gumcli

gumcli is a cross-platform .NET tool for working with Gum projects without the editor. It is the primary way an AI assistant acts on a Gum project and verifies its own work: machine-readable output on stdout, meaningful exit codes, fully headless. Full reference: https://docs.flatredball.com/gum/cli.

Install

dotnet tool install -g GumCli

The edit → validate → verify loop

After any change to a Gum project (by hand, by tool, or by an assistant), run this loop. Skipping validation is the most common way agent-authored UI breaks silently.

1. Generate code (project + codegen mode only)

gumcli codegen-init  MyProject.gumx     # once: writes code-gen settings
gumcli codegen       MyProject.gumx     # after any element edit: emits typed C#

Regenerate after editing elements so the generated classes match the XML. If you rename or delete an element, delete its stale generated .cs file before regenerating.

2. Validate — always

gumcli check MyProject.gumx            # human-readable
gumcli check MyProject.gumx --json     # machine-readable

check catches the mistakes that are easy to make and invisible otherwise — most importantly misspelled XML element names that Gum drops without error (see gum-file-format). Exit code 0 = clean, 1 = errors found, 2 = project could not be loaded / bad arguments. Branch on the exit code; do not parse prose. Run check after every hand edit before trusting the file.

3. Verify visually

Compiling is not proof the UI looks right. Render it and inspect:

gumcli screenshot MyProject.gumx ScreenOrComponentName --output out.png
gumcli svg        MyProject.gumx ScreenOrComponentName --output out.svg

Open the image to confirm layout matches intent. With a multimodal model, the assistant can look at the PNG directly.

Other commands

Command	Purpose
gumcli new <path> [--template forms|empty]	Scaffold a new project. forms (default) includes the built-in Forms controls.
gumcli fonts <project.gumx>	Generate missing bitmap font files (.fnt+.png). Windows-only.
gumcli pack <project.gumx>	Bundle a project into a single file.

Notes

• stdout is data, stderr is chatter. Consume results (--json, paths) from stdout; banners and progress go to stderr.
• Pair gumcli with the MCP documentation server so the assistant can look up a property while it drives the project. See https://docs.flatredball.com/gum/ai/gumcli-for-agents.