Environment variables

Environment variables pass settings to a running program. Some let you change how discerndiscernA tool that installs and runs an agent development practice in a project. starts; others give your project scripts information such as the current worktreeWorktreeA separate working copy and branch for one effort. or its assigned port. This page lists the supported DISCERN_* variables by purpose.

Find the variable name below to see who sets it, who reads it, and its default where one exists. Setting a variable affects the current process unless its entry says discern exports or writes it. For lasting project settings, use discern.toml.

Installation

Inputs read by the POSIX installerInstallerThe commands that set up and maintain discern in a project..

Variable	What it does
`DISCERN_REPO`	GitHub release repository the installer downloads from. Defaults to `discern-sh/discern`.
`DISCERN_VERSION`	Release version the installer downloads, with or without a leading `v`. Defaults to `latest`.
`DISCERN_BIN_DIR`	Install directory. Overrides the installer's automatic destination selection.

Runtime overrides

Per-process overrides for discern's runtime behavior.

Variable	What it does
`DISCERN_TRUNK`	Overrides `[repository].trunk` for the current process. Project Scripts receive the resolved trunkTrunkThe shared branch that accepted work joins, usually `main`. in the same variable.
`DISCERN_NO_ATTRIBUTION`	Uses source-only generated-file markers and omits the discern co-author trailer from commits discern composes when set to a non-empty value.

Worktree identity

Inputs that override the identity derived for a worktree.

Variable	What it does
`DISCERN_PROJECT_SLUG`	Overrides `[project].slug` when discern derives worktree identities.
`DISCERN_WORKTREE_BRANCH_PREFIX`	Overrides `[repository].branch_prefix` when discern derives worktree branch names.
`DISCERN_WORKTREE_ID`	Sets an explicit worktree id in the process or a configured env file. Accepts letters, numbers, dots, dashes, and underscores.

Project Scripts

Values discern exports before running a Project ScriptProject scriptA runnable procedure the project supplies for its agents and maintainers..

Variable	What it does
`DISCERN_ROOT`	Absolute project root exported to a Project Script.
`DISCERN_TOML`	Absolute path to the active `discern.toml` exported to a Project Script.
`DISCERN_SCRIPTS_DIR`	Absolute configured Project Scripts directory exported to a Project Script.

Checkpoint commands

Structured inputs exported to checkpointCheckpointA review question presented when a relevant kind of change occurs. when commands.

Variable	What it does
`DISCERN_CHECKPOINT_INPUT`	Absolute path to the versioned JSON facts without raw file content for the current checkpoint `when` command. See the checkpoint `when` protocol. The file exists only while that command runs.

Worktree environment

Identity values passed to resource commands or written to configured worktree env files.

Variable	What it does
`DISCERN_WORKTREE_PORT`	Deterministic development port written to a configured worktree env file when `[worktree].export_port = true`.
`DISCERN_WORKTREE`	Generic worktree handle supplied to resource commands and written to configured env files when resources are declared.
`DISCERN_RESOURCE_<NAME>`	Stable handle for one declared resource. `<NAME>` is the resource name uppercased with non-alphanumeric runs replaced by underscores.

Experimental features

User-facing controls for experiments whose names and behavior remain subject to change.

Variable	What it does
`DISCERN_EXPERIMENTAL_MCP_PRELOAD`	Requests eager discern MCP loading in supported provider integrations when set to `1`.
`DISCERN_EXPERIMENTAL_AWAIT_CALL_SECONDS`	Sets a positive whole-number cap for one experimental automatic await call.