Useful Commons

Free browser tool

Check subtitle timing and reading speed

Paste or drop an SRT file and see every cue that reads too fast, has long or extra lines, is shown too briefly or too long, or overlaps another. Text is never rewritten for you: your own edits change the WebVTT only after you approve them.

Runs on this device. No upload, account or tracking.

Your subtitles

UTF-8, read on this device
    Empty

    Numbered cues with HH:MM:SS,mmm --> HH:MM:SS,mmm timestamps.

    Review

    Review never changes the file. Apply needs your edits and the review digest shown after a review.

    Thresholds, edits and approval (JSON)
    Empty

    Keys: config (max_chars_per_second, max_line_chars, max_lines, min_duration_ms, max_duration_ms), edits ([{"ref": "C0001", "end_ms": 2200, "note": "…"}]) and, in apply mode, approval ({"approved": true, "review_digest": "…"}).

    Up to 200,000 characters and 5,000 cues. Defaults: 17 characters per second, 42 characters per line, 2 lines, 1 to 7 seconds on screen. These are measurements against those numbers, not an accessibility or platform certification.

    About this tool

    What this tool does

    Check SRT subtitles for reading speed, line length, line count, display duration, overlaps and cue order against thresholds you set, then export WebVTT with only the edits you approve.

    Limits and safe use

    Up to 200,000 characters and 5,000 cues. Defaults: 17 characters per second, 42 characters per line, 2 lines, 1 to 7 seconds on screen. These are measurements against those numbers, not an accessibility or platform certification. Diagnostics are suggestions for a reviewer. Nothing is rewritten automatically, speakers are not inferred, and nothing is sent to a server or a model.