# 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_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`: 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_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_EXCLUDE_NEWER`: Equivalent to the `--exclude-newer` command-line argument. If set, uv will
  exclude distributions published after the specified date.

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

In addition, uv respects the following environment variables:

- `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](https://docs.rs/tracing-subscriber/latest/tracing_subscriber/filter/struct.EnvFilter.html#example-syntax)
  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`](https://docs.python.org/3/library/py_compile.html#py_compile.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](https://no-color.org).
- `FORCE_COLOR`: Enforce colors regardless of TTY support. See [force-color.org](https://force-color.org).