Subtitle readability checker
Paste an SRT or VTT file and find the captions that read too fast, run too long, or use too many lines — before your viewers do. In your browser; nothing is uploaded.
Readable subtitles, by the numbers
A caption that's technically correct can still be unreadable if it flashes by too fast or crams in too much text. The four checks here — reading speed (characters per second), line length, lines per caption and minimum duration — are the same ones professional subtitlers and platform style guides use. Defaults follow common practice (17 CPS, 42 characters, 2 lines, 0.8s); tighten or loosen them for your platform.
Need cleaner subtitles to start with? Every Speecho transcription produces properly-segmented .srt and .vtt files — add captions to a video or transcribe a file. To re-time a file, use the subtitle timing shifter; to change format, the subtitle converter.
Readability checker — FAQ
What is CPS (characters per second)?
Reading speed: the caption's character count divided by how long it stays on screen. It's the main measure of whether a subtitle can be read comfortably. Common ceilings are 17 CPS for a relaxed pace, up to about 21 CPS for adults reading fast — Netflix, for example, uses 20 CPS for adult content and 17 for children's.
What are the usual subtitle limits?
Most style guides cap lines at about 42 characters, use at most 2 lines per caption, keep a caption on screen for a minimum of ~0.8 seconds, and stay under 17–21 CPS. These defaults are pre-set above and you can adjust them to your platform's guide.
Is my file uploaded?
No. The check runs entirely in your browser — your subtitle file never leaves your device and nothing is sent to a server.
How do I fix the flagged captions?
For high CPS, either shorten the text or extend the caption's duration. For long lines, break them into two shorter ones or trim filler words. If timings are simply off, the subtitle timing shifter can re-sync the whole file.