A quiet workspace. A clear review.
1. Open a track
Choose, drop or paste UTF-8 SRT or WebVTT. The limit is 2 MB and 10,000 captions per track. Try the sample project to explore.
2. Review findings
Choose Start review or Needs review, then move through findings with Next issue and Previous issue. Filter by issue type when needed. Edit text and timestamps, then save to recheck. Findings are prompts to inspect, not instructions to rewrite dialogue.
Read the status colours
Red marks errors that need correction. Amber marks timing or readability findings for human review. Blue marks safe cleanup you can preview. Green means no findings under the current rules, not a guarantee of translation accuracy or delivery compliance. Every state has a symbol and label; colour is never the only cue. Click a summary card to filter captions.
3. Correct carefully
Preview safe fixes to inspect whitespace trimming and numbering repair. Automatic fixes do not retime, rewrite, delete, split or merge cues. For a long, single plain-text line, Suggest a line break offers a two-line preview. It preserves words and timing and remains a draft until you save. Formatting tags, existing multiple lines and impossible two-line fits require manual editing. Save & next saves the selected caption and opens the next affected caption. Undo restores the previous state. Source errors block subtitle export until repaired in the Source editor. Export always makes sequential SRT numbers.
Shift a consistently early or late track
Open Shift timing, enter a signed offset in seconds, inspect the preview, then apply. Positive values move later; negative move earlier. Text and durations stay intact. Invalid files and shifts before zero are blocked. Undo restores the previous timing.
4. Compare another language
Choose Compare tracks and upload or paste a reference. In the demo, Try the Arabic demo loads the example translation with one click. Only show differences hides aligned groups. Long comparisons show 100 groups per page; downloaded reports include every group. Connected groups match by overlapping time intervals, including split, merged and many-to-many segmentation. Under 70% coverage on either track is marked partial; group boundary differences above 250 ms are marked for timing review. Both coverage percentages are shown. Invalid durations are errors, not alignment results. Starts within 250 ms may be suggested only for cues without any overlapping match; these suggestions do not reuse an already matched cue. No translation accuracy is assessed. Malformed tracks give incomplete comparisons.
5. Review local video
Load a local video and click a caption to seek. Filtering, editing and switching workspaces preserve the loaded player. Video stays on your device. Playback depends on browser codecs; no transcoding occurs. The overlay renders plain text, not advanced styles or positioning. This is review playback, not video export.
6. Export and hand off
Export SRT, WebVTT and HTML or JSON reports. A readiness panel distinguishes blocking errors, remaining review findings and a clear track. When errors block subtitles, reports and the original source remain downloadable; Go to errors opens the relevant repair view. WebVTT-to-SRT conversion requires acknowledgement of lost metadata, cue settings, identifiers and style semantics. Reports include file contents; share client work carefully.
Rules and standards
Starting values: 20 visible characters/second, 42 characters/line, 2 lines, 0.834–7 seconds duration and an 80 ms short-gap threshold. Characters are Unicode grapheme clusters, including spaces and punctuation, excluding markup. These are adjustable heuristics informed by English adult-programme guidelines, not a compliance preset. Arabic and other languages need language-specific limits.
See Netflix general requirements, language-specific guides, and the WebVTT specification. CaptionCheck is independent.
Keep edits safe
An unsaved caption edit is protected when you switch views or captions. Save and recheck before moving on. Use Command/Ctrl+S to save, or Alt+Up/Down to navigate issues. The line-length meter updates as you type. Closing or refreshing the tab still loses in-memory work, so export a copy to keep it.
Boundaries
No transcription, translation evaluation, audio sync, waveform editing, shot-change detection or delivery certification. WebVTT metadata and settings are preserved on same-format export but not fully validated. Advanced authoring belongs in a full subtitle editor. Changes are held in this tab only; export to keep your work.