Mastodon Specifications

Post Image

Dimensions	1280 × 720 px recommended
Max File Size	8 MB (mastodon.social default; varies by instance)
File Formats	JPG, PNG, GIF, WEBP, HEIC
Notes	Up to 4 images per post; each instance may set different limits

Profile Photo

Dimensions	400 × 400 px recommended
Max File Size	2 MB
File Formats	JPG, PNG, GIF
Notes	Animated GIFs supported for avatar; displayed as a circle

Profile Header Banner

Dimensions	1500 × 500 px
Aspect Ratio	3:1
Max File Size	2 MB
File Formats	JPG, PNG, GIF

Post Video

Max File Size	40 MB (mastodon.social; varies by instance)
File Formats	MP4, MOV, WEBM, M4V
Resolution	Up to 1920 × 1080 px
Notes	H.264 + AAC recommended; instance admins set upload limits

Animated GIF

Max File Size	8 MB
File Formats	GIF
Notes	Plays silently in-feed; click to open with sound if attached video

Post (Toot)

Character Limit	500 characters
Notes	Default on mastodon.social; instance admins can increase this limit

Content Warning / Subject

Character Limit	500 characters
Notes	Optional CW hides post body until clicked

Display Name

Character Limit	30 characters

Bio

Character Limit	500 characters
Notes	Supports HTML-style formatting; links in bio are auto-verified

Profile Metadata Fields

Character Limit	4 fields fields
Notes	Each field label up to 255 characters, value up to 255 characters

Profile Photo

Dimensions	400 × 400 px
Max File Size	2 MB
File Formats	JPG, PNG, GIF
Notes	Displayed as a circle

Header Banner

Dimensions	1500 × 500 px
Aspect Ratio	3:1
Max File Size	2 MB
File Formats	JPG, PNG, GIF

Hashtag

Character Limit	No set limit characters
Notes	Hashtags are the primary discovery mechanism; no ads on the federated network

Poll Options

Character Limit	4 options
Notes	Each option up to 50 characters; polls can run 5 minutes to 7 days