Structure
Overlapping cues, backwards or zero-length timing, cues out of order, and cues with no text.
Subtitle validator
Check a subtitle file for errors.
Paste an SRT or VTT file and see every overlapping cue, backwards timestamp, overlong line, and caption that goes past a readable speed. The check runs in your browser and reports only.
Browser subtitle checker
Check a subtitle file before you ship it.
4cues
1errors
7warnings
Report
- Cue 2 at 00:00:02,500This cue starts 0.50s before cue 1 finishes, so two captions are on screen at once.
- Cue 2 at 00:00:02,500Line 1 is 49 characters, above the 42 character limit for this profile.
- Cue 2 at 00:00:02,500Reading speed is 32.7 characters per second, above the 20 this profile allows. Shorten the line or hold the cue longer.
- Cue 3 at 00:00:05,000The cue is on screen for 0.20s, below the 0.83s minimum for this profile.
- Cue 3 at 00:00:05,000Line 1 is 71 characters, above the 42 character limit for this profile.
- Cue 3 at 00:00:05,000Reading speed is 355.0 characters per second, above the 20 this profile allows. Shorten the line or hold the cue longer.
- Cue 4 at 00:00:20,000The cue is on screen for 11.0s, above the 7s maximum for this profile.
- Cue 4 at 00:00:20,000Line 1 is 47 characters, above the 42 character limit for this profile.
Fastest cue in this file reads at 355.0 characters per second. The Netflix, adult programs profile allows up to 20.
The check runs in your browser and reports only. It does not change the file. Warnings are style limits for the selected profile, not errors in the file itself.
The faults a player will not warn you about
A subtitle file can be badly broken and still load without complaint. Players are forgiving, so the problems show up in front of an audience rather than at export. Two cues overlapping puts two captions on screen at once. A cue that ends before it starts either vanishes or hangs, depending on the player. A caption that flashes for two tenths of a second is technically present and practically unreadable.
Reading speed is the fault people notice without being able to name it. If a line is long and the cue is short, viewers feel rushed and stop reading. Netflix puts a number on this in its Timed Text Style Guide: up to 20 characters per second for adult programs, up to 17 for children's programs, with 42 characters per line, a minimum of five sixths of a second per subtitle event and a maximum of seven seconds.
Those numbers were written for long-form streaming, and they are a reasonable default for most video. For vertical short-form the line length matters more than the specification suggests, because a phone frame gives captions a much narrower safe area than a widescreen one.
What the validator checks
Readability
Characters per second per cue, line length, and how many lines a single cue uses.
Duration
Cues held too briefly to read, and cues left on screen longer than the profile allows.
Fixing what the report finds
The validator reads SRT and WebVTT. If what you have is a styled ASS or SSA file, or an SBV file from YouTube Studio, convert it first and check the result.
If every cue is off by the same amount, or the file slides further out the longer it plays, that is a whole-file timing fault rather than a set of individual mistakes. Correct it with the subtitle timing shifter and read the guide to out-of-sync subtitles to tell the two apart.
Line lengths here are counted in grapheme clusters, the units a reader perceives, rather than in code units. For English the two are the same number. For Devanagari, Kannada and the other Indic scripts they are not, and a naive count reports those lines at close to double their real length. The guide to subtitle character limits explains what that fixes and, just as usefully, what it does not: no character count measures width or height, so Nastaliq and vertically stacked scripts still need a look in the player.
Reading speed and line length warnings are wording problems, not timing problems. The fix is to shorten the line or split the cue, which is work best done where the caption text is still editable. Start from the video in the AutoCaption caption generator, and use the caption line break guide for where to split. If you need the file in another format afterwards, the SRT to VTT converter handles that.
Subtitle validation questions
What does this subtitle validator check?
Overlapping cues, cues that end before they start, cues out of order, cues with timing but no text, cues held too briefly or too long, lines above the character limit, more lines than the profile allows, and reading speed in characters per second.
What reading speed should subtitles use?
Netflix publishes up to 20 characters per second for adult programs and up to 17 for children's programs in its Timed Text Style Guide, alongside 42 characters per line. Those are the numbers the Netflix profiles here check against.
Is a warning the same as a broken file?
No. Errors mean the file is structurally wrong, such as a cue that ends before it starts or two captions on screen at once. Warnings mean the file breaks a style limit for the profile you picked, which may be fine depending on where the video is going.
Why does the short-form profile use shorter lines?
Vertical video gives captions a much narrower safe area than a widescreen frame, so a line that fits comfortably on a television runs past the edge on a phone. That profile is a practical working limit rather than a published external standard.
Does this tool change my subtitle file?
No. The validator reports and nothing else. It runs in your browser, reads the file locally, and leaves the file exactly as it was.
How do I fix the problems it finds?
Timing faults that affect the whole file are usually an offset or a frame-rate mismatch, which the subtitle timing shifter handles. Wording, line breaks, and cue boundaries are best corrected where the caption text is still editable, in the AutoCaption caption generator. Open the caption generator.
Captions that need rewriting, not checking?
Generate the track from the video, fix the wording and the cue boundaries, then export SRT, VTT, text, or a captioned video.