File types and limits

Uploading, previewing, and processing are separate. A successful upload does not guarantee that Atoms can display a preview or that an agent can read and use everything in the file.

Chat attachment and folder limits

Upload location or action	Limit	What to expect
Attach files, including videos, on the home page or in project chat	100 MB per file	Files over the limit are skipped. Other valid files can continue uploading.
Drag a folder into the home-page or project-chat upload area	500 files and 10 nested levels per folder drop	If either limit is exceeded, the entire folder drop is cancelled. Reduce the file count or simplify the folder structure, then try again.

The folder-drop limit is not a general attachment limit per message. Each file in a folder is also subject to the chat per-file size limit. These rules describe the chat upload area, not a separate Files-panel upload or files submitted by visitors to your published app.

Sizes use the units shown in Atoms. For these checks, 1 MB equals 1,048,576 bytes. A file exactly at a stated maximum is within the size limit; the DOCX preview exception is explained below.

Video uploads

Video files attached on the home page or in project chat use the same 100 MB per-file limit. If a video is larger than 100 MB, it won’t upload. Reduce the file size, then try again.

Built-in video previews support MP4, WebM, and MOV, subject to browser and encoding compatibility. Uploading within the size limit does not guarantee that a video’s duration, resolution, or encoding is supported for playback or AI processing. This attachment limit does not establish the limits for separate video-editor imports or model-specific reference videos.

File types you can preview

The following formats have built-in preview support. This is a preview reference, not a complete list of formats accepted for upload or supported for AI processing.

File category	Preview formats	Notes
Images	.jpg, .jpeg, .png, .gif, .bmp, .webp, .svg, .avif, .ico	Image-upload tools can have a narrower format list; see the additional limits below.
Documents	.pdf, .docx	DOCX preview requires a file smaller than 10 MB. A DOCX file at or above that size may upload successfully but cannot use the built-in DOCX preview.
Spreadsheets and tabular data	.xlsx, .csv	Preview support does not guarantee that every spreadsheet feature is reproduced.
Text, Markdown, code, and configuration	.txt, .md, and common source/configuration formats, including .js, .ts, .jsx, .tsx, .vue, .html, .css, .py, .json, .yaml, .xml, .sql, and .sh	The code/configuration extensions shown are examples, not an exhaustive list.
Notebooks and diagrams	.ipynb, .mmd, .mermaid	Notebook and Mermaid preview formats.
Audio	.mp3, .wav, .ogg, .aac, .flac	Playback also depends on browser and encoding support.
Video	.mp4, .webm, .mov	Playback also depends on browser and encoding support.

Files without a built-in preview

Some file types can be uploaded but cannot be previewed directly, including:

• Archives: ZIP, RAR, 7Z, TAR
• Office files: DOC, XLS, PPT, PPTX
• Document formats: EPUB, RTF
• Design files: PSD, AI, FIG, Sketch
• Images and media: HEIC, HEIF, TIFF, AVI, MKV, M4A

A missing preview does not, by itself, mean the upload failed.

If an uploaded file has no preview, download it and open it in a compatible application. Folders do not have an individual file preview; open a file inside the folder instead.

Additional image and storage upload limits

Use the limit for the specific tool you are using. A file that fits within the chat limit can still be too large for one of these image controls.

Upload location	Maximum per image	Formats
Design → image library → Upload	4 MB	JPEG (.jpg, .jpeg), PNG, GIF, BMP, TIFF (.tif, .tiff), WebP
Design → Visual Editor → select an image → image tool → Upload	5 MB	The file picker offers PNG, JPG/JPEG, GIF, BMP, and WebP.
App logo	5 MB	PNG, JPEG
Social preview image	5 MB	PNG, JPEG, WebP
Profile picture	2 MB	PNG, JPEG
Workspace image — desktop	5 MB	PNG, JPEG, WebP
Workspace image — mobile	5 MB	PNG, JPEG, WebP, SVG
AppWorld publishing cover	3 MB	An image file recognized as an image by your browser.

The Design image-library uploader accepts TIFF, but it is not included in the general file-preview image formats above.

Atoms Cloud storage: Uploading a file through the Cloud storage panel has a 100 MB per-file limit. This is separate from chat attachments and from your total storage allowance. It does not establish a limit for upload features you build into a published app.

Other file-handling behavior

Unreadable images. Chat uploads check common bitmap images for readability. If an image cannot be read, it is skipped and you are prompted to provide a valid image. Open the original locally and export a fresh copy before trying again.

Long pasted text. Text pasted into the chat editor can become a TXT attachment when it reaches 50 lines or 2,000 characters. This is an automatic attachment-conversion threshold, not a maximum document length.

Using files with an agent. A preview confirms only that the file can be displayed. It does not establish support for transcribing audio, extracting archives, reading scanned pages, or interpreting every element of a complex document.

If a file is rejected or cannot be used

What happens	What to do
The file is too large	Check the limit for that upload location. Compress or export a smaller copy, or split the content into smaller files where practical. Keep the original.
A folder drop exceeds the file-count or nesting limit	Split the folder into smaller groups or reduce nested subfolders, then retry. The rejected folder drop does not upload partially.
An image tool rejects the format	Export the image in one of that tool’s listed formats. Renaming the file extension does not convert the file.
Atoms reports an invalid or unreadable image	Check that the image opens locally. Re-export it from an image application or obtain a new copy, then upload again.
“File uploaded, but preview is unavailable”	The upload may have succeeded. Check the preview formats and DOCX preview size restriction above, or download the file and open it locally.
An audio or video preview will not play	Check local playback and browser compatibility. If needed, re-export using a browser-compatible encoding and one of the listed preview formats.
The agent cannot use an uploaded file as expected	Specify the content you want it to use. Where possible, provide the relevant text or a simpler export instead of relying on the original file’s complex layout.
The error refers to storage capacity	Check the relevant storage usage and allowance. A total-capacity issue is different from exceeding the size limit for one file.

If the issue continues, contact Atoms Support at [email protected]. Include the upload location, file extension, file size, and exact error message. Avoid sharing sensitive file contents unless necessary.

Related help

• Input chat — using the chat input and attachments.
• Code and files — viewing, editing, and downloading project code.
• App storage — working with stored app files and storage access.