Make every image Bluesky-ready.

Why check your images before posting to Bluesky?

Bluesky allows up to four images per post, and each image file can be at most 2,000,000 bytes (about 2 MB). Photos straight from a phone or camera often exceed that, and the limit is about file size, not how large the picture looks on screen. Checking first means you find out before you are in the middle of a post, and you can see exactly which images need attention.

File size, dimensions and format together decide how an upload behaves. The checker reports all three for every image, and only touches the ones that are over the limit. For the wider picture on why uploads can end up soft, read why photos look blurry on social media.

Bluesky's current image limits

These limits come from Bluesky's own published schemas (the lexicons that define what a post or profile record may contain). They describe what the schema accepts. They do not describe how any Bluesky app displays or re-processes an image afterwards.

• Post imagesUp to 4 images per post. Each file can be up to 2,000,000 bytes (about 2 MB).
• Link-card preview imageThe thumbnail of a link card can be up to 1,000,000 bytes (about 1 MB).
• Profile picture (avatar)Up to 1,000,000 bytes. PNG or JPEG only.
• Profile bannerUp to 1,000,000 bytes. PNG or JPEG only.

The schema sets file-size limits and accepted types. It does not set a width or height limit for any of these. The 3,840-pixel longest edge this tool applies when it prepares an image is SkyyCast's own setting, not a Bluesky requirement. The schema also notes that the post-image limit was formerly 1 MB, so older guides that still quote 1 MB for post images are out of date.

Last verified 30 September 2026 against Bluesky's official lexicon files in its public atproto repository on GitHub: app.bsky.embed.images, app.bsky.embed.external and app.bsky.actor.profile. Limits can change, so check the source if this date is old.

What this checker covers. It checks and prepares images for posts against the 2,000,000-byte post-image limit. It does not prepare avatars, banners or link-card previews, which have a smaller 1,000,000-byte limit, and because avatars and banners accept only PNG or JPEG, a WebP copy prepared here should not be used for them. For avatar and banner design advice, see how to optimize your Bluesky profile; this page does not recommend pixel dimensions for them because the schema does not specify any.

Why an image can fail to upload

• The file is over the size limit. The limit is on file size in bytes, not on how large the picture looks. A high-resolution phone photo or a detailed PNG can easily run to several megabytes.
• There are more than four images. A post can carry at most four.
• An avatar or banner is over 1,000,000 bytes, or is not a PNG or JPEG.
• A link-card preview image is over 1,000,000 bytes.

How an individual Bluesky app reacts to an oversized file (an error, automatic shrinking, or something else) is not defined by the schema and is not covered here. The safest approach is to check the file before you post.

How it works

1. 1CheckAdd up to four images and see each one's size, dimensions and format.
2. 2PrepareOversized images are re-encoded here, lowering quality first and resizing only if needed.
3. 3DownloadSave the prepared copy. Your original file is never changed.
4. 4PostAttach the image in Bluesky, or in the SkyyCast composer.

Privacy first

Your images are read and processed by your own browser. They are not uploaded to SkyyCast, stored, or sent to any other service, and no account is needed. Closing or reloading the page discards everything.

Preparing an image re-encodes it, which also drops embedded metadata such as camera details and GPS location from the prepared copy. Images that are already within the limit are left exactly as they are.

Practical tips for Bluesky images

• Keep your original file and post the prepared copy. This tool never changes the original.
• If a file is too big and you are preparing it yourself, reduce the pixel dimensions first and lower the JPEG quality second. Fewer pixels usually saves more bytes than lower quality. This is general image practice, not a Bluesky rule.
• Add a description to every image that carries meaning. See how to add alt text on Bluesky.

More free Bluesky tools

See all free Bluesky tools. Checking a whole draft? The Bluesky Post Validator checks a post's length against Bluesky's official limits, along with its images and alt text, in your browser. Uploading a video? The Bluesky Video Upload Checker checks its size, duration and format before you upload it.

About this tool

SkyyCast is an independent third-party service. It is not affiliated with, endorsed by or sponsored by Bluesky. The name “Bluesky” is used only to describe which service the tool prepares images for.