Compositor Review: The Free Photoshop Alternative for Mac Has a Project Format AI Can Edit Live

Daniel Carr, MSW

Sep 25

4 min read

Compositor is a new free image editor for Mac that describes itself as a Photoshop alternative, but its most unusual feature is not another brush, filter, or layer effect.

Compositor projects are stored as ordinary folders containing PNG layer images and a JSON manifest, which means scripts and AI coding agents can create or modify a project while Compositor is open.

The project appeared on GitHub on September 16, 2026 and has already accumulated more than 5,500 stars and 600 forks. Development has also been unusually fast. Compositor 1.3.2 was released on September 25, only hours after version 1.3.1, with continuing changes to text editing, filters, interface behavior, and project handling.

Compositor is already a substantial image editor

The application is not merely a demonstration of image layers. Compositor supports folders, masks, clipping masks, adjustment layers, Photoshop blend modes, nondestructive transforms, selections, painting tools, text, gradients, shapes, clone stamping, spot healing, Camera Raw controls, curves, levels, color grading, blur effects, noise, bloom, lens correction, and background removal.

It can import JPEG, PNG, HEIC, TIFF, SVG, camera RAW files, and Photoshop PSD and PSB documents. Some Photoshop structures remain editable after import, including folders, masks, blend modes, simple text, and basic vector shapes. More complicated vectors and unsupported text arrangements can be converted into pixels during import.

The interface also deliberately follows a Photoshop style workflow. Keyboard shortcuts can be remapped, multiple projects can remain open in tabs, and the layer model should be immediately recognizable to users accustomed to conventional desktop image editors.

The .comp project format changes what software can do with the editor

A Compositor project is not one opaque document. A file ending in .comp is actually a folder containing a manifest.json file and an images directory filled with PNG files representing individual layers.

The manifest describes the canvas dimensions, layer order, opacity, blend modes, transforms, masks, adjustment settings, and other document structure. A program that knows this format can create a layer by writing a PNG and adding the corresponding information to the manifest.

Compositor 1.3 and newer can watch an open project for those file changes. According to the project's documentation, the application normally reloads a modified project within roughly a third of a second after writing stops. The user can then select, repaint, transform, mask, or otherwise edit the newly created layers normally inside Compositor.

This produces a form of automation that does not depend on a proprietary plugin system. Claude Code, Codex, a local script, or another program capable of writing files can alter the same layered document that a person is editing through the graphical interface.

AI can build the document without controlling the mouse

Most attempts to connect AI agents with desktop creative software involve simulated mouse clicks, keyboard input, accessibility interfaces, or application specific automation APIs. Compositor's format allows a different approach.

An agent can read the documented project structure, create PNG layers, modify their placement and opacity in manifest.json, and write the project directly. Compositor then reloads the changed files and displays the result. The agent does not need to locate buttons visually or imitate a person operating the interface.

The documentation even proposes a workflow where an agent creates a scene incrementally, adding one or two layers at a time while the user watches the canvas update. Those layers remain ordinary Compositor layers afterward rather than becoming a flattened image generated somewhere else.

There are limitations. Reloading an externally modified project clears the current undo history, and Compositor will ask before replacing unsaved human edits. Invalid project data is ignored rather than partially loaded. The documentation also recommends writing new PNG files first and replacing the manifest last so the application never encounters a partially written document.

This could be more useful than an AI image generator inside the app

Embedding an image model into an editor usually gives the application one additional tool. An open project format gives outside software access to the structure of the document itself.

An agent could theoretically create a background layer, generate separate foreground elements, position them independently, construct masks, add adjustment layers, and leave every component available for manual editing. A script could also generate repetitive layouts, update hundreds of similar assets, or produce templates without operating Compositor's interface.

The distinction is architectural. The AI does not need to become part of Compositor, and Compositor does not need to know which automation tool produced the files. Anything capable of creating valid PNG files and JSON can participate in the workflow. That approach also avoids locking automation to a particular model provider. A Codex workflow today could be replaced by another agent later without changing the document format.

It is still a very young Photoshop alternative

Compositor has accumulated an impressive feature list quickly, but its GitHub issues show the consequences of that pace. Recent reports and requests concern text formatting, language support, SVG handling, Photoshop compatibility, interface behavior, and broader platform availability.

The current application requires macOS 26.5 or newer. Windows and Linux versions do not currently exist, and both have already been requested by users. The application is written as a native Mac program, so those ports would require considerably more work than producing another build of the existing project.

Version 1.3.2 also changes the project format enough that documents saved with it require Compositor 1.3.2 or newer to reopen. Anyone using the application for serious work should therefore pay attention to version compatibility while development remains this rapid.

Compositor is becoming more than a cheaper Photoshop substitute

Calling Compositor a free Photoshop alternative describes the visible product but misses the direction in which the project is developing. Its conventional editing tools make it usable as an image editor, while the transparent project structure allows other software to participate directly in the editing process.

That combination is unusual. A person can work visually, an agent can manipulate the same layered project through files, and neither workflow needs to replace the other.

For users who simply want Photoshop style editing without a subscription, Compositor is already worth watching. For developers and people experimenting with AI assisted creative workflows, the .comp format may be the more consequential feature.