Check the media against the platform before you fill the calendar

The expensive way to discover a platform limit is at publication time, when the work is finished, the slot is booked and the only available fix is to cut something. The cheap way is to check the limits while the piece is still an outline, because they are published, they are specific, and they disagree with each other in ways no general rule can absorb.

The tables below are generated from the dataset this site keeps for the launch cohort, which is itself derived from the connector registry. That means these numbers cannot quietly drift away from the ones the product uses, and a platform with no adapter shows as unavailable rather than as a zero.

The third column is the one that surprises people. A caption that fits by one measure can overflow by another, because a family emoji, an accented character and a Japanese sentence are counted differently depending on which unit the platform chose. A preflight that counts with the wrong unit is a preflight that passes work the platform will refuse.

Read that table as a planning constraint rather than as an export setting. A destination with no images is not a place a carousel can be adapted into. A destination with no recorded alt text ceiling is a place where meaning carried by words inside a picture has to move into the visible caption, or it is lost to anybody using a screen reader.

1. 01Decide the shape per destination first: text, image with caption, several images, video, or a link. Everything else follows from that.
2. 02Count the body with the unit the destination actually uses, and count the link the way that destination charges for it.
3. 03Check the file against the recorded size and duration ceilings before rendering the final version, not after.
4. 04Write the alt text where the destination has a field for it, and move the meaning into the caption where it does not.
5. 05Record the date you checked each limit. A number without a date is a rumour.

Steps one and two remove most publication time failures on their own. Step five is what keeps the whole sheet honest a year later, when the platform has quietly changed a ceiling and nobody noticed because the old number still looked authoritative.

Video adds a state that text never has. Several platforms accept an upload, take it away to process, and only then make it publishable, so a queue that treats an accepted upload as a finished post will publish nothing at the moment it promised.

Plan the processing window into the schedule rather than into the retry logic. A video that has to be live at nine should be uploaded long enough before nine that a slow encode is an inconvenience rather than a missed slot.

See the full limits and the sources per platform