About this tool
The defaults follow the Netflix English timed text style guide: up to 42 characters per line, at most 2 lines, a reading speed of up to 20 characters per second for adult content (17 for children’s content), a minimum duration of five-sixths of a second and a maximum of 7 seconds.
The checker also finds overlapping cues and subtitles that end before they start.
How subtitle files are built
SRT and VTT are plain text files, so you can open them in any text editor. Each subtitle is a block: a time range and one or two lines of text, followed by a blank line.
| SRT | VTT (WebVTT) | |
|---|---|---|
| First line of the file | The number 1 | The word WEBVTT |
| Cue numbers | Required, counting from 1 | Optional |
| Time format | 00:01:02,500 (comma before milliseconds) | 00:01:02.500 (full stop before milliseconds) |
| Styling and position | Basic tags in some players | Cue settings and CSS classes |
| Used by | Video editors, VLC, YouTube | HTML5 video players, web course platforms, YouTube |
Most conversion problems come from three things. Encoding: save subtitle files as UTF-8, or accented letters and non-Latin scripts turn into symbols. Separators: a full stop in an SRT timestamp, or a comma in a VTT one, makes many players skip the cue. Missing blank lines: every cue must be followed by an empty line, including the last one in some players. The tools on this site fix all three automatically.
Timing matters as much as the text. Professional guidelines keep each subtitle on screen between about five sixths of a second and seven seconds, at a reading speed of 17 to 20 characters per second for adults, with a short gap between cues so the eye notices the change. The subtitle checker flags cues that break these rules.
Everything you paste or open in these tools stays in your browser. Nothing is uploaded, so they are safe to use with unreleased or confidential material.
Need a transcript or subtitles from a recording? Transcribe audio or video free, then export SRT, VTT, Word or text.