Developer Tools

HTML Validity Checker

Run local structural HTML checks for duplicate IDs, labels, links, headings, and document basics.

Built for developers, students, agencies, and QA teams who want a fast pre-validation pass.

Features

Built for quick checks.

Local quick checks

Checks duplicate IDs, empty href/src attributes, missing html lang, missing title, heading jumps, form labels, and image alt text.

Selectors and snippets

Findings include selector hints and short snippets where available so issues are easier to locate.

Honest scope

Positioned as a local quick check, not a replacement for formal W3C validation.

Privacy summary

Checks run locally in the active tab after user action. The current build does not send page HTML, findings, browsing history, or settings to A1 Local.

Permissions

activeTab
scripting
storage

Supporter roadmap

Saved reports
Batch URL checks
Client-ready exports