text content block.

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Next steps