About headlint
headlint checks everything a web page's <head> declares: nine free checkers — meta tags, SERP snippet, social previews, favicons, head order, redirect chains, indexability, structured data and hreflang — plus a favicon generator whose output passes the checks by construction.
How it works
The checkers fetch your page the way each platform's crawler does (you can re-fetch with any platform's exact user agent), apply that platform's documented rules, and show which tag actually won. Where the markup makes claims about other resources, they get verified for real: icon files are downloaded and decoded, declared hreflang alternates are fetched and searched for return links, redirect chains are followed hop by hop, and robots.txt is evaluated with Google's own matching rules. Every spec-dependent rule shows the date it was last verified against the platform's own documentation. The favicon generator processes your file entirely in memory — the upload is never written to disk, never stored, and gone the moment your ZIP downloads.
Bot
Checks fetch your page as HeadlintBot/1.0 from this site's server. It requests one page plus a bounded set of the resources that page declares (its share image, icons and manifest, robots.txt, or declared hreflang alternates) per check, respects a strict size cap, and stores nothing but a 90-second in-memory cache.
Credits
Emoji favicons use Twemoji artwork (CC-BY 4.0). Text favicons and pixel measurements use the Liberation fonts (SIL OFL 1.1).