Answer with citations that point at the source text

Approach

Send documents as document content blocks with "citations": {"enabled": True}. Text blocks in the response then carry citations with the cited_text and its location, which you can render as footnotes. Citations must be enabled on all documents in a request or none.

Solution

import anthropic

client = anthropic.Anthropic()


def doc_block(title: str, text: str) -> dict:
    return {"type": "document", "title": title, "citations": {"enabled": True},
            "source": {"type": "text", "media_type": "text/plain", "data": text}}


def cited_answer(question: str, documents: dict[str, str]) -> str:
    response = client.messages.create(
        model="claude-sonnet-5-5",
        max_tokens=1024,
        messages=[{"role": "user", "content": [*(doc_block(t, body) for t, body in documents.items()),
                                                 {"type": "text", "text": question}]}],
    )
    parts, notes = [], []
    for block in response.content:
        if block.type != "text":
            continue
        parts.append(block.text)
        for c in block.citations or []:
            notes.append(f'[{len(notes) + 1}] {c.document_title}: "{c.cited_text.strip()}"')
            parts.append(f"[{len(notes)}]")
    return "".join(parts) + "\n\n" + "\n".join(notes)


print(cited_answer("What is the refund window?",
                   {"Refund policy": "Refunds are available within 30 days of purchase. Gift cards are excluded."}))

Pitfalls

• Enabling citations on some documents but not others in the same request.
• Showing citations without the document title or link, so users can't check them.
• Assuming a cited sentence means the whole answer is supported; review uncited text too.

Variations

• PDF documents ("source": {"type": "base64", "media_type": "application/pdf", ...}) return page locations.
• Use custom content documents to control the citation granularity (for example one block per paragraph).

Further reading: Citations