Caption compatibility checker

How to read the result

The same caption can be counted at two different lengths on two networks. That is why the check reports per platform — the limits differ, and so does the unit being counted.

A character is not what the reader sees

Most networks cap text on the unit the browser counts (a UTF-16 code unit). Bluesky caps on what a reader perceives as one character — a grapheme. A single emoji is 1 to a reader and can be 11 code units.

Why that matters

A naive counter can tell someone who wrote 28 characters that they wrote 300, blocking a post the server would accept. The mirror case is worse: text passes here and is rejected after the content has been scheduled.

Where the rule comes from

This tool does not decide which unit applies. The flag comes from the same server-side validators that run at publish time, so the result here cannot disagree with the rule being enforced.

If you are over the limit

Rather than rewriting per network, a common approach is to write to the tightest limit and move the longer explanation into the first comment. The check shows which platform is the constraining one.