config-set

Config set

Persist an engine-wide configuration value. The single key the engine reads today is diff.tool — the command /skill-engine:review prints when surfacing how to inspect a proposed-vs-live diff. The default value is git diff --no-index --color; users with a preferred diff tool override it once and the choice persists across sessions.

Argument shape

/skill-engine:config-set <key> "<value>"

Example invocations:

/skill-engine:config-set diff.tool "delta"
/skill-engine:config-set diff.tool "git diff --no-index --color"
/skill-engine:config-set diff.tool "code --diff"

The <value> is taken verbatim; quote it so shell-splitting does not eat embedded spaces. The engine does not validate that the configured command exists on the user's PATH — that is the user's responsibility. A misconfigured command surfaces as a runtime failure when /skill-engine:review prints it and the user runs it.

Resolution of the config file

The config file lives at $CLAUDE_PLUGIN_DATA/config.json. The directory is created if absent.

When $CLAUDE_PLUGIN_DATA is unset, surface:

$CLAUDE_PLUGIN_DATA is unset. The engine's plugin-data tree is not reachable from this shell. Run the skill from a Claude Code session where the plugin is installed, or set $CLAUDE_PLUGIN_DATA to the engine's plugin-data directory.

Exit non-zero. Do not write a config file to a fallback location — the engine's other surfaces (/skill-engine:review) key off $CLAUDE_PLUGIN_DATA, and writing to a different path would create a config that the readers never find.

The write

Read the existing config.json (or initialize an empty object if absent). Merge the new key/value into it, preserving any other keys present. Write back with schema_version: 1 if not already set.

Example file shape after /skill-engine:config-set diff.tool "delta":

{
  "schema_version": 1,
  "diff.tool": "delta"
}

The flat key shape (diff.tool as one string, not nested) keeps the file shallow and matches the argument the user typed. Future keys (diff.binary, cache.location, etc.) follow the same shape.