Subtitle Checker & Fixer – SRT / WebVTT Validator, Reading Speed (CPS) & SRT to VTT Converter

Validate subtitle files before delivery to a film festival, distributor, Netflix-style platform or client. Paste text or give SRT/VTT URLs; get a per-cue error report, a safely fixed SRT and a WebVTT (.vtt) export. Works in batch from the Apify API, Make, n8n or Zapier. No install, no subtitle editor needed.

Built by a professional subtitler and film editor (OpenSubtitles contributor since 2014).

What it checks (per subtitle)

• Characters per line (CPL) and number of lines
• Reading speed (CPS, characters per second)
• Minimum / maximum duration, zero or negative durations
• Overlapping subtitles and gaps shorter than 2 frames
• Empty cues, broken numbering, malformed timecodes

Auto-fix (never rewrites your text)

Removes overlaps, enforces the minimum gap, renumbers cues, normalises timecodes, and exports SRT → VTT.

Presets (based on public style guides)

Preset	CPL	Lines	CPS	Min / max duration
festival-default	42	2	17	0.833 s / 7 s
netflix-en	42	2	20	0.833 s / 7 s
netflix-en-children	42	2	17	0.833 s / 7 s
bbc	37	2	17	1 s / 7 s
Every rule can be overridden. Always check your client's own spec.

Great for

• Checking AI / Whisper-generated subtitles before publishing (auto captions often break CPS and overlaps)
• Festival submissions (FilmFreeway) that require English SRT
• Translators and subtitling agencies doing batch QC
• Developers needing an SRT validator API or SRT to VTT converter API

Output (one row per file)

cues, errors, warnings, issues[] (cue number, rule, value, limit), issues_after_fix, fixed_srt, fixed_vtt.

Pricing (pay per event)

$0.01 per subtitle file checked (fixed SRT and VTT included).

Keywords: subtitle checker, SRT validator, VTT validator, subtitle QC, subtitle quality check, reading speed checker, CPS calculator, subtitle overlap fixer, fix SRT timing, SRT to VTT converter, WebVTT converter, Netflix subtitle guidelines, closed captions QC, sottotitoli controllo, sous-titres vérification.

Example

Input:

{"subtitleUrls": ["https://example.com/my-film.en.srt"], "preset": "netflix-en", "fix": true}

Output (shortened):

{"source": "https://example.com/my-film.en.srt", "cues": 812, "errors": 14, "warnings": 31,
 "issues": [{"cue": 57, "rule": "cps", "value": 23.4, "limit": 20}, {"cue": 58, "rule": "overlap", "value": -120, "limit": 0}],
 "issues_after_fix": 9, "fixed_srt": "1\n00:00:01,000 --> ...", "fixed_vtt": "WEBVTT\n\n00:00:01.000 --> ..."}

Download results as JSON, CSV or Excel from the dataset, or call the Actor via API and read fixed_srt directly.

🇮🇹 In italiano

Controllo qualità sottotitoli SRT/VTT prima della consegna a festival, distributori o piattaforme: caratteri per riga, velocità di lettura (CPS), durata minima/massima, sovrapposizioni e gap. Correzione automatica delle sovrapposizioni e della numerazione (il testo non viene mai modificato) ed esportazione SRT → VTT. Ideale per verificare sottotitoli generati con AI/Whisper. Prezzo: 0,01 $ per file controllato.