crossref-mcp-server

Tools

Seven tools for working with Crossref data — DOI resolution, full-text search across all scholarly works, outgoing reference lists, and journal, funder, and publisher lookup:

crossref_get_work

Resolve a DOI to its canonical Crossref record.

• DOI validated against 10.NNNN/suffix regex before the upstream call

• Returns title, authors with affiliations, abstract (when deposited), container/journal, publication date, work type, ISSN, license URLs, full-text link URLs, and funder acknowledgements

• Incoming citation count (is-referenced-by-count) is included; citing works are not — Crossref does not expose that data. Use OpenAlex for citation graphs.

crossref_search_works

Search across ~155M Crossref-registered works.

• Free-text query plus a structured filter object using Crossref's hyphen-separated key syntax: from-pub-date, until-pub-date, type, funder, issn, member, has-abstract, has-references, has-full-text, directory (use DOAJ to restrict to open-access content)

• Field-specific query parameters scope matching beyond the generic query: queryTitle, queryAuthor, queryContainerTitle (journal/book name), and queryBibliographic (whole-citation match to resolve a known reference to its DOI) — all combine with each other and with query

• Sort by relevance, is-referenced-by-count, published, deposited, or score

• fields parameter narrows response payload — useful for large result sets

• Offset paging up to ~10K results; deep paging requires cursor=* on the first call, then pass the returned nextCursor token. Cursor and offset cannot be combined.

crossref_get_references

Fetch the outgoing reference list for a DOI.

• Each reference includes its raw citation string and, where Crossref has resolved it, a DOI for follow-up lookup

• Coverage varies by publisher — pre-2000 literature and non-participating publishers may have no reference list

• Single-hop only; agents that need N-hop traversal chain calls explicitly

crossref_search_journals

Find journal records by ISSN or title.

• include_works: true triggers a second upstream call to fetch the journal's most recent works by publication date

• Returns journal title, publisher, ISSN-L, subject areas, and total DOI count

crossref_search_funders

Find funders in the Crossref Funder Registry.

• Accepts a name query or a direct funder DOI

• include_works: true retrieves funded works for the matched funder

• Returns funder name, DOI, country, and alternate names

crossref_get_member

Resolve a Crossref member ID to its publisher/organization record.

• Members are the organizations that register DOIs — this answers "what does this publisher publish, and how completely do they deposit metadata?"

• Returns primary name, alternate imprint names, owned DOI prefixes, DOI counts (total/current/backfile), a per-work-type breakdown, and per-category metadata deposit coverage (references, abstracts, ORCIDs, funders, licenses, and more) as current/backfile fractions

• Pair with crossref_get_prefix to resolve a DOI prefix to the member ID first

crossref_get_prefix

Resolve a DOI prefix to its owning publisher.

• Accepts the registrant prefix of a DOI (e.g. 10.1038, no /suffix)

• Returns the publisher name and numeric member ID — the ID chains directly into crossref_get_member for the full record

• The Crossref prefix record is thin by design (owner name and member link only); richer publisher data lives on the member record

Related MCP server: @cyanheads/openalex-mcp-server

Features

Built on @cyanheads/mcp-ts-core:

• Declarative tool definitions — single file per tool, framework handles registration and validation

• Unified error handling across all tools

• Pluggable auth (none, jwt, oauth)

• Swappable storage backends: in-memory, filesystem, Supabase, Cloudflare KV/R2/D1

• Structured logging with optional OpenTelemetry tracing

• STDIO and Streamable HTTP transports

Crossref-specific:

• Polite-pool User-Agent header injected on every request — priority access granted via CROSSREF_MAILTO email address, no API token required

• withRetry: 3 attempts, exponential backoff, handles both 429 and 503 responses

• Cursor-based deep paging for result sets beyond the ~10K offset cap

• Filter key validation: Crossref uses hyphens (has-abstract, has-references, from-pub-date); the server enforces correct syntax and surfaces API validation errors with actionable recovery hints

Getting started

Add the following to your MCP client configuration file. CROSSREF_MAILTO is optional but recommended — without it the server uses Crossref's anonymous pool with stricter rate limits.

{
  "mcpServers": {
    "crossref-mcp-server": {
      "type": "stdio",
      "command": "bunx",
      "args": ["@cyanheads/crossref-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info",
        "CROSSREF_MAILTO": "your-email@example.com"
      }
    }
  }
}

Or with npx (no Bun required):

{
  "mcpServers": {
    "crossref-mcp-server": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@cyanheads/crossref-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info",
        "CROSSREF_MAILTO": "your-email@example.com"
      }
    }
  }
}

Or with Docker:

{
  "mcpServers": {
    "crossref-mcp-server": {
      "type": "stdio",
      "command": "docker",
      "args": [
        "run", "-i", "--rm",
        "-e", "MCP_TRANSPORT_TYPE=stdio",
        "-e", "CROSSREF_MAILTO=your-email@example.com",
        "ghcr.io/cyanheads/crossref-mcp-server:latest"
      ]
    }
  }
}

For Streamable HTTP, set the transport and start the server:

MCP_TRANSPORT_TYPE=http MCP_HTTP_PORT=3010 CROSSREF_MAILTO=your-email@example.com bun run start:http
# Server listens at http://localhost:3010/mcp

Prerequisites

• Bun v1.3.14 or higher (or Node.js v24+).

• An email address for CROSSREF_MAILTO is optional but recommended — Crossref's polite pool grants priority access to clients that identify themselves. No account or token is required.

Installation

1. Clone the repository:

git clone https://github.com/cyanheads/crossref-mcp-server.git

2. Navigate into the directory:

cd crossref-mcp-server

3. Install dependencies:

bun install

4. Configure environment:

cp .env.example .env
# edit .env and optionally set CROSSREF_MAILTO for polite-pool access

Configuration

All configuration is validated at startup via Zod schemas in src/config/server-config.ts.

See .env.example for the full list of optional overrides.

Running the server

Local development

• Build and run:

  # One-time build
  bun run rebuild
  
  # Run the built server
  bun run start:stdio
  # or
  bun run start:http

• Run checks and tests:

  bun run devcheck   # Lint, format, typecheck, security
  bun run test       # Vitest test suite
  bun run lint:mcp   # Validate MCP definitions against spec

Project structure

Development guide

See CLAUDE.md for development guidelines and architectural rules. The short version:

• Handlers throw, framework catches — no try/catch in tool logic

• Use ctx.log for request-scoped logging, ctx.state for tenant-scoped storage

• Register new tools via the barrel in src/mcp-server/tools/definitions/index.ts

• Wrap external API calls: validate raw → normalize to domain type → return output schema; never fabricate missing fields (abstracts, reference lists, and affiliations are frequently absent in Crossref records)

Contributing

Issues and pull requests are welcome. Run checks and tests before submitting:

bun run devcheck
bun run test

License

Apache-2.0 — see LICENSE for details.