Crossref

Crossref is a registry that links scholarly content with persistent DOI identifiers. When a publisher registers a paper, Crossref assigns it a DOI — a permanent link that never breaks — and stores its metadata: title, authors, journal, and references. It is the infrastructure behind academic citations, used by publishers, libraries, and researchers worldwide.

Key Features

Free DOI lookup for any scholarly work
Metadata for millions of papers, books, and datasets
Citation linking between works
Free API for developers and publishers
Reference checking and validation
No account needed

Pricing

Plan	Price	Details
Free	$0	DOI lookup, metadata, and API access — no payment required.

Prices as listed in 2026 research. Always check the official site for the latest price — plans change. Free plan: Yes — it has a free plan.

Best for: anyone who needs to find, link, or cite a paper by its DOI.
Popular with: Students, Teachers, Developers

How it works

The service is free for anyone to search, with no account needed. You can look up any DOI to find a paper's metadata, resolve a citation, or check whether a reference is correct. It also offers a free API for developers who build citation tools.

Crossref is not a search engine or a reading tool — it is the registry that makes citations work. For anyone who needs to find a paper by its DOI, verify a reference, or build a tool that uses citation data, it is the authoritative source.

Pros and Cons

✓ Pros

Authoritative source for DOI and citation data
Completely free with no account needed
Free API for building citation tools
Used by publishers worldwide

✗ Cons

A registry, not a search engine — no full-text search
Interface is built for publishers and developers
No AI features or reading tools

Key Features

Pricing

How it works

Pros and Cons

✓ Pros

✗ Cons

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Perplexity

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