Drop a subtitle file and see every problem with its line number, from timestamps a player will reject to captions too fast to read. One click writes a repaired file. It runs in this tab, so the file is never uploaded.
| Check | Why it matters | Fixed automatically? |
|---|---|---|
| Timing line readable | A typo in 00:00:01,000 --> 00:00:04,000 makes most players skip the cue, and some stop reading the file there. | Reported (the cue is dropped from the fixed file) |
| Comma before the milliseconds | SRT uses a comma, VTT a dot. An SRT with dots is the most common reason a file loads with no captions. | Yes |
| End after start | A cue that ends before it starts flashes for one frame or never shows. | Yes, given a length from its text |
| Time order and overlaps | Players expect cues in order. Overlapping cues stack on screen, two at once. | Yes |
| Numbering 1, 2, 3 | Gaps and repeats confuse strict readers: some TVs, broadcast and editing software. | Yes |
| Stray text block | A blank line inside a cue cuts it in two; the second half has no timing. | Yes, joined to the cue above |
| WEBVTT header | Browsers refuse a .vtt without it. | Yes |
| UTF-8 and byte-order mark | Files from old Windows editors are Windows-1252; accents turn into junk on the web. | Yes, saved as UTF-8 |
| Line length, line count | Long lines wrap or run off phone screens. | Reported, you choose the words |
| Reading speed (characters per second) | Above the limit, viewers cannot finish reading before the caption changes. | Reported |
| Duration | Under about 0.8 s most viewers miss it; over 7 s it usually should be split. | Reported |
The default limits come from Netflix's public style guides, checked on 2026-10-26: 42 characters per line and up to 20 characters per second for adult programmes, 17 for children's, in the English (USA) guide; at most 2 lines, at least five-sixths of a second and at most 7 seconds on screen in the general requirements. YouTube, Vimeo and social platforms are more lenient; broadcasters are often stricter. Change the limits above to match where the file is going.
The format itself is explained, with an annotated example, on the SRT file format and the VTT file format. To move every caption earlier or later, or join the subtitle files of a recording that was split into parts, use merge and shift subtitles. For the words alone, SRT to TXT rejoins the captions into paragraphs.
The usual causes are a timing line with a dot before the milliseconds (00:00:01.000 instead of 00:00:01,000), a cue whose end time is before its start, cues out of time order, a blank line inside a cue that splits it in two, or a file saved in an encoding other than UTF-8. The checker lists each with its line number, and Fix repairs all of them.
Blocks separated by one blank line. Each block is a sequence number, a timing line in the form 00:00:01,000 --> 00:00:04,000 with a comma before the milliseconds, then one or two lines of text.
Netflix's English style guide sets 42 characters per line, at most 2 lines, and a reading speed up to 20 characters per second for adult programmes (17 for children's). Its general requirements keep each subtitle on screen for at least five-sixths of a second and at most 7 seconds. The checker uses these numbers by default and lets you change them.
No. The file is read and checked by JavaScript in this browser tab. Nothing is sent to WhipScribe or anyone else.
No. It changes structure only: numbering, the time format, cue order, overlapping or reversed end times, empty cues, stray text blocks rejoined to their cue, the byte-order mark and the encoding. Lines that are too long or too fast are reported for you to edit, because shortening them means choosing words.
Start from the recording and download the subtitle file: see the SRT file generator, YouTube to SRT and a VTT caption file for web players.