Environment variables

Environment variables pass settings to a running program. Some let you change how discerndiscernA tool that lets you hand real work to coding agents and still decide what joins your project. starts; others give your project scriptsProject scriptA procedure your project provides for its agents and maintainers to run. information such as the current worktreeWorktreeA separate copy of your project, on its own branch, where one task's work happens. 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

You can set these when you run the install script, to change what it downloads and where it puts discern.

Variable	What it does
`DISCERN_REPO`	The GitHub repository, as `owner/repo`, whose releases the install script downloads. Default: `discern-sh/discern`.
`DISCERN_VERSION`	The release the install script downloads, with or without a leading `v`. Default: `latest`.
`DISCERN_BIN_DIR`	The folder the install script puts discern in, created if it doesn't exist. Without it, the script uses a writable `/usr/local/bin` on macOS, and otherwise `~/.local/bin`, then a writable `/usr/local/bin`.

Runtime overrides

You can set these to change how discern behaves, for one command or for your whole session.

Variable What it does

DISCERN_TRUNK Use a different trunkTrunkYour project's shared branch, usually main, where finished changes land. than [repository].trunk while it's set; an empty value is ignored. discern also sets it for each project script, to the trunk in use.

DISCERN_NO_ATTRIBUTION Set it to any non-empty value to leave discern's name off what it writes. Generated-fileGenerated fileA file discern builds for your coding agents: an agent file or a skill folder. markers drop discern's name and web address, commits discern makes drop its co-author line, and Proof notesProof noteA copy of a landed change's Proof, stored with its commit in Git. use your Git identity instead of discern's. Keep it set the same way for every command, or discern upgrade --check reports the markers as out of date.

Variable	What it does
`DISCERN_TRUNK`	Use a different trunkTrunkYour project's shared branch, usually `main`, where finished changes land. than `[repository].trunk` while it's set; an empty value is ignored. discern also sets it for each project script, to the trunk in use.
`DISCERN_NO_ATTRIBUTION`	Set it to any non-empty value to leave discern's name off what it writes. Generated-fileGenerated fileA file discern builds for your coding agents: an agent file or a skill folder. markers drop discern's name and web address, commits discern makes drop its co-author line, and Proof notesProof noteA copy of a landed change's Proof, stored with its commit in Git. use your Git identity instead of discern's. Keep it set the same way for every command, or `discern upgrade --check` reports the markers as out of date.

Worktree identity

You can set these to replace the names discern works out for a worktree.

Variable	What it does
`DISCERN_PROJECT_SLUG`	Use this slug instead of `[project].slug` in a worktree's site, database, and resource names. discern converts it to lowercase and turns other characters into dashes; the `@project_slug@` token keeps the configured slug.
`DISCERN_WORKTREE_BRANCH_PREFIX`	Use this prefix instead of `[repository].branch_prefix` for worktree branch names. An empty value means no prefix.
`DISCERN_WORKTREE_ID`	Give a worktree a chosen id, which its port, site, database, and resource names follow. Set it in the environment, where it applies to the worktree the command runs in, or on a line in that worktree's env files. It starts with a letter or digit and continues with letters, digits, dots, dashes, or underscores, up to 81 characters; discern converts it to lowercase and turns dots and underscores into dashes.

Project Scripts

discern sets these for a project script each time it runs one, from discern scripts or the deskDeskThe interactive view that opens when you run discern in your main checkout.. It removes any other DISCERN_* variables from the script's environment.

Variable	What it does
`DISCERN_ROOT`	Absolute path of the project root.
`DISCERN_TOML`	Absolute path of the `discern.toml` in use.
`DISCERN_SCRIPTS_DIR`	Absolute path of the project scripts folder, `[scripts].dir`.

Checkpoint commands

discern sets these for a checkpointCheckpointA review question your project asks your agent whenever a certain kind of change happens.'s when command while it runs.

Variable	What it does
`DISCERN_CHECKPOINT_INPUT`	Absolute path of a JSON file that describes the change for the checkpoint's `when` command. It holds facts about the changed files, but not their contents, in the versioned format the checkpoint `when` protocol describes. The file exists only while the command runs.

Worktree environment

discern gives these to a worktree's resource commands or writes them into its env files, as each entry describes. It only writes into env files that already exist.

Variable	What it does
`DISCERN_WORKTREE_PORT`	The worktree's stable development port. discern writes it into the worktree's env file when `[worktree].export_port = true`; `discern identity --port` prints it either way.
`DISCERN_WORKTREE`	The worktree's resource handle, a stable name made from the project slug and worktree id. discern gives it to every resource command, and writes it into the env files when a resource has a `create` or `destroy` command.
`DISCERN_RESOURCE_<NAME>`	The stable name of one declared resource. Each resource command gets its own resource's variable, and discern writes them into the env files alongside `DISCERN_WORKTREE`. `<NAME>` is the resource's name in uppercase, with each run of other characters turned into one underscore and any at the ends removed.

Experimental features

You can set these to try an experiment. Their names and behavior may change in any release.

Variable	What it does
`DISCERN_EXPERIMENTAL_MCP_PRELOAD`	Set it to `1` to have coding agents that support it load discern's MCP tools at startup instead of on first use. discern applies it whenever it writes agents' MCP settings, as `discern refresh` does. Use the same setting when you run `discern done`, which checks those settings against what a refresh would write.
`DISCERN_EXPERIMENTAL_AWAIT_CALL_SECONDS`	Limit each await to this many whole seconds; it can only shorten the usual limit. It applies to every agent `discern_await` call and to `discern await` without `--timeout`. An explicit `--timeout` on the command line still applies in full.