Preparing Your Rust Crate for docs.rs's Default Target Change

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Introduction

If you maintain a Rust crate and rely on docs.rs for automatic documentation hosting, you'll want to pay attention to an important update coming on 2026-05-01. Currently, when you don't specify a list of build targets, docs.rs builds documentation for five default targets. After that date, it will build only for the default target (usually x86_64-unknown-linux-gnu) unless you explicitly ask for more. This change reduces build times, saves server resources, and better matches the needs of most crates that don't compile platform-specific code.

Preparing Your Rust Crate for docs.rs's Default Target Change — Source: blog.rust-lang.org

This guide walks you through what the change means, how to check if your crate is affected, and the exact steps you need to take to update your Cargo.toml metadata so your documentation continues to build as expected.

What You Need

Your Rust crate’s source code – specifically its Cargo.toml file.
Basic familiarity with TOML syntax – you'll be adding or modifying a [package.metadata.docs.rs] section.
Knowledge of your crate’s target requirements – does it use conditional compilation that differs by platform? Are there features that only work on certain OSes?
A way to test documentation builds locally (optional but recommended) – for instance via cargo doc with the same target.

Step-by-Step Guide

Step 1: Understand the Upcoming Change

Before you change anything, make sure you grasp the scope. The new behavior applies only to:

New releases – crates you publish after 2026-05-01.
Rebuilds – if you request a rebuild of an older release, it will also follow the new default.

If your crate currently relies on any of the five default targets (which include x86_64-unknown-linux-gnu, x86_64-apple-darwin, x86_64-pc-windows-msvc, i686-unknown-linux-gnu, and i686-pc-windows-msvc), you may need to act. Most crates don't compile platform-specific code, so for them only the default target matters. If that's your case, you may not need to do anything – but it's wise to confirm.

Step 2: Determine Your Crate's Target Requirements

Look at your crate’s code and dependencies. Ask yourself:

Do I use #[cfg(target_os = "...")] or similar conditional compilation?
Do I depend on platform-specific libraries (e.g., winapi on Windows)?
Do I need to show documentation for different targets in the docs? (For example, some API may only be available on certain platforms.)

If the answer to all is no, you can likely keep the default and ignore the rest of this guide. However, if your crate does vary per target, proceed to the next step.

Step 3: Override the Default Target (Optional)

By default, docs.rs uses x86_64-unknown-linux-gnu as the sole target. If you want a different single target to be the new default, you can set default-target in your package.metadata.docs.rs section:

[package.metadata.docs.rs]
default-target = "x86_64-apple-darwin"

This tells docs.rs: “Build only for this one target unless I add more.” This is useful if your crate is primarily used on macOS, for example.

Step 4: Specify an Explicit Target List (If Needed)

If you need documentation for multiple targets (the old five, or a custom set), you must list them explicitly under the targets key:

[package.metadata.docs.rs]
targets = [
    "x86_64-unknown-linux-gnu",
    "x86_64-apple-darwin",
    "x86_64-pc-windows-msvc",
    "i686-unknown-linux-gnu",
    "i686-pc-windows-msvc"
]

When targets is set, docs.rs builds documentation exactly for those targets – no more, no less. You can include any target supported by the Rust toolchain. For example, if your crate only works on ARM Linux, you could list "aarch64-unknown-linux-gnu".

Note: If you set targets, the default-target field is ignored. The two are mutually exclusive – pick one approach.

Step 5: Test and Rebuild Your Documentation

After updating your Cargo.toml, it's a good idea to verify that the configuration works. You can test locally with:

cargo doc --target x86_64-unknown-linux-gnu
cargo doc --target x86_64-apple-darwin  # etc.

This simulates what docs.rs will do. If you've set an explicit target list, you may want to check that each target produces the expected documentation.

Once satisfied, commit and push your changes. When you publish a new release after 2026-05-01, docs.rs will apply your new settings. If you need to rebuild older releases with the new behavior, you can use the “rebuild” option on the docs.rs page.

Tips

Don’t over-specify targets – Adding many targets increases build time and resource usage. Only include the ones that are genuinely relevant to your crate’s audience.
Leverage the default-target shortcut – If you only need one platform besides Linux, just set default-target and you're done.
Check the docs.rs build logs – After a rebuild, review the log to confirm your targets are being built.
Communicate with downstream users – If your crate provides platform-specific documentation, let users know which targets you support.
Keep your metadata consistent – If you have a workspace with multiple crates, ensure each one has the appropriate docs.rs configuration.

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