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Subtitle utility

WebVTT Validator Online

Validate WebVTT captions online and check missing WEBVTT headers, timestamp syntax, cue order, and HTML5 caption issues.

Free No signup Browser-local

VTT input

No signup. No server upload. Browser-only processing.

Drop a subtitle file here or choose one manually

Supports SRT, VTT, and ASS where relevant to the tool.

Selected file: sample.vtt

Validation report

Runs locally in your browser

Selected file: sample.vtt

Workflow notes

How to use this VTT validator tool

Use this before publishing captions with HTML5 video when VTT captions do not load or a player rejects the file. The validator checks for a missing WEBVTT header, parseable cues, dot-based timestamps, cue order, and common browser caption issues locally with no upload.

  1. Add a supported subtitle file. Upload or paste a supported subtitle file (.vtt, .txt), or load the sample input to see the expected structure.
  2. Run the VTT validator tool. Use the browser-based converter or repair action to process the subtitle file locally on your device.
  3. Review and download the output. Check the first few cues, the middle of the file, and the final cue before copying or downloading the result.

Input and output checklist

  • Use a complete subtitle file with valid cue timing when possible.
  • Keep a copy of the original file before replacing it in your workflow.
  • Review the first few cues, the middle of the file, and the final cue after export.
  • Test the downloaded output in the destination player, editor, or upload form.

Common mistakes to avoid

  • Publishing a VTT file without the WEBVTT header.
  • Using comma-based SRT timestamps in a WebVTT file.
  • Ignoring player-side problems such as CORS, MIME type, or an unreachable VTT URL after validation passes.

All processing runs in your browser, so the subtitle or video file does not need to be uploaded to a server. That is useful for client review files, unreleased videos, internal training material, and other caption workflows where the text should stay on your device.

When to use this tool

Use this free WebVTT validator when captions do not load in HTML5 video or a browser player rejects a VTT file. Check the header, timestamps, cue order, and parseable cues locally.

  • Check WebVTT files before using them in HTML5 video.
  • Find missing WEBVTT headers that stop captions from loading.
  • Detect comma-based SRT timestamps inside VTT files.
  • Diagnose VTT captions that do not render in a browser player.

FAQ

Is this WebVTT validator free? +

Yes. You can validate WebVTT captions for free in your browser without signup or upload.

Does the validator repair VTT files? +

No. It outputs a validation report. Use the SRT to VTT converter or edit the file if repairs are needed.

Can this help when VTT captions are not showing? +

Yes. The report checks file-level blockers such as a missing WEBVTT header, invalid timestamps, cue order problems, and parse errors before you debug the player setup.

Can it detect a missing WEBVTT header? +

Yes. The report flags VTT files that do not start with the WEBVTT header.

Does it count parsed cues? +

Yes. The report includes how many WebVTT cues were detected.

Are my VTT files uploaded to a server? +

No. Validation runs locally in your browser, so your caption file stays on your device.