Subtitle guideline checker
Line length, reading speed, how long each cue stays on screen, overlaps and gaps — measured cue by cue against one rule set, so you can see which cues actually fail instead of guessing. The file never leaves your browser.
Drop an .srt / .vtt / .ass file here
or click to choose one · the report is shown below, nothing is uploaded
Which rules are being broken
Cue by cue
The thresholds, written out
| Rule set | CPL | CPS | Min duration | Max duration | Max lines | Min gap |
|---|---|---|---|---|---|---|
| Netflix Timed Text Style Guide published | 42 | 17 | 833 ms | 7000 ms | 2 | 83 ms |
| YouTube indicative | 42 | 21 | 700 ms | 7000 ms | 2 | 80 ms |
| TikTok / short form indicative | 32 | 20 | 500 ms | 5000 ms | 2 | 40 ms |
| Loose — hard errors only indicative | 60 | 30 | 300 ms | 12000 ms | 3 | 0 ms |
CPL = longest line in characters. CPS = characters per second of reading speed. Durations are per cue. The gap is the blank space between one cue ending and the next starting — a gap below two frames tends to flicker on some players.
How each rule is computed
| Check | Measured as | Why it matters |
|---|---|---|
| CPL | Characters in the longest line of the cue | Long lines get cut off or shrink to unreadable size on phones |
| CPS | All characters in the cue ÷ its duration in seconds | The viewer simply cannot finish a line above their reading speed |
| Min duration | Cue end − cue start | Under a few hundred milliseconds the cue reads as a flash |
| Max duration | Cue end − cue start | A cue that stays for many seconds is usually two cues that were not split |
| Overlap | Cue start earlier than the previous cue's end | Two cues on screen at once: players render one and drop the other |
| Out of order | Cue start earlier than the previous cue's start | Breaks binary-search playback and burn-in tools |
| Zero/negative duration | Cue end ≤ cue start | Never displayed at all; usually a re-cut or frame-extraction error |
Checking a whole season?
The studio runs the same checks on every open file and can export the findings as a CSV or JSON report you can attach to a delivery. Pro is a $9 one-time licence — lifetime, up to 3 devices — with a 7-day refund while the key is unactivated. Checking one file, with the full findings listed here, stays free.
Questions people ask before using it
What is CPS in subtitling?
Characters per second — the number of characters a viewer has to read divided by how long the cue stays on screen. 17 characters per second is the value used by the widely published Netflix timed-text style guide; above that most viewers cannot finish the line.
Are these guideline values requirements?
Only when a platform or a client has told you they are. Published style guides give real numbers that are widely used as a default; the YouTube and short-form presets here are industry rules of thumb, not official rules. The tool labels which is which — the point is one ruler for the whole file.
Does the checker fix the problems too?
No, it only measures. Fixing means re-timing a cue, splitting a long line or shortening text, which is editorial work. The studio applies the mechanical fixes (shift, stretch, split) once you know which cues need them.