VTT Validator
Check a WebVTT .vtt caption file for missing headers, timestamp errors, overlaps, empty cues and line-length problems. Runs entirely in your browser.
Local processing only. Your WebVTT file is validated on your device. Nothing is uploaded.
Input WebVTT
What this validator checks
- Presence of the
WEBVTTheader on the first line. - Parse errors on any cue timestamp line.
- End time after start time and no negative timestamps.
- Overlapping cues (more than 10ms of overlap).
- Very short (<500ms) and very long (>10s) durations.
- Empty dialogue in cues.
- Line-length advisories above 42 characters.
Severity levels
Errors mean the file is likely broken for at least some players. Warnings are worth reviewing. Info items are readability tips.
Supported input formats
WebVTT with WEBVTT header. Both HH:MM:SS.mmm and MM:SS.mmm timestamp styles are supported.
Limitations
- Full IEC 14496-30 compliance is not checked.
- Style, region and note blocks are skipped but not validated for syntax.
- Cue settings (position, line, align) are not validated.