What is checked
Bounded syntax, timestamp order, overlap, declared media boundary, duration, gap, estimated reading speed, line count and length, cue IDs and WebVTT block coverage.
FREE SRT & WEBVTT CHECKER
Check SRT and VTT subtitles before you publish.
Move every caption earlier or later by the same amount, with a preview and undo. Find overlaps, edit individual captions or convert SRT and supported VTT. Your subtitle text stays in this tab; automatic speech synchronization is not provided.
- 1 · Add subtitles
- 2 · Check timing
- 3 · Review cues
- 4 · Download
- 5 · Check in your player
1. Add one subtitle file
UTF-8 SRT/WebVTT · maximum 5 MiB · 10,000 cues. Processing stays in this tab.
Examples are fictional. Choose one, then Analyze subtitles. The checks flag problems; they do not automatically repair timing or rewrite dialogue.
2. Choose your timing checks
Profiles are source-informed FastTool heuristics—not Netflix, BBC, WCAG or player compliance certificates.
Without it, out-of-media remains unverified.
Ready.
PASS
Know what each example should show.
These four fictional examples use the same checker as your own file. Each example sets the format, media duration and Balanced review profile for you. Choose its button above, then analyze.
| Example | What to notice | Expected result | What to do next |
|---|---|---|---|
| Clean captions | Three SRT cues end by 7 seconds in an 8-second clip, with space between captions. | PASS within the selected timing checks. | Download, then watch with your actual video. Passing text checks does not prove that speech is synchronized. |
| Find an overlap | Cue 2 starts at 2.5 seconds before cue 1 ends at 3 seconds. Cue 3 ends at 10.8 seconds, beyond the declared 10-second clip. | BLOCK: overlap and out-of-media findings. | Choose Edit caption 2, correct its start time and apply. Edit caption 3 to fit the actual clip, then recheck. Choose timings by watching the video; the tool will not guess synchronization. |
| Styled WebVTT | Two cues include dense text, a short gap, styling, a region and placement settings. | INDETERMINATE: reading and rendering review required. | Review the text pace and test styling in your target player. Do not remove layout information just to obtain a PASS. |
| VTT to SRT | Two plain WebVTT cues end at 4.8 seconds in a 6-second clip. There are no cue IDs, comments or layout features. | PASS within the selected checks; normalized VTT and a round-trip-checked SRT are available. | Choose Download SRT. Its first cue stays at 0–2 seconds and the second at 2.4–4.8 seconds; text and cue order are unchanged. |
These are demonstration outcomes, not customer results or platform certification. Optional technical reports remain available with your own result.
Fix the caption, not just the warning
- Analyze your file. Search across every caption, filter to captions with findings, or page through the list. The checker supports up to 10,000 captions within its 5 MiB input limit.
- Select Edit caption. Enter the start and end as
HH:MM:SS.mmm, and edit the dialogue or line breaks. Adjacent timings are shown for context, not as suggested fixes. - Choose Apply caption and recheck. Only that caption changes; every other caption, plus WebVTT notes, styling and layout settings, is retained in the working copy. Download buttons stay locked while a draft is unapplied.
- Inspect the new findings and download the current SRT or VTT. Undo last applied edit restores one previous working copy and runs the checks again. Your original local file is never overwritten.
Edits are manual, not automatic audio alignment. Blank lines cannot be inserted inside a caption because they create new blocks. Invalid intervals, out-of-video edits, malformed WebVTT and inline timestamps outside the new cue interval are rejected without applying the edit. Remaining overlaps and reading-speed warnings stay visible. Watch the exported file in your actual player before publication.
YouTube's caption text and timestamp editing workflow · W3C guidance on caption review. These sources describe real caption-editing needs; this tool does not claim platform certification.
How to convert SRT to VTT—or VTT to SRT
- Paste your text or choose a subtitle file. Enter the exact video duration if you know it.
- Select Analyze subtitles. Resolve timing problems before publishing; files marked review copy still need attention.
- Choose Download VTT for SRT input, or Download SRT for supported plain WebVTT. Each conversion is parsed again to check cue text, timing and order.
WebVTT can carry information SRT cannot represent here. Cue IDs, comments, header metadata, styling, regions, positioning and cue markup keep SRT conversion unavailable. The result explains which features were found. Keep the original; do not remove meaningful information merely to enable a download.
SRT-to-VTT conversion preserves plain text and balanced <b>, <i> and <u> formatting, including nested spans and line breaks. It does not turn those tags into visible dialogue. Color, positioning, unsupported tags and player-dependent SRT entity notation stop conversion with an explanation; the same-format download remains available.
Literal WebVTT text such as <i> must not silently become active SRT formatting. Ambiguous text stays in WebVTT. A sole speaker span may omit its closing voice tag; it remains unchanged in the WebVTT download. These checks preserve the supported text and styling representation, not identical appearance in every player.
Fix subtitle overlap, understand reading-speed warnings and choose the right download.
What is not claimed
No OCR, audio alignment, translation quality, target-player rendering, accessibility certification or Netflix/BBC compliance claim. STYLE, REGION and cue layout settings require review.