Subtitle Timing Checker

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Quick answer

A timing checker audits a subtitle file against professional readability rules and flags every cue that breaks one. It measures reading speed in characters per second, checks each cue’s duration and line length, verifies a minimum gap between cues, and highlights overlaps. You get the full list of problem cues, a CSV report to pass on, and a one-click fix for the mechanical problems — start times never move and nothing is reworded. The audit runs in your browser and nothing is uploaded.

Step by step

How to subtitle timing checker

01
Load the file to audit
Drop your .srt, .vtt or .ass file in, or paste it. Every cue is parsed with its text and timing ready to measure.
02
Review the flagged cues
The checker reports each cue that reads too fast, sits on screen too briefly or too long, runs too wide, crowds its neighbour or overlaps it — with the measured value beside each rule.
03
Export or fix
Export the list as a CSV report, or press “Fix what can be fixed safely”. The fix only moves end times, into free time: it ends overlaps before the next cue starts, extends cues that are too short or too fast, trims cues that linger, and re-breaks over-long lines. Anything left (rewording, splitting a cue) stays listed so you can finish it in the editor.

In depth

Which rules does it check, and why?

These are the readability guidelines broadcasters and subtitling houses have converged on. None is arbitrary — each maps to a limit of how fast the eye can read a caption while still watching the picture.

The readability rules the checker enforces.
Rule	Typical threshold	Why it exists
Reading speed	≤ ~17–20 CPS (characters/second)	Above this a viewer cannot finish the line before it disappears
Minimum duration	≈ 0.8–1 second	Shorter than this and the eye cannot even land on the text
Maximum duration	≈ 7 seconds	A caption that lingers longer reads as frozen or stuck
Line length	≤ 42 characters per line	Longer lines wrap badly and force the eye too far across
Minimum gap	≥ 83 ms (2 frames at 24 fps)	A visible flick of blank between cues stops them blurring together
No overlaps	Cue must end before the next begins	Overlapping cues fight for the same screen space

Reading speed (CPS)

The headline metric. It divides a cue’s character count by its on-screen duration — letters, spaces and punctuation all count, formatting tags never do: a 60-character line shown for 3 seconds is 20 CPS. Keep it at or below roughly 17–20 CPS — professional targets sit around 17 for general audiences and allow a little more for adults — so viewers can read the line and still watch the scene.

Duration, length and gap

A cue under about 0.8–1 second flashes past before the eye settles; over about 7 seconds it reads as stuck. Lines beyond 42 characters wrap awkwardly on small screens. And consecutive cues need a small gap — around two frames at 24 fps (83 ms, the checker’s default) — so the viewer perceives a change instead of one caption smearing into the next.

How do you fix a flagged cue?

The checker diagnoses; it does not rewrite. To clear a fast-reading cue you either give it more time (extend its end, if there is room before the next cue) or shorten the text. Over-long lines are split across two lines or trimmed. Overlaps and gap violations are fixed by moving an end or start time. Make these changes in the subtitle editor, then run the audit again to confirm the file is clean.

Is the file uploaded to check it?

No. Every measurement — character counts, durations, gaps, overlaps — is computed in your browser over the parsed cues; nothing is transmitted. Watch the Network tab in DevTools during a check and you will see no request. Confidential scripts and pre-release captions stay on your machine.

Fix the flagged cues in the subtitle editor; if a whole file reads fast because it drifted, the subtitle sync fixer may be the real cause. When the audit is clean, add the subtitles to your video with confidence they are comfortable to read.

Your files never leave your device

Processed locally in your browser — nothing is uploaded. You can verify it yourself: open your browser’s developer tools, watch the Network tab, and use the tool — no upload request is ever made.

No file is ever uploaded to a server
Works offline after the first visit
No account, no watermark, no limits

A little more clarity

Frequently asked questions

What is a good reading speed for subtitles?

Aim for about 17–20 characters per second. Around 17 CPS suits general audiences; a little higher is acceptable for adult content. Above roughly 20 CPS most viewers cannot finish reading before the cue changes.

How is CPS calculated?

The characters in the cue — letters, spaces and punctuation, but not formatting tags — divided by how many seconds it stays on screen. A 60-character caption shown for 3 seconds is 20 CPS.

How long should a caption stay on screen?

Between about 0.8–1 second at the minimum and about 7 seconds at the maximum. Too short and the eye cannot land on it; too long and it reads as stuck.

Why does the checker flag a gap between cues?

Consecutive captions need a small gap — about two frames at 24 fps, which is 83 ms by default — so the viewer perceives a change. Without it, one cue appears to smear into the next.

What counts as an overlap?

A cue whose end time is later than the next cue’s start time. The two would show at once, competing for the screen, so the checker flags it to fix.

Does the checker fix the problems automatically?

Yes, the mechanical problems. “Fix what can be fixed safely” only ever moves end times, into free time: it ends overlapping cues before the next one starts, extends cues that are too short or too fast, trims cues that stay up too long, and re-breaks lines that run past the limit. Start times never move and the wording is never touched. What is left — a line that needs rewording or a cue that needs splitting — stays listed so you can fix it in the subtitle editor.

Why is 42 characters the line-length limit?

It is the widely used broadcast maximum that keeps a single line readable without wrapping badly or forcing the eye too far across small screens.

My whole file reads too fast — what does that mean?

If nearly every cue is over the CPS limit, the timing may have drifted so cues are too short. Check whether a frame-rate mismatch is compressing the timing before editing cues one by one.

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