# OpenCITE

> Verifiable scholarly evidence for AI agents. Verify references before citing them, search 250M+ open-access papers and heritage archives, and fetch any work by DOI/PMID/PMCID — every answer names its sources, flags retracted or corrected works, and says how complete the search was.

Base URL: https://citation.today · Contract: v3 (header `X-OpenCITE-API-Version: 3`) · OpenAPI: https://citation.today/openapi.json · Docs: https://citation.today/docs/

## What OpenCITE guarantees on every answer

1. Existence — each record resolves to a real work with a canonical id (DOI / PMID / PMCID / OpenAlex).
2. Provenance — each card names the upstream database (`source`) and the answer carries `meta.retrieved_at` + `meta.requestId`.
3. Completeness — `sources[]` lists which databases answered, failed or timed out; the coverage band prorates the charge, so you never pay for a blind answer.
4. Integrity flags — `evidence` on each card: retracted / corrected / expression of concern (with the notice DOI and date, from Crossref + Retraction Watch and OpenAlex), work type (preprint vs article), open-access status, DOAJ listing, licence. `evidence.status` is always explicit (`unknown` when it could not be checked).
5. Identifiable — every answer has a `meta.requestId`.

OpenCITE does NOT judge whether a paper's findings are true, and never labels journals "predatory". Only sourced facts.

## Tools / endpoints (API key required: `x-api-key: oc_live_…` or `Authorization: Bearer oc_live_…`)

- POST /api/verify — `{ "refs": ["10.1016/S0140-6736(97)11096-0", "Smith J. Title. Nature 2019;570:1-5."], "style": "apa" }` → per reference: `verdict` (verified | mismatch | not_found | ambiguous), `record`, `evidence`, corrected `citation`, `candidates`. Up to 50 refs; 0.1 credit each. USE THIS BEFORE OUTPUTTING ANY REFERENCE LIST.
- GET /api/search?q=…&limit=25&style=apa&detail=compact — deduplicated results across OpenAlex, Crossref, DOAJ, PubMed, Europeana, DPLA, Smithsonian, Internet Archive, Open Library and more. 1 credit per call, prorated by coverage.
- GET /api/works?id=<doi|pmid|pmcid|W-id>&include=cited-by|refs — one work, every identifier, evidence, optional citation graph. 0.1 credit (record) / 1 credit (with graph).
- GET /api/citations, GET /api/ids — the same graph and id-crosswalk operations as standalone calls.
- GET /api/credits — balance (free).

Cards are compact by default (title, ≤3 authors, year, venue, doi, url, type, citedBy, evidence, one formatted citation). `detail=full` adds abstract, keywords, all authors and every citation format. `style` = apa | mla | bibtex | ris | csl-json.

## Errors (JSON body always carries `code`)

- 401 `unauthorized` → `signup_url`, `pricing`
- 402 `subscription_required` (free account) → `subscribe_url`, `pricing`, `packs` · `insufficient_credits` → `balance`, `upgrade_url`, `packs` · `spend_cap_reached` → `manage_url` · `payment_failed` → `portal_url` · `trial_exhausted` → `resets_at` (a human must act on all of these)
- 429 `rate_limited` → `retry_after` seconds

## MCP

- npm: `npx -y opencite-mcp` (stdio). Tools: `verify_citations`, `search_papers`, `get_paper`. Env: `OPENCITE_API_KEY`.
- Claude Code: `claude mcp add opencite -e OPENCITE_API_KEY=oc_live_… -- npx -y opencite-mcp`
- Claude Desktop / any stdio client: `{ "mcpServers": { "opencite": { "command": "npx", "args": ["-y", "opencite-mcp"], "env": { "OPENCITE_API_KEY": "oc_live_…" } } } }`

## Keys and pricing

- Trial: `POST /api/verify` needs no key — 25 references per day per caller.
- Pay as you go: $2.50 per 1,000 calls (verify and id lookups $0.25 per 1,000), 1,000 calls a month included, $0 base fee, card at sign-up, invoiced monthly in arrears, user-set monthly cap (default $25). Prepaid packs at the same rate: $10 → 4,000 · $50 → 20,000 · $150 → 60,000 credits.
- 1 credit = one search or citation-graph call; verification, id lookup and a work fetched without a graph = 0.1 credit. Spending order: monthly allowance → purchased credits → metered usage.
- Sign in at https://citation.today → Developers → Create key. Plans: https://citation.today/#developers

## Licensing

Every response lists the metadata licence of each source present under `licenses` (e.g. OpenAlex, DOAJ, Europeana, DPLA, Smithsonian, Wikidata are CC0; Crossref metadata is usable for any purpose; PubMed/LoC are US public domain). Full table: https://citation.today/docs/licensing.html. Per-work content licences, where stated, are in `evidence.license`. Terms: https://citation.today/legal/terms.html · Privacy: https://citation.today/legal/privacy.html