Environment variables

What it is

The environment variables that Loomcoding reads, with their default and their effect. It also lists the names that you choose yourself, such as the variable that holds a provider key, and the ones that herdr sets.

What it is for

• Running Loom with a separate profile, for tests or for a clean start.
• Turning on the log file, or turning off the output filter.
• Finding where a provider key is read from.

How

1. Set the variable in the shell before you start loom, or in the project .env file for provider keys.
2. Use the name exactly as written here. Names are case-sensitive.
3. Restart Loom after a change to a variable that is read at start. The table says when a variable is read.

Example

$env:LOOMCODING_HOME = "<temp folder>"
$env:RUST_LOG = "odd=info"
loom

This starts Loom with a separate profile, and writes the ODD events to the log file in logs/ of that profile.

Loom variables

Variable	Default	What it does
LOOMCODING_HOME	the system home folder	Root of the profile. Loom keeps its files in <value>/.loomcoding/. Use a temporary folder to run with a separate profile.
RUST_LOG	not set	When set and not empty, Loom writes a log file in logs/ of the profile. The value is a filter, for example odd=info. The file is rotated at 5 MiB.
LOOMCODING_NO_FILTER	not set	1 turns off the output filter for the whole process, even if [output_filter] enabled is true.
LOOMCODING_MAX_TOOL_CALLS_PER_RESPONSE	128	Maximum number of tool calls in one model response. Only a positive whole number is used; other values are ignored.
LOOMCODING_MAX_TOOL_CALLS_PER_TURN	256	Maximum number of tool calls in one turn. Same rule as above.
LOOMCODING_PROMPT_CACHE	not set	0, off or false turns prompt caching off in the Anthropic adapter. Any other value turns it on. When not set, [provider] prompt_cache decides, and the default is on.
LOOMCODING_PROGRAMMATIC_TOOL_CALLING	off	1, true or yes enables the programmatic tool-calling path of the agent loop. Any other value keeps it off.
LOOMCODING_NO_CLIPBOARD	not set	When set, to any value, Loom does not read images from the clipboard. Pasting text still works.
NO_COLOR	not set	When set, to any value, the braille mascot and the logo effects are turned off.
USERPROFILE, HOME	the system values	Used only to find the model catalog cache, models-dev.json. LOOMCODING_HOME does not move this file.

Provider keys and credentials

The name of a provider key variable is the value of api_key_env in loomcoding.toml or in providers.toml. You choose the name. These names appear by default in the files and in the settings screen:

Name	Where it appears by default
OPENROUTER_API_KEY	The fallback project file, used when providers.toml cannot be used.
STRATA_API_KEY	The strata entry of providers.toml.
ANTHROPIC_API_KEY, OPENAI_API_KEY, GEMINI_API_KEY	The provider presets of the settings screen.

Loom looks for a key in this order, and uses the first one that is not empty:

1. The process environment, under the name in api_key_env.
2. The .env file in the project root, under the same name.
3. The operating system credential store, under the same name.

For a local address (localhost or a loopback IP) with no key, Loom uses a placeholder key, so a local server that needs no key works without one. Loom does not write keys to any file.

Variables you name yourself

Setting	What the variable holds
api_key_env in [provider] or in providers.toml	The provider key. See the previous section.
env in [a2a.serve.auth]	The secret that clients must send to the local A2A server.
env in the authentication of a remote agent profile	The secret for a remote A2A agent.
env values of an MCP server in mcp.toml	The host variables that are passed on to the server. The map goes from the name the server sees to the host name.

Variables set by herdr

herdr sets these when it starts Loom as a plugin. You do not set them. The loomcoding-herdr plugin reads them.

Variable	What it holds
HERDR_ENV	1 when Loom runs inside herdr.
HERDR_PLUGIN_CONTEXT_JSON	The context of the workspace, as JSON.
HERDR_PANE_ID	The identifier of the pane.
HERDR_PLUGIN_ID	The identifier of the plugin.
HERDR_BIN_PATH	The path of the herdr program. Default: herdr.

Variables seen by commands that Loom runs

The bash tool does not pass your whole environment to the commands it runs. It passes a fixed list of system variables, among them PATH, SYSTEMROOT, TEMP, HOME, USERPROFILE, LANG, CARGO_HOME and RUSTUP_HOME. It also passes the variables of the project .env file. Other variables of your shell are not passed.

Next steps

• Configuration (loomcoding.toml)
• Profile folders
• Commands