Free tool
Publish Guard — check a post before you send it
The same preflight check postfast runs inside its composer, running here in your browser. Paste a post, choose the networks it is aimed at, and every problem is named — the ones that will stop it and the ones that only might.
0 characters
Separate each reply with a blank line.
Nothing to check yet — paste a post and pick at least one network.
How this works
- It is the product’s own checker. This page imports the same shared module postfast’s composer renders from and its API refuses on. There is no second copy of the rules here, so what this says is what postfast would say.
- Blocking findings are certainties. A post with no body, a thread aimed at a network with no self-reply, an Instagram target with no media — these are refusals, not opinions.
- Character counts are warnings on purpose. X weights links and CJK characters, Bluesky counts graphemes, and neither weighting is modelled. A count a few over the limit may well publish, so this warns rather than blocks.
- Media is counted, not inspected. The checker knows how many items a post carries and which networks accept that many. It reads the count rather than the files themselves.
- It runs here, in your browser. No request is made, nothing is stored, and nothing is logged. Close the tab and it is gone.
Common questions
- What does this actually check?
- Character limits per network, missing media where a network demands it, threads aimed at networks with no self-reply, too many media items or thread replies for a network, and empty parts of a thread.
- Why is my 285-character X post only a warning?
- Because X does not count characters the way your editor does — a URL counts as a fixed-width t.co link and CJK characters count double. A count near the limit may publish, so refusing it would be a guess overruling you.
- Does it check images and videos?
- It counts them, and checks that count against what each network accepts on one post — including Instagram, which refuses a caption with nothing attached.
The other free tools
Character counter
One count, measured against all seven networks’ limits at the same time.
Thread splitter
Turn a long piece of writing into a thread that fits, split at sentence boundaries.
X API cost calculator
What X actually charges to publish a post — and why a link costs twenty times more.
UTM builder
Build a tagged campaign URL without hand-editing a query string.
This is one check out of a product full of them
postfast runs this inside its composer, on every post, against every network you publish to. Join the waitlist for early access.