What the checks mean
Try it: can you read this subtitle in time?
Change the text or how long it stays on screen, then flash it. Reading speed = characters ÷ seconds on screen.
58 characters need at least 3.4 s at 17 characters per second. If the speaker does not give you that long, shorten the line: viewers read subtitles more slowly than people speak.
| Flag | Rule | Why |
|---|---|---|
| characters/s over 17 | Reading speed | Netflix uses 17 cps for adult English content and the BBC suggests roughly 160 to 180 words per minute; faster lines disappear before most people finish reading. |
| Line over 42 characters, or 3+ lines | Line length | Long lines force the eye to travel and can run off small screens. |
| On screen under 0.8 s | Minimum duration | Too short to register, even for one word. Most style guides use 5/6 of a second to 1 second as the floor. |
| On screen over 7 s | Maximum duration | Viewers re-read lines that linger; split them. |
| Overlap | Timing | Many players show only one cue, or stack them awkwardly. |
Keyboard and editing tips
- Click a line to select it and jump the video there; the selected line gets its own toolbar.
- “Start here” and “End here” copy the playhead time, the fastest way to fix timing by ear.
- Timecodes accept
00:01:02,500,1:02.5or62.5-style input with a colon; press Enter or leave the field to apply. - Undo keeps the last 40 changes. The whole project auto-saves in this browser and can be restored after closing the tab.
- With the video focused on the timeline, the left and right arrow keys move one second.
Questions people ask
How do I edit an SRT file online?
Open the file above (or drag it in). Edit text in the list, change timecodes directly or with “Start here” and “End here”, then press “Download .srt” in the Export tab.
Is my subtitle file uploaded?
No. The file is read and edited in your browser, and an autosave copy is kept in your browser's local storage until you clear it.
Can I shift all subtitles at once?
Yes: open “Timing & bulk tools” below the list and enter a shift in seconds. For drifting subtitles use the Subtitle sync tool, which can stretch timing as well.
Can I edit a VTT or ASS file?
Yes. SRT, WebVTT, YouTube SBV, ASS/SSA and plain text all open in the editor and can be saved in any of those formats.