File types and limits
Check the size and format requirements before adding files to Atoms. The limit depends on where you upload: chat attachments, Design images, app branding, and profile images have different rules.
Check the size and format requirements before adding files to Atoms. The limit depends on where you upload: chat attachments, Design images, app branding, and profile images have different rules.
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.