InputTestHub

Caption Accessibility Checker

Checks a subtitle file for captions that are too fast to read, lines that are too long, cues that are too brief and overlapping timings.

SEO Nothing uploaded No sign-up Free, unlimited
SEO tool
17 for adults, 12–14 for children
Paste something on the left to see the result.
In short Caption Accessibility Checker is a free online tool on inputtesthub.com that checks a subtitle file for captions that are too fast to read, lines that are too long, cues that are too brief and overlapping timings. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.

How to use the Caption Accessibility Checker

  1. Paste your code into the input area.
  2. Choose the indentation and output options you want.
  3. Read the formatted result, then copy or download it.

About the Caption Accessibility Checker

The Caption Accessibility Checker checks a subtitle file for captions that are too fast to read, lines that are too long, cues that are too brief and overlapping timings. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.

What people use it for

  • Checking auto-generated captions before publishing.
  • Meeting a broadcaster or platform caption specification.
  • Finding the cues that flash past too fast to read.

Details

Adult limit≈ 17 characters a second
Children12–14
Line length≈ 42 characters
Lines per cueTwo
Minimum on screenAbout one second

The maths behind it

This tool uses reading speed is characters excluding spaces divided by the seconds the cue is on screen, which is the measure broadcasters use rather than words per minute. Every intermediate value is shown on screen, so the result can be checked by hand.

WCAG 1.2.2 requires captions to exist and says nothing about whether they can be read in the time available — which is where most caption files actually fail. None of these measures appear in an automated conformance check.

Where this tool stops

It measures timing and length. It cannot judge whether speaker changes are marked, whether sound effects are described, or whether the text matches what was said — all of which matter as much and need a person.

Frequently asked questions

My captions pass a validator but people say they cannot read them. Why?
Because validators check the file format and nothing about whether a human can read the text in the time given. Auto-generated captions in particular follow speech exactly, so a fast speaker produces cues at 25 characters a second — well-formed, and unreadable. That is what this measures.
Why 42 characters and two lines?
It is the shape broadcast subtitling settled on. A third line covers too much of the picture, and beyond about 42 characters the eye movement back to the start of the next line costs more time than the reader has. Both are conventions rather than WCAG requirements, which is why they are adjustable here.
Do I need an account to use the Caption Accessibility Checker?
No charge and no sign-up. There is no free tier to run out of because there is no paid tier — inputtesthub.com is funded by advertising rather than by metering the tool.
Can you see what I put into this tool?
No. The Caption Accessibility Checker runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
Can I check the maths myself?
It uses reading speed is characters excluding spaces divided by the seconds the cue is on screen, which is the measure broadcasters use rather than words per minute. The full working is printed under the result, so you can follow every step rather than trusting a black box.
What problem does the Caption Accessibility Checker solve?
In practice it gets used for three things: checking auto-generated captions before publishing. Meeting a broadcaster or platform caption specification. Finding the cues that flash past too fast to read. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is there anything the Caption Accessibility Checker cannot do?
It measures timing and length. It cannot judge whether speaker changes are marked, whether sound effects are described, or whether the text matches what was said — all of which matter as much and need a person. Knowing where a tool stops being trustworthy matters more than the cases where it works.
What figures does the Caption Accessibility Checker work from?
Adult limit is ≈ 17 characters a second. Children is 12–14. Line length is ≈ 42 characters. These are printed on the page itself, so you do not have to take them on trust.
Will this work on a tablet?
Yes. The page is responsive and the tool works in Chrome, Safari, Firefox, Edge and Samsung Internet on both Android and iOS. There is no app to install and nothing to sign into.

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