Adapting to docs.rs