ClientSideTools Privacy-First Browser Tools

Citation & Hallucination URL Checker

AI models frequently invent plausible-looking URLs, DOIs, and ISBNs. This tool extracts every citation from your text, validates its structure locally, and (optionally) checks live availability — so hallucinated references never reach your readers.

AI Workflows & Technical Writing Local structural checks Your text stays in your browser. Live checks only contact public lookup APIs you trigger.

Tool interface

Live checks are optional. They send only the extracted DOI/ISBN/URL (not your full text) to public lookup services (Crossref, OpenLibrary) or test host reachability.

Introduction

Large language models generate citations that look correct but do not exist — fabricated DOIs, dead URLs, and ISBNs with invalid checksums. This tool gives researchers, journalists, and technical writers a fast pre-publication screen.

How it works

  • Regex extraction finds URLs, DOIs (including doi.org links), and ISBNs.
  • Each citation is validated structurally, entirely in your browser.
  • If you choose, live checks query CORS-enabled public APIs (Crossref, OpenLibrary) or test whether a host responds.
  • Results are color-coded with text labels so they remain clear without color vision.

Reading the results

  • Valid: the citation is well-formed (and, if checked, resolvable).
  • Warning: well-formed but unverifiable locally (e.g., localhost, trailing punctuation).
  • Invalid: malformed structure or failed checksum — treat as likely hallucination.

Privacy & network behavior

Structural validation never leaves your browser. Live checks are opt-in and transmit only the individual citation string — never your full document. DOI checks use the Crossref REST API; ISBN checks use OpenLibrary; URL checks perform a no-cors reachability probe that reveals only that a host responded.

Limitations

  • CORS or network policies may mark legitimate sites as "unverifiable".
  • Reachability ≠ correctness: a live page can still be the wrong source.
  • Very new DOIs may not yet be indexed by Crossref.

FAQ

Does a green URL mean the source is trustworthy?

No. It means the URL is well-formed (and possibly reachable). It does not verify the page's content or that it supports your claim.

Why did my ISBN fail?

ISBNs include a checksum digit. Hallucinated ISBNs almost always fail it — a strong hallucination signal.

Is my document uploaded anywhere?

No. Only extracted citation strings are sent during optional live checks.

Related tools

References

Version and changelog

  • Version: 1.0.0
  • Last updated: August 12, 2026
  • Changelog: Initial production release.