Timing
Catch overlaps and broken timestamps
Jump directly to the source block responsible for each error.
Free SRT validator
Caption QA: SRT and VTT Checker
Caption QA. Open an SRT or WebVTT file, review every cue-level issue, preview timing against audio, and export a clean file. No signup and no caption upload.
Timing desk
Find subtitle problems before viewers do.
Checks run locally. Caption text and optional preview audio stay on this device.
Find and replace
Readability
Use adjustable delivery limits
Switch between Latin and CJK profiles or enter house-style limits.
Safety
Keep editorial decisions yours
No automatic retiming or rewriting. Every meaningful correction stays explicit.
The checks
What each flag means and how to fix it
Every cue is checked against the rules below. The numbers are the defaults for Latin scripts; the CJK profile changes the line and reading-speed limits, and you can type your own.
| Flag | When it fires | Usual fix |
|---|---|---|
| Invalid timestamp (error) | A time is not in HH:MM:SS,mmm (SRT) or HH:MM:SS.mmm (VTT) form. | Retype the time. A missing hour field or a colon instead of the comma is the usual cause. |
| Overlap (error) | A cue starts before the previous cue has ended. | End the earlier cue at or before the next start. Depending on the player, overlapping cues stack on screen or one of them is dropped. |
| Empty cue (error) | The cue has a time range but no readable text once formatting tags are removed. | Delete the cue or add the missing line. |
| Reading speed (warning) | More than 20 visible characters per second (12 for CJK). | Lengthen the cue into the gap after it, or shorten the wording. |
| Line too long (warning) | A line has more than 42 characters (20 for CJK). | Break the line at a natural phrase, not in the middle of a name or number. |
| Too many lines (warning) | The cue uses three or more lines. | Split it into two cues with their own times. |
| Short or long cue (warning) | On screen for under 1 second or over 7 seconds. | Under 1 second is hard to read; over 7 seconds usually means two thoughts that belong in separate cues. |
| Duplicate (warning) | The same text, ignoring case, appeared in an earlier cue. | Often a copy-paste slip after an edit. Keep it only if the line really is repeated. |
Captions made from AI narration often fail on reading speed, because a fast voice packs a long sentence into a few seconds. Slowing the voice slightly in the generator is often easier than rewriting the captions.
FAQ
Caption QA FAQs
01 What does the caption checker test?
It finds invalid timestamps, overlaps, empty or duplicate cues, long lines, fast reading speeds, unusually short or long cues, and captions using more than two lines.
02 Are my subtitles uploaded?
No. Parsing, validation, editing, preview, and export happen in your browser.
03 What reading speed should captions use?
The default is 20 visible characters per second for Latin scripts and 12 for CJK scripts. You can change both the reading-speed and line-length thresholds.
04 Does the tool automatically change subtitle timing?
No. Export safely normalizes cue numbering, spacing, and timestamp separators, but it never silently changes timing or wording.
05 Why is 42 characters per line the default?
It is a common house-style limit for Latin-script subtitles: two lines of about 42 characters fit across a 16:9 frame at a readable size. Chinese and Japanese characters are wider, so the CJK profile uses 20. If your client or platform publishes its own limits, type them in and every cue is re-checked.
06 Is a warning the same as an error?
No. Errors (invalid timestamps, overlaps, empty cues) can break playback or make a player skip a cue, so fix them before publishing. Warnings (reading speed, line length, cue length, duplicates, more than two lines) are readability checks; a short cue such as "No." or a deliberate repeated line can be fine.
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