Paste or open an SRT or WebVTT file to check every subtitle's reading speed in characters per second, plus line length, line count, time on screen and overlaps. Defaults follow Netflix's published English limits, and you can set your own. Everything runs in your browser.
Nothing is uploaded. The check runs in your browser.
Subtitles
3
Within limits
67%
Flagged
1
Average speed
34.0 CPS
Fastest
#2 · 67.5 CPS
#
Time
Text
CPS
Issues
2
00:00:03.400 0.80 s
This one flashes past far too quickly to read in time.
Paste your subtitles or open an .srt or .vtt file.
Pick a standard, or choose Custom and set your own limits.
Fix flagged subtitles in your subtitle editor: shorten the text, give it more time, or split it differently. Then check again.
Captions for social video
Short-form video rarely uses subtitle files. Most TikTok, Reels and Shorts captions are burned in and timed word by word, two or three words at a time, which keeps reading speed comfortable even for fast talkers. In Valmera you upload a video and ask for captions, and the AI agent times every word to the audio and styles it. Creating an account and uploading are free; editing requires a subscription.
Frequently Asked Questions
Netflix's English (USA) style guide allows up to 20 characters per second for adult programs and up to 17 for children's programs. Other broadcasters and platforms publish their own limits, so use the standard your client or platform requires. Slower is always easier to read, especially for longer lines.
CPS is the number of characters in a subtitle divided by how many seconds it stays on screen. This checker counts letters, numbers, spaces and punctuation, and skips line breaks and formatting tags such as <i> or {\an8}. A 40-character subtitle shown for 2 seconds is 20 CPS.
Netflix's English guide sets 42 characters per line and a maximum of two lines. Shorter lines are easier to read on phones, and vertical social video usually needs much shorter lines than TV.
Netflix's general requirements set a minimum of 5/6 of a second (20 frames at 24 fps) and a maximum of 7 seconds per subtitle event. The checker flags anything outside those limits.
Shorten the text by cutting filler and repetition, extend the subtitle into a silent gap, or merge it with a neighbour and split the text differently. Avoid stretching a subtitle so it overlaps the next one, because that is flagged too.
No. The file is read and analyzed in your browser and never leaves your device.
No. Valmera burns word-timed captions into the video instead of exporting subtitle files. Use this checker for subtitle files from any other source, and the subtitle timing shifter or SRT to VTT converter to fix their timing or format.