How can I download Rust API docs?

Another way to have the Rust docs (and a few others from languages to frameworks to CLI tools) for offline use is to install Zeal for Linux or Dash for OS X and download Rust's documentation from there.

I recommend adding a link to file:///usr/local/share/doc/rust/html/index.html in your browser/desktops bookmarks.

If you're running Arch, install rust-docs and navigate to file:///usr/share/doc/rust/html/index.html.

Rustup

If you use rustup, the recommended way to install and update Rust, then the docs may already be installed; the default installation behavior has changed over time. Try running rustup doc to open them in your browser.

If they aren't already installed, you can download the docs by running rustup component add rust-docs.

By default, rustup doc opens the documentation front page, but you can add --std to jump straight to the standard API docs or --book for The Rust Programming Language. You can also use rustup doc std::iter::Iterator to open the documentation of a specific item.

rustup 1.20 learned the concept of profiles. These allow you to default to having docs installed for a toolchain (via the default profile) or not (via the minimal profile).

Standalone Rust Installer

The Rust installer also installs the documentation for the language and for Cargo. On Linux systems, it can be found at /usr/local/share/doc/{rust,cargo}.