Citations

Claude is capable of providing detailed citations when answering questions about documents, helping you track and verify information sources in responses.

All active models support citations, with the exception of Haiku 3.

Citations with Claude Sonnet 3.7

Claude Sonnet 3.7 may be less likely to make citations compared to other Claude models without more explicit instructions from the user. When using citations with Claude Sonnet 3.7, we recommend including additional instructions in the user turn, like "Use citations to back up your answer." for example.

We've also observed that when the model is asked to structure its response, it is unlikely to use citations unless explicitly told to use citations within that format. For example, if the model is asked to use <result> tags in its response, you should add something like "Always use citations in your answer, even within <result> tags."

Please share your feedback and suggestions about the citations feature using this form.

Here's an example of how to use citations with the Messages API:

curl https://api.anthropic.com/v1/messages \
  -H "content-type: application/json" \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "claude-sonnet-4-5",
    "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?"
          }
        ]
      }
    ]
  }'

Comparison with prompt-based approaches

In comparison with prompt-based citations solutions, the citations feature has the following advantages:

Cost savings: If your prompt-based approach asks Claude to output direct quotes, you may see cost savings due to the fact that cited_text does not count towards your output tokens.
Better citation reliability: Because we parse citations into the respective response formats mentioned above and extract cited_text, citations are guaranteed to contain valid pointers to the provided documents.
Improved citation quality: In our evals, we found the citations feature to be significantly more likely to cite the most relevant quotes from documents as compared to purely prompt-based approaches.

How citations work

Integrate citations with Claude in these steps:

Automatic chunking vs custom content

By default, plain text and PDF documents are automatically chunked into sentences. If you need more control over citation granularity (e.g., for bullet points or transcripts), use custom content documents instead. See Document Types for more details.

For example, if you want Claude to be able to cite specific sentences from your RAG chunks, you should put each RAG chunk into a plain text document. Otherwise, if you do not want any further chunking to be done, or if you want to customize any additional chunking, you can put RAG chunks into custom content document(s).

Citable vs non-citable content

Text found within a document's source content can be cited from.
title and context are optional fields that will be passed to the model but not used towards cited content.
title is limited in length so you may find the context field to be useful in storing any document metadata as text or stringified json.

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.

Token costs

Enabling citations incurs a slight increase in input tokens due to system prompt additions and document chunking.
However, the citations feature is very efficient with output tokens. Under the hood, the model is outputting 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 towards output tokens.
When passed back in subsequent conversation turns, cited_text is also not counted towards input tokens.

Feature compatibility

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

Citations and Structured Outputs are incompatible

Citations cannot be used together with Structured Outputs. If you enable citations on any user-provided document (Document blocks or RequestSearchResultBlock) and also include the output_format parameter, the API will return a 400 error.

This is because citations require interleaving citation blocks with text output, which is incompatible with the strict JSON schema constraints of structured outputs.

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.

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 will benefit from the cached content

Document Types

Choosing a document type

We support three document types for citations. Documents can be provided directly in the message (base64, text, or URL) or uploaded via the Files API and referenced by file_id:

Type	Best for	Chunking	Citation format
Plain text	Simple text documents, prose	Sentence	Character indices (0-indexed)
PDF	PDF files with text content	Sentence	Page numbers (1-indexed)
Custom content	Lists, transcripts, special formatting, more granular citations	No additional chunking	Block indices (0-indexed)

.csv, .xlsx, .docx, .md, and .txt files are not supported as document blocks. Convert these to plain text and include directly in message content. See Working with other file formats.

Plain text documents

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

PDF documents

PDF documents can be provided as base64-encoded data 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 will not be citable.

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.

{
    "type": "document",
    "source": {
        "type": "content",
        "content": [
            {"type": "text", "text": "First chunk"},
            {"type": "text", "text": "Second chunk"}
        ]
    },
    "title": "Document Title", # optional
    "context": "Context about the document that will not be cited from", # optional
    "citations": {"enabled": True}
}

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
            }]
        }
    ]
}

Streaming Support

For streaming responses, we've added a citations_delta type that contains a single citation to be added to the citations list on the current text content block.

import anthropic

client = anthropic.Anthropic()

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

response = client.messages.create(
    model="claude-sonnet-4-5",
    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?"
                }
            ]
        }
    ]
)

How citations work

Citable vs non-citable content

Citation indices

Token costs

Feature compatibility

Using Prompt Caching with Citations

Document Types

Choosing a document type

Plain text documents

Example plain text citation

PDF documents

Example PDF citation

Custom content documents

Example citation

Response Structure

Streaming Support

Example streaming events