Environment variables

BIOME_LOG_PREFIX_NAME

A prefix that’s added to the name of the log. Default: server.log.

BIOME_LOG_PATH

The directory where the Daemon logs will be saved.

BIOME_CONFIG_PATH

A path to the configuration file

BIOME_BINARY

Overrides the Biome binary being used. This allows you, for example, to use a system-wide Biome binary.

If you don’t define this variable, Biome will automatically detect the correct binary for your platform.

# Nix derivation example; the binary path comes from "${pkgs.biome}/bin/biome"
BIOME_BINARY=/nix/store/68fyfw1hidsqkal1839whi3nzgvqv4pa-biome-1.0.0/bin/biome npx @biomejs/biome format .

RAYON_NUM_THREADS

Controls the number of threads used by Biome’s internal thread pool (via the Rayon library). This environment variable applies to all Biome commands, not just the ci command.

Useful for:

• Limiting CPU usage in resource-constrained environments
• Running multiple Biome processes in parallel (e.g., in monorepos or agentic workflows)
• Preventing resource contention when multiple agents/processes run Biome simultaneously

# Limit Biome to use only 1 thread
RAYON_NUM_THREADS=1 biome lint .

# Set globally for all Biome commands
export RAYON_NUM_THREADS=2