How to Prepare Your Rust Crate for the New docs.rs Default Build Target Policy

Introduction

Starting May 1, 2026, docs.rs will change its default build behavior: instead of building documentation for five targets, it will build for only the default target (x86_64-unknown-linux-gnu) unless you explicitly request additional targets. This change affects new releases and rebuilds of old releases. It reduces build times and saves resources—most crates don’t compile different code per target anyway. This guide walks you through the steps to ensure your crate’s documentation is built for the right targets after the change.

What You Need

• A Cargo.toml file for your Rust crate.
• A basic understanding of target triples (e.g., x86_64-unknown-linux-gnu).
• Knowledge of whether your crate uses platform-specific code (e.g., cfg(target_os)).
• Access to the docs.rs platform (or its build commands for testing).

Step-by-Step Guide

Step 1: Understand the New Default Behavior

Before May 1, 2026, if your Cargo.toml doesn’t specify a targets list under [package.metadata.docs.rs], docs.rs builds for five hardcoded targets: x86_64-unknown-linux-gnu, x86_64-apple-darwin, x86_64-pc-windows-msvc, i686-unknown-linux-gnu, and i686-pc-windows-msvc. After the change, it will build only the default target (x86_64-unknown-linux-gnu) unless you override it or request more. This change only affects new releases and rebuilds after that date.

Step 2: Determine If Your Crate Needs Multiple Targets

Ask yourself: Does your crate compile different code or use different dependencies depending on the target platform? If it uses cfg(target_os), cfg(target_arch), or platform-specific conditional compilation, you likely need documentation built for multiple targets. If not—most crates are cross-platform without conditional logic—you’re fine with just the default. For example, a library that works on Linux, macOS, and Windows without any cfg checks doesn’t need multiple builds. The docs will appear identical anyway.

Step 3: Override the Default Target (Optional)

If you want a different default target than the Linux x86_64, you can set default-target in your [package.metadata.docs.rs] section. This is useful if your crate is primarily developed for macOS or Windows. Add the following to your Cargo.toml:

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

This tells docs.rs to build documentation for x86_64-apple-darwin by default. If you also want other targets, you must still list them explicitly in the targets array (see Step 4).

Step 4: Explicitly List All Required Targets

If your crate absolutely needs documentation built for more than one target (e.g., because it uses conditional compilation that changes the documentation), you must define the full list using the targets key. This overrides any defaults. Example:

[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 available in the Rust toolchain. If you want to keep the exact same behavior as before the change, copy the five targets from the original list above.

Step 5: Apply Changes to Existing Releases

The change affects only new releases and rebuilds of old releases. If you have an existing release that was built before May 1, 2026, its documentation will remain unchanged. To trigger a rebuild with the new target behavior, you must explicitly request a rebuild on docs.rs (usually by pushing a new version or using the rebuild interface). After rebuilding, the documentation will use the new target logic based on what you set in your Cargo.toml.

Tips for a Smooth Transition

• Check your existing metadata: If you already have a targets list in [package.metadata.docs.rs], the change will not affect you—your list will continue to be used. If you don’t, you’ll need to decide whether to add one or accept the simplified default.
• Use conditional compilation wisely: If your crate uses cfg to include platform-specific code, ensure that the documentation generated for the default target still represents the full API. For features exclusive to another platform, consider documenting them with a note that they require that target.
• Test locally with docs.rs build commands: You can simulate what docs.rs will do by running cargo doc --target x86_64-unknown-linux-gnu (or your chosen default). Use cargo doc --target ALL on nightly to see all targets, but note that docs.rs only uses the targets you specify.
• Consider resource savings: Building fewer targets reduces build time and docs.rs resource consumption. If you don’t need multiple targets, leaving it at the default helps the platform and your users.
• Keep documentation clear: If you drop a target, users of that platform may still see documentation that compiles fine—they just won’t have a separate build. Most documentation is platform-agnostic, so this is rarely an issue.

By following these steps, you’ll ensure your crate’s documentation continues to be built correctly and efficiently after May 1, 2026. Remember: the change is only in the default behavior; you retain full control over which targets are built.