# Package indexes

By default, uv uses the [Python Package Index (PyPI)](https://pypi.org) for dependency resolution
and package installation. However, uv can be configured to use other package indexes, including
private indexes, via the `[[tool.uv.index]]` configuration option (and `--index`, the analogous
command-line option).

## Defining an index

To include an additional index when resolving dependencies, add a `[[tool.uv.index]]` entry to your
`pyproject.toml`:

```toml
[[tool.uv.index]]
# Optional name for the index.
name = "pytorch"
# Required URL for the index.
url = "https://download.pytorch.org/whl/cpu"
```

Indexes are prioritized in the order in which they’re defined, such that the first index listed in
the configuration file is the first index consulted when resolving dependencies, with indexes
provided via the command line taking precedence over those in the configuration file.

By default, uv includes the Python Package Index (PyPI) as the "default" index, i.e., the index used
when a package is not found on any other index. To exclude PyPI from the list of indexes, set
`default = true` on another index entry (or use the `--default-index` command-line option):

```toml
[[tool.uv.index]]
name = "pytorch"
url = "https://download.pytorch.org/whl/cpu"
default = true
```

The default index is always treated as lowest priority, regardless of its position in the list of
indexes.

Index names may only contain alphanumeric characters, dashes, underscores, and periods, and must be
valid ASCII.

When providing an index on the command line (with `--index` or `--default-index`) or through an
environment variable (`UV_INDEX` or `UV_DEFAULT_INDEX`), names are optional but can be included
using the `<name>=<url>` syntax, as in:

```shell
# On the command line.
$ uv lock --index pytorch=https://download.pytorch.org/whl/cpu
# Via an environment variable.
$ UV_INDEX=pytorch=https://download.pytorch.org/whl/cpu uv lock
```

## Pinning a package to an index

A package can be pinned to a specific index by specifying the index in its `tool.uv.sources` entry.
For example, to ensure that `torch` is _always_ installed from the `pytorch` index, add the
following to your `pyproject.toml`:

```toml
[tool.uv.sources]
torch = { index = "pytorch" }

[[tool.uv.index]]
name = "pytorch"
url = "https://download.pytorch.org/whl/cpu"
```

Similarly, to pull from a different index based on the platform, you can provide a list of sources
disambiguated by environment markers:

```toml title="pyproject.toml"
[project]
dependencies = ["torch"]

[tool.uv.sources]
torch = [
  { index = "pytorch-cu118", marker = "sys_platform == 'darwin'"},
  { index = "pytorch-cu124", marker = "sys_platform != 'darwin'"},
]

[[tool.uv.index]]
name = "pytorch-cu118"
url = "https://download.pytorch.org/whl/cu118"

[[tool.uv.index]]
name = "pytorch-cu124"
url = "https://download.pytorch.org/whl/cu124"
```

An index can be marked as `explicit = true` to prevent packages from being installed from that index
unless explicitly pinned to it. For example, to ensure that `torch` is installed from the `pytorch`
index, but all other packages are installed from PyPI, add the following to your `pyproject.toml`:

```toml
[tool.uv.sources]
torch = { index = "pytorch" }

[[tool.uv.index]]
name = "pytorch"
url = "https://download.pytorch.org/whl/cpu"
explicit = true
```

Named indexes referenced via `tool.uv.sources` must be defined within the project's `pyproject.toml`
file; indexes provided via the command-line, environment variables, or user-level configuration will
not be recognized.

If an index is marked as both `default = true` and `explicit = true`, it will be treated as an
explicit index (i.e., only usable via `tool.uv.sources`) while also removing PyPI as the default
index.

## Searching across multiple indexes

By default, uv will stop at the first index on which a given package is available, and limit
resolutions to those present on that first index (`first-index`).

For example, if an internal index is specified via `[[tool.uv.index]]`, uv's behavior is such that
if a package exists on that internal index, it will _always_ be installed from that internal index,
and never from PyPI. The intent is to prevent "dependency confusion" attacks, in which an attacker
publishes a malicious package on PyPI with the same name as an internal package, thus causing the
malicious package to be installed instead of the internal package. See, for example,
[the `torchtriton` attack](https://pytorch.org/blog/compromised-nightly-dependency/) from
December 2022.

Users can opt in to alternate index behaviors via the`--index-strategy` command-line option, or the
`UV_INDEX_STRATEGY` environment variable, which supports the following values:

- `first-index` (default): Search for each package across all indexes, limiting the candidate
  versions to those present in the first index that contains the package.
- `unsafe-first-match`: Search for each package across all indexes, but prefer the first index with
  a compatible version, even if newer versions are available on other indexes.
- `unsafe-best-match`: Search for each package across all indexes, and select the best version from
  the combined set of candidate versions.

