What the subtitle quality checker does
Validate pasted or loaded subtitle content against a selected QC profile or your own thresholds. The report covers timing, reading speed, layout, numbering, tags, whitespace, and optional dictionary-based spelling checks.
How to validate a subtitle file
- Paste content into Paste subtitle content below, or drop/upload a subtitle file.
- Choose a format: Select SRT for SRT input or WebVTT for WebVTT input. Auto-detect recognizes a file beginning with
WEBVTT. SRT timestamps use commas, such as00:00:01,000; WebVTT timestamps use periods, such as00:00:01.000. - Choose a profile: Select Netflix (English, approximate), BBC guidelines (approximate), Generic / relaxed, or Custom. Custom enables the threshold fields for reading speed, line length and count, cue duration, and gaps.
- Optionally load a
.txtor.dicdictionary with one word per line. Spelling checks are skipped until a dictionary is loaded. - Review the validation report as it updates automatically when the source or settings change.
What the report checks
The report checks CPS, WPM, line length, line count, cue duration, gaps, overlaps, ordering, numbering, empty cues, timestamps, tags, and whitespace. Issues are shown with a severity level, cue details, and a suggested fix.
Whitespace checks cover leading or trailing line whitespace, repeated spaces, tabs, and the literal mojibake pattern  , plus leading or trailing blank cue lines. Dictionary spelling checks compare words with the loaded word list. Unmatched words are informational, and suggestions are not applied automatically.
Malformed cue blocks appear as parse issues and are excluded from later cue-level checks. A parse error can therefore leave some rules without results for that block.
Review, export, and correct the subtitle file
Review each report row, including its cue number, timestamp, rule, severity, issue, and suggested fix. Suggestions are text only and are not applied to the source automatically.
- Select Export JSON or Export CSV to save the report.
- Select Preview corrected file to generate the optional corrected output.
- Review the preview, then select Download corrected file if you want to save it.
The corrected output is serialized from successfully parsed cues. It preserves their timestamps and cue order, normalizes whitespace, renumbers serialized SRT cues, and appends closing <b>, <i>, or <u> tags when needed. Malformed or excluded blocks are not included. WebVTT metadata blocks such as NOTE, STYLE, and REGION may also be omitted.
Limitations and processing notes
This page reads subtitle and dictionary files in your browser. Its local code does not send those files in an upload request.
Files larger than 400,000 characters are truncated in the textarea preview, while the full source remains available for the initial validation. Avoid editing a truncated preview unless you intend to replace the full source with the displayed text.
This tool validates and reports on existing subtitle text. It does not translate content into another language or render, burn, or overlay captions onto a video file.
Frequently Asked Questions
Does this tool upload my subtitle file anywhere?
This page reads subtitle and dictionary files in your browser. Its local code does not send those files in an upload request.
What do the QC profiles change?
A profile pre-fills the reading-speed, line-length, line-count, cue-duration, and gap thresholds with commonly used approximate values. Selecting Custom unlocks every threshold so you can set your own numbers.
How does the spelling check work?
Spelling checks only run if you load a local dictionary file (one word per line, plain text). Words in the subtitle text that aren't found in that dictionary are flagged as informational issues - nothing is corrected automatically.
Does this tool fix my subtitles automatically?
No. Every issue in the report includes a suggested fix as text only. A corrected file is only generated when you explicitly click to preview it, and it only applies safe, non-destructive formatting fixes - whitespace cleanup, sequential renumbering, and closing unclosed <b>, <i>, and <u> tags. It never changes wording, timestamps, or cue order.
Does this tool translate subtitles or burn them into video?
No. This tool only validates and reports on existing subtitle text. It does not translate content into another language and does not render or burn captions onto a video file.