uv/docs/configuration/environment.md

Environment variables

uv accepts the following command-line arguments as environment variables:

• UV_INDEX_URL: Equivalent to the --index-url command-line argument. If set, uv will use this URL as the base index for searching for packages.
• UV_EXTRA_INDEX_URL: Equivalent to the --extra-index-url command-line argument. If set, uv will use this space-separated list of URLs as additional indexes when searching for packages.
• UV_CACHE_DIR: Equivalent to the --cache-dir command-line argument. If set, uv will use this directory for caching instead of the default cache directory.
• UV_NO_CACHE: Equivalent to the --no-cache command-line argument. If set, uv will not use the cache for any operations.
• UV_RESOLUTION: Equivalent to the --resolution command-line argument. For example, if set to lowest-direct, uv will install the lowest compatible versions of all direct dependencies.
• UV_PRERELEASE: Equivalent to the --prerelease command-line argument. For example, if set to allow, uv will allow pre-release versions for all dependencies.
• UV_SYSTEM_PYTHON: Equivalent to the --system command-line argument. If set to true, uv will use the first Python interpreter found in the system PATH. WARNING: UV_SYSTEM_PYTHON=true is intended for use in continuous integration (CI) or containerized environments and should be used with caution, as modifying the system Python can lead to unexpected behavior.
• UV_PYTHON: Equivalent to the --python command-line argument. If set to a path, uv will use this Python interpreter for all operations.
• UV_BREAK_SYSTEM_PACKAGES: Equivalent to the --break-system-packages command-line argument. If set to true, uv will allow the installation of packages that conflict with system-installed packages. WARNING: UV_BREAK_SYSTEM_PACKAGES=true is intended for use in continuous integration (CI) or containerized environments and should be used with caution, as modifying the system Python can lead to unexpected behavior.
• UV_NATIVE_TLS: Equivalent to the --native-tls command-line argument. If set to true, uv will use the system's trust store instead of the bundled webpki-roots crate.
• UV_INDEX_STRATEGY: Equivalent to the --index-strategy command-line argument. For example, if set to unsafe-any-match, uv will consider versions of a given package available across all index URLs, rather than limiting its search to the first index URL that contains the package.
• UV_REQUIRE_HASHES: Equivalent to the --require-hashes command-line argument. If set to true, uv will require that all dependencies have a hash specified in the requirements file.
• UV_CONSTRAINT: Equivalent to the --constraint command-line argument. If set, uv will use this file as the constraints file. Uses space-separated list of files.
• UV_BUILD_CONSTRAINT: Equivalent to the --build-constraint command-line argument. If set, uv will use this file as constraints for any source distribution builds. Uses space-separated list of files.
• UV_OVERRIDE: Equivalent to the --override command-line argument. If set, uv will use this file as the overrides file. Uses space-separated list of files.
• UV_LINK_MODE: Equivalent to the --link-mode command-line argument. If set, uv will use this as a link mode.
• UV_NO_BUILD_ISOLATION: Equivalent to the --no-build-isolation command-line argument. If set, uv will skip isolation when building source distributions.
• UV_CUSTOM_COMPILE_COMMAND: Equivalent to the --custom-compile-command command-line argument. Used to override uv in the output header of the requirements.txt files generated by uv pip compile. Intended for use-cases in which uv pip compile is called from within a wrapper script, to include the name of the wrapper script in the output file.
• UV_KEYRING_PROVIDER: Equivalent to the --keyring-provider command-line argument. If set, uv will use this value as the keyring provider.
• UV_CONFIG_FILE: Equivalent to the --config-file command-line argument. Expects a path to a local uv.toml file to use as the configuration file.
• UV_NO_CONFIG: Equivalent to the --no-config command-line argument. If set, uv will not read any configuration files from the current directory, parent directories, or user configuration directories.
• UV_EXCLUDE_NEWER: Equivalent to the --exclude-newer command-line argument. If set, uv will exclude distributions published after the specified date.
• UV_PYTHON_PREFERENCE: Equivalent to the --python-preference command-line argument. Whether uv should prefer system or managed Python versions.
• UV_PYTHON_DOWNLOADS: Equivalent to the python-downloads setting and, when disabled, the --no-python-downloads option. Whether uv should allow Python downloads.
• UV_COMPILE_BYTECODE: Equivalent to the --compile-bytecode command-line argument. If set, uv will compile Python source files to bytecode after installation.

