How to Validate Subtitle Files Before Delivery

Run through this checklist before handing subtitle files to a client or uploading them to a platform.

1. Structure

• Every cue has a number, a timing line, text and a trailing blank line
• Numbers start at 1 and increase by 1
• No empty cues

2. Timestamps

• All timestamps match HH:MM:SS,mmm
• Every end time is after its start time
• Cues are in chronological order
• Overlaps are intentional, or removed

3. Readability

• Lines within the agreed length
• No more than the agreed number of lines per cue
• Reading speed and display times within the agreed rules

4. Encoding and format

• UTF-8 encoding
• Correct extension (.srt, .vtt)
• WebVTT files start with WEBVTT

5. Naming and packaging

• File names match the videos and the agreed convention
• One subtitle file per video, per language, per format

6. Playback spot-check

Load the file in the target player and spot-check the beginning, middle and end. Automated validation can't tell you whether text matches speech — only watching (or listening) can.

Automate what you can

Steps 1, 2 and most of 3 and 4 can be automated. Paste a file into our SRT validator to try it, or download a sample validation report to see what a full report covers.