While `unsafe-best-match` is the closest to pip's behavior, it exposes users to the risk of
"dependency confusion" attacks.

## Authentication

Most private package indexes require authentication to access packages, typically via a username and
password (or access token).

!!! tip

    See the [alternative index guide](../guides/integration/alternative-indexes.md) for details on
    authenticating with specific private index providers, e.g., from AWS, Azure, or GCP.

### Providing credentials directly

Credentials can be provided directly via environment variables or by embedding them in the URL.

For example, given an index named `internal-proxy` that requires a username (`public`) and password
(`koala`), define the index (without credentials) in your `pyproject.toml`:

```toml
[[tool.uv.index]]
name = "internal-proxy"
url = "https://example.com/simple"
```

From there, you can set the `UV_INDEX_INTERNAL_PROXY_USERNAME` and
`UV_INDEX_INTERNAL_PROXY_PASSWORD` environment variables, where `INTERNAL_PROXY` is the uppercase
version of the index name, with non-alphanumeric characters replaced by underscores:

```sh
export UV_INDEX_INTERNAL_PROXY_USERNAME=public
export UV_INDEX_INTERNAL_PROXY_PASSWORD=koala
```

By providing credentials via environment variables, you can avoid storing sensitive information in
the plaintext `pyproject.toml` file.

Alternatively, credentials can be embedded directly in the index definition:

```toml
[[tool.uv.index]]
name = "internal"
url = "https://public:koala@pypi-proxy.corp.dev/simple"
```

For security purposes, credentials are _never_ stored in the `uv.lock` file; as such, uv _must_ have
access to the authenticated URL at installation time.

### Using credential providers

In addition to providing credentials directly, uv supports discovery of credentials from netrc and
keyring. See the [HTTP authentication](./authentication.md#http-authentication) documentation for
details on setting up specific credential providers.

By default, uv will attempt an unauthenticated request before querying providers. If the request
fails, uv will search for credentials. If credentials are found, an authenticated request will be
attempted.

!!! note

    If a username is set, uv will search for credentials before making an unauthenticated request.

Some indexes (e.g., GitLab) will forward unauthenticated requests to a public index, like PyPI —
which means that uv will not search for credentials. This behavior can be changed per-index, using
the `authenticate` setting. For example, to always search for credentials:

```toml hl_lines="4"
[[tool.uv.index]]
name = "example"
url = "https://example.com/simple"
authenticate = "always"
```

When `authenticate` is set to `always`, uv will eagerly search for credentials and error if
credentials cannot be found.

### Disabling authentication

To prevent leaking credentials, authentication can be disabled for an index:

```toml hl_lines="4"
[[tool.uv.index]]
name = "example"
url = "https://example.com/simple"
authenticate = "never"
```

When `authenticate` is set to `never`, uv will never search for credentials for the given index and
will error if credentials are provided directly.

## "Flat" indexes

By default, `[[tool.uv.index]]` entries are assumed to be PyPI-style registries that implement the
[PEP 503](https://peps.python.org/pep-0503/) Simple Repository API. However, uv also supports "flat"
indexes, which are local directories or HTML pages that contain flat lists of wheels and source
distributions. In pip, such indexes are specified using the `--find-links` option.

To define a flat index in your `pyproject.toml`, use the `kind = "flat"` option:

```toml
[[tool.uv.index]]
name = "example"
url = "/path/to/directory"
kind = "flat"
```

Flat indexes support the same feature set as Simple Repository API indexes (e.g.,
`explicit = true`); you can also pin a package to a flat index using `tool.uv.sources`.

## `--index-url` and `--extra-index-url`

In addition to the `[[tool.uv.index]]` configuration option, uv supports pip-style `--index-url` and
`--extra-index-url` command-line options for compatibility, where `--index-url` defines the default
index and `--extra-index-url` defines additional indexes.

These options can be used in conjunction with the `[[tool.uv.index]]` configuration option, and
follow the same prioritization rules:

- The default index is always treated as lowest priority, whether defined via the legacy
  `--index-url` argument, the recommended `--default-index` argument, or a `[[tool.uv.index]]` entry
  with `default = true`.
- Indexes are consulted in the order in which they’re defined, either via the legacy
  `--extra-index-url` argument, the recommended `--index` argument, or `[[tool.uv.index]]` entries.

In effect, `--index-url` and `--extra-index-url` can be thought of as unnamed `[[tool.uv.index]]`
entries, with `default = true` enabled for the former. In that context, `--index-url` maps to
`--default-index`, and `--extra-index-url` maps to `--index`.