In each case, the corresponding command-line argument takes precedence over an environment variable.

In addition, uv respects the following environment variables:

• UV_CONCURRENT_DOWNLOADS: Sets the maximum number of in-flight concurrent downloads that uv will perform at any given time.
• UV_CONCURRENT_BUILDS: Sets the maximum number of source distributions that uv will build concurrently at any given time.
• UV_CONCURRENT_INSTALLS: Used to control the number of threads used when installing and unzipping packages.
• UV_TOOL_DIR: Used to specify the directory where uv will store managed tools.
• UV_TOOL_BIN_DIR: Used to specify the "bin" directory where uv will install tool executables.
• UV_PYTHON_INSTALL_DIR: Used to specify the directory where uv will store managed Python installations.
• UV_PYTHON_INSTALL_MIRROR: Managed Python installations are downloaded from python-build-standalone. This variable can be set to a mirror URL to use a different source for Python installations. The provided URL will replace https://github.com/indygreg/python-build-standalone/releases/download in, e.g., https://github.com/indygreg/python-build-standalone/releases/download/20240713/cpython-3.12.4%2B20240713-aarch64-apple-darwin-install_only.tar.gz.
• UV_PYPY_INSTALL_MIRROR: Managed PyPy installations are downloaded from python.org. This variable can be set to a mirror URL to use a different source for PyPy installations. The provided URL will replace https://downloads.python.org/pypy in, e.g., https://downloads.python.org/pypy/pypy3.8-v7.3.7-osx64.tar.bz2.
• XDG_CONFIG_HOME: Used to specify the path to uv user-level configuration directory on Unix systems.
• XDG_CACHE_HOME: Used to specify the directory where uv stores cache files on Unix systems.
• XDG_DATA_HOME: Used to specify the directory where uv stores managed Python installations and managed tools on Unix systems.
• XDG_BIN_HOME: Used to specify the directory where executables are installed into.
• SSL_CERT_FILE: If set, uv will use this file as the certificate bundle instead of the system's trust store.
• SSL_CLIENT_CERT: If set, uv will use this file for mTLS authentication. This should be a single file containing both the certificate and the private key in PEM format.
• RUST_LOG: If set, uv will use this value as the log level for its --verbose output. Accepts any filter compatible with the tracing_subscriber crate. For example, RUST_LOG=trace will enable trace-level logging. See the tracing documentation for more.
• HTTP_PROXY, HTTPS_PROXY, ALL_PROXY: The proxy to use for all HTTP/HTTPS requests.
• HTTP_TIMEOUT (or UV_HTTP_TIMEOUT): If set, uv will use this value (in seconds) as the timeout for HTTP reads (default: 30 s).
• PYC_INVALIDATION_MODE: The validation modes to use when run with --compile. See: PycInvalidationMode.
• VIRTUAL_ENV: Used to detect an activated virtual environment.
• CONDA_PREFIX: Used to detect an activated Conda environment.
• PROMPT: Used to detect the use of the Windows Command Prompt (as opposed to PowerShell).
• NU_VERSION: Used to detect the use of NuShell.
• FISH_VERSION: Used to detect the use of the Fish shell.
• BASH_VERSION: Used to detect the use of the Bash shell.
• ZSH_VERSION: Used to detect the use of the Zsh shell.
• MACOSX_DEPLOYMENT_TARGET: Used with --python-platform macos and related variants to set the deployment target (i.e., the minimum supported macOS version). Defaults to 12.0, the least-recent non-EOL macOS version at time of writing.
• NO_COLOR: Disable colors. Takes precedence over FORCE_COLOR. See no-color.org.
• FORCE_COLOR: Enforce colors regardless of TTY support. See force-color.org.