Mastodon character limit, media, alt text and polls
A Mastodon post holds 500 characters by default, but each server sets its own limit, and some allow thousands. Every link counts as 23 characters, and a content warning counts toward the limit too. A post can carry 4 images or one video, images up to 16 MB and video up to 99 MB. Here is every Mastodon limit, from Mastodon's source code and live servers.
Every number checked against its source on Nov 12, 2026.
Mastodon limits at a glance
| Limit | Mastodon allows | In PostDaily | Source |
|---|---|---|---|
| Post length | 500 characters by default; each server sets its own (mastodon.social 500, hachyderm.io 2,263) | Your server's own limit, read when you connect and at each health check; 500 if it can't be read | Mastodon docs: Instance (each server's own limits) |
| How it counts | Every link counts as 23 characters, a mention of someone on another server counts only @name, and an emoji is 1 | Counted the same way, except some emoji, such as flags, count as 2 or more | Mastodon source: status length validator |
| Content warning | Counts toward the post's limit, together with the text | Counted toward the limit, on every post in a chain | Mastodon source: status length validator |
| Media per post | 4 by default; up to 4 images, or one video or audio file on its own | Up to 4 images or 1 video, within your plan's media per post (4 on Free, 6 on Starter, 8 on Pro and 12 on Agency) | Mastodon source: posting a status |
| Image file | 16 MB by default; refused above 33,177,600 pixels (7680 × 4320); JPEG, PNG, GIF or WebP | 16 MB; larger photos are resized to 5,760 pixels on the long side before upload | Mastodon source: image size checks |
| GIF | Up to 1280 × 720 pixels; shown as a looping video | Not accepted (the media library doesn't store GIFs) | Mastodon source: image size checks |
| Video file | 99 MB by default; WebM, MP4, MOV or Ogg; up to 3840 × 2160 pixels and 120 frames a second | MP4, WebM or MOV up to 99 MB and 3840 × 2160, within your plan's per-file cap (25 MB on Free, 50 MB on Starter, 100 MB on Pro and 250 MB on Agency); frame rate not checked | Mastodon source: media attachments |
| Video length | No set length; a video Mastodon re-encodes keeps at most 36,000 frames (20 minutes at 30 frames a second) | — | Mastodon source: media attachments |
| Alt text | 10,000 characters on Mastodon 4.6 and later; 1,500 on older servers | 1,000 characters | Mastodon source: media attachments |
| Poll | 2 to 4 options of up to 50 characters, open 5 minutes to 1 month; not in a post with media | Not offered | Mastodon source: poll options validator |
| Visibility | Public, unlisted (Mastodon now calls it quiet public), followers only, or private mention | Public, unlisted or followers only | Mastodon docs: posting a status |
| Scheduled posts | Mastodon's own scheduling needs a post at least 5 minutes ahead, with at most 25 a day and 300 waiting | Doesn't apply: PostDaily publishes each post at its time instead of handing it to the server early | Mastodon source: scheduled statuses |
| Threads | No limit on how many replies a thread has | A chain of up to 25 posts, each a reply to the one before | Mastodon docs: posting a status |
| Rate limits | 300 requests every 5 minutes per account, and 30 media uploads every 30 minutes | — | Mastodon docs: rate limits |
500 is only the default
Mastodon is thousands of servers, and each one sets its own limits. 500 characters is what Mastodon ships with, and the large general servers such as mastodon.social keep it, but others raise it: hachyderm.io allows 2,263. Each server publishes its limits, so an app can read them instead of guessing.
PostDaily reads your server's limit when you connect the account, and again at each health check, so the counter uses your server's number. If it can't read one, it uses 500. Try a server's limits with the free Mastodon character counter.
Links count 23, and the content warning counts too
Mastodon counts every link as 23 characters, however long it is, so a long address doesn't eat the post. A full stop or comma right after a link is not part of it, and counts on its own. A mention of someone on another server, such as @name@example.social, counts only the @name part.
A content warning shares the limit with the text: on a 500-character server, a 20-character warning leaves 480 for the post. PostDaily counts it the same way on every post in a chain, so a post that fits in PostDaily fits on the server. More on the Mastodon character limit.
Images, video and pixels
By default a post holds 4 images, or one video on its own. Images can be up to 16 MB, but Mastodon refuses one above 33,177,600 pixels (7680 by 4320), whatever the file size, so PostDaily resizes a larger photo to 5,760 pixels on its long side before uploading it. Mastodon shrinks stored photos to 3840 by 2160 anyway, so nothing visible is lost.
Video can be up to 99 MB and 3840 by 2160 pixels; PostDaily checks both, and a 4K cinema or 8K video is stopped before the upload. Mastodon also refuses video above 120 frames a second, which PostDaily doesn't check. Uploads through PostDaily are also capped per file by plan: 25 MB on Free, 50 MB on Starter, 100 MB on Pro and 250 MB on Agency.
Where Mastodon's own docs disagree
Mastodon's posting guide says poll options are 25 characters; the source code and live servers say 50. Its guide to the Instance API shows an alt text limit of 1,500 in its example, which is the old value; servers on 4.6 or later allow 10,000. Mastodon 5.0, already running on mastodon.social, has also turned off HEIC and AVIF images for now. This page follows the source code and what live servers report.
What PostDaily checks, and what it doesn't
Before a post is scheduled, PostDaily checks the length against your server's limit with links, mentions and the content warning counted Mastodon's way, the number of images, file sizes and pixel sizes. Each post in a chain is checked on its own. It doesn't offer polls, quote posts or private mentions. Mastodon allows 30 media uploads every 30 minutes, so a long chain with images in every post is better split across two schedules. Schedule Mastodon posts and threads.
Common questions
- What is the Mastodon character limit?
- 500 characters by default, but each server sets its own, and some allow several thousand. Every link counts as 23.
- Does the content warning count toward the Mastodon character limit?
- Yes. Mastodon adds the content warning to the text and checks the total against the server's limit.
- How many images can you post on Mastodon?
- 4 images per post by default, or one video or audio file on its own.
- What is the Mastodon video size limit?
- 99 MB by default, up to 3840 × 2160 pixels and 120 frames a second. Servers can change it.
- How long can Mastodon alt text be?
- 10,000 characters on Mastodon 4.6 and later, and 1,500 on older servers.
Sources
- Mastodon docs: Instance (each server's own limits)
- Mastodon source: status length validator
- Mastodon source: posting a status
- Mastodon source: image size checks
- Mastodon source: media attachments
- Mastodon source: poll options validator
- Mastodon docs: posting a status
- Mastodon source: scheduled statuses
- Mastodon docs: rate limits