SRT Validator
Find out why a subtitle file is rejected by a player or a video platform. The validator checks the structure of SRT and WebVTT files – cue numbers, timestamp syntax, the comma or dot before milliseconds – then the timing – cues that end before they start, overlap or are out of order – and finally readability: lines that are too long, cues with too many lines and text shown too briefly to be read. Each finding comes with its line number.
- Runs in your browser
- No sign-up
- Free to use
How to use SRT Validator
- Paste subtitles or open an .srt or .vtt file.
- Choose the line length, reading speed and line limits.
- Click Validate.
- Fix the reported lines, for example with the SRT Formatter.
SRT Validator features
Syntax check
Numbers, timestamps and separators.
Timing errors
Reversed, overlapping and unsorted cues.
Readability
Line length, lines per cue and reading speed.
Line numbers
Every problem points to its line.
Report download
Save the result as a text file.
Private
Runs in your browser; nothing is uploaded.
When to use SRT Validator
- Checking files before uploading to YouTube, Vimeo or a streaming service.
- Quality control for translated subtitles.
- Finding why a player shows no subtitles.
- Reviewing subtitles produced by speech recognition.
SRT Validator FAQ
What makes an SRT file invalid?
Missing or wrong cue numbers, malformed timestamps such as 0:1:2,5, a dot instead of a comma before milliseconds, missing blank lines between cues, and cues whose end time is before their start time.
What reading speed is comfortable?
Professional guidelines usually allow 15–20 characters per second for adults; 17 is common for broadcast, 20 for streaming. Children’s content uses less.
Why are long lines a problem?
Lines over about 42 characters are hard to read and may be wrapped or cut by players. Netflix and the BBC use 42 and 37 characters as limits.
Does the validator change my file?
No. It only reports. Use the SRT Formatter to renumber, sort, re-wrap and fix timestamps automatically.
Which formats are supported?
SRT and WebVTT (.vtt), detected automatically. Open a file or paste the text.
Is my file uploaded?
No. Everything happens in your browser.
What a valid subtitle file needs
An SRT file is a sequence of blocks separated by blank lines. Each block has a sequential number, a timing line with start and end times in the form 00:01:02,345 --> 00:01:04,000, and one or more lines of text. WebVTT is similar but starts with a WEBVTT header, uses a dot before the milliseconds and allows optional cue settings and identifiers. Small deviations from these rules are surprisingly common, and players react differently: some skip a cue, some stop reading the file altogether.
The validator parses the file leniently, the way tolerant players do, and records every place where it had to recover: a missing number, a timestamp with the wrong separator, text before the timing line. These are reported as format issues with their line numbers, so they can be fixed in any text editor.
Next come timing checks. A cue that ends before it starts will never be shown. Cues that start before the previous one indicate a file that is out of order, often after merging two files, and overlapping cues make players show two subtitles at once.
Readability checks apply common professional limits that you can adjust: characters per line, lines per cue, a minimum display time and the reading speed in characters per second. These are warnings rather than errors – the file plays, but viewers may struggle to keep up.
Everything runs locally, so unpublished subtitles stay private.