Configuration

File location

On macOS, the released code resolves dirs::config_dir() and appends molt/config.toml:

~/Library/Application Support/molt/config.toml

Molt creates the parent directory and a default file when the file does not exist.

Complete default configuration

config.toml

[python]
# Path to the Python interpreter to use for all kernels.
# Supports absolute paths or names resolvable on PATH.
# Default: "python3"
interpreter = "python3"

[app]
# Launch Molt automatically at macOS login.
auto_launch = false

# Number of tabs. Currently fixed at 4; reserved for future use.
tab_count = 4

# Enable native macOS glass/vibrancy window effects.
native_effects = true

Field reference

python.interpreter

Property	Value
Type	String
Default	python3
Accepted form	Absolute executable path or command resolvable through the app process’s PATH
Validation	Executes the configured value with --version during app startup
Runtime application	Captured when the Rust KernelManager is created; requires a full app relaunch after change
Scope	One interpreter for all tabs

A failed validation produces a warning stored in application state and shown as a banner. The warning text is not recalculated after Settings is saved; relaunch is required.

app.auto_launch

Property	Value
Type	Boolean
Default	false
Parsed and saved	Yes
Applied to macOS login items	No, not in this release

Treat this as a reserved field. Configure a login item through macOS itself when needed.

app.tab_count

Property	Value
Type	Unsigned 8-bit integer in Rust
Default	4
Parsed and saved	Yes
Applied by frontend	No; frontend constructs indices 0–3 explicitly

Keep the value at 4.

app.native_effects

Property	Value
Type	Boolean
Default	true
Live preview	Yes, through set_native_effects
Persisted	Only after the settings form is saved
Enabled behavior	Apply macOS HudWindow vibrancy and translucent CSS surfaces
Disabled behavior	Clear vibrancy and apply opaque CSS surfaces without decorative shadows

Missing or invalid data

Serde defaults fill omitted sections and fields. Examples:

• An omitted [app] section receives all app defaults.
• An omitted native_effects field receives true.
• A legacy theme field is ignored.

If the entire TOML cannot be read or parsed, load_config logs a warning and returns defaults. The source file is not automatically repaired until Settings is saved.

Save behavior

Saving Settings rewrites the entire file in Molt’s canonical order and comment format. Unknown fields are dropped because the form serializes only the current AppConfig structure.

Quit Molt before editing TOML manually. The app reads configuration during startup and at a few explicit operations; it does not watch the file for changes.