Gum gum-tool-output

Reference guide for Gum's Output tab system. Load this when working on the Output tab, IOutputManager, MainOutputViewModel, GuiCommands.PrintOutput, or adding output/error messages to the tool.

install

source · Clone the upstream repo

git clone https://github.com/vchelaru/Gum

Claude Code · Install into ~/.claude/skills/

T=$(mktemp -d) && git clone --depth=1 https://github.com/vchelaru/Gum "$T" && mkdir -p ~/.claude/skills && cp -r "$T/.claude/skills/gum-tool-output" ~/.claude/skills/vchelaru-gum-gum-tool-output && rm -rf "$T"

manifest: .claude/skills/gum-tool-output/SKILL.md

Gum Tool Output System Reference

Architecture

IOutputManager

(

Gum/Managers/MainOutputViewModel.cs

) — interface with two methods:

```
AddOutput(string)
```
— appends a timestamped line
```
AddError(string)
```
— appends a timestamped line prefixed with
```
"ERROR:  "
```
(two spaces)

MainOutputViewModel

— implements

IOutputManager

. Stores all output as a single

OutputText

string (not a list). Registered as a singleton in DI, aliased as both

MainOutputViewModel

and

IOutputManager

MainOutputPlugin

—

PriorityPlugin

that creates the Output tab at

TabLocation.RightBottom

How to Write Output

Inject

IOutputManager

and call

AddOutput

AddError

directly — this is the standard approach. Callers must already be on the UI thread.

IGuiCommands.PrintOutput

is a thin wrapper around

AddOutput

that marshals to the UI dispatcher — use this when calling from a background thread. There is no
PrintError
equivalent in

IGuiCommands

; callers needing

AddError

from a background thread must dispatch manually.

Non-Obvious Behaviors

Buffer cap:
```
OutputText
```
is capped at 50,000 chars. When exceeded, it is trimmed to the last 25,000 chars — oldest output is silently discarded.
No dispatcher in
IOutputManager
:
```
AddOutput
```
/
```
AddError
```
write directly to the
```
OutputText
```
property with no thread marshaling. Calling from a background thread will throw.
Auto-scroll: The
```
TextBox
```
in the view uses
```
TextBoxAutoScroll.AutoScrollToEnd="True"
```
— new output scrolls into view automatically.

Key Files

File	Purpose
`Gum/Managers/MainOutputViewModel.cs`	`IOutputManager` interface + `MainOutputViewModel` implementation
`Gum/Commands/GuiCommands.cs`	`PrintOutput` — dispatcher-safe wrapper
`Gum/Commands/IGuiCommands.cs`	`PrintOutput` declaration
`Gum/Plugins/InternalPlugins/Output/MainOutputPlugin.cs`	Registers the Output tab
`Gum/Plugins/InternalPlugins/Output/MainOutputPluginView.xaml`	Output tab view (TextBox + clear button)
`Gum/Services/Builder.cs`	DI registration of `MainOutputViewModel` as `IOutputManager`