Subtitle Preflight Validator
Inspect SRT and WebVTT subtitle files for syntax errors, out-of-order cues, illegal overlaps, and reading speed spikes before you publish.
100% In-Browser · Zero Upload
Drop your subtitle file to validate
Supports .srt and .vtt files up to 25 MB
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Why Subtitle Validation is Critical Before Publishing
Whether you create YouTube videos, localized courses, or client edits, broken subtitle files can ruin viewer engagement or cause distribution platforms to reject your upload.
Top Subtitle Errors Detected by SubPreflight
- Timestamp Formatting Errors: Using dots instead of commas in SRT files (e.g.
00:01:23.456instead of00:01:23,456) breaks many desktop and broadcast video players. - Subtitles Displayed Too Briefly: When a caption flashes on screen for less than 1 second, viewers struggle to comprehend dialogue.
- Reading Speed Violations (High CPS): Captions with more than 21-25 characters per second require superhuman reading speed.
- Overlapping Cues: When cue A starts before cue B finishes, video players can flicker, skip dialogue, or corrupt closed captions.
Frequently Asked Questions
Are my video captions uploaded to your server?
No. All parsing, linting and repairs take place locally in your web browser using HTML5 File APIs and Web Workers. No file data is ever transmitted.
What is the difference between a Warning and an Error?
An Error indicates syntax that will cause players to fail, for example malformed timecodes or a negative duration. A Warning means the file works technically, but viewers will suffer from high reading speed or overlapping text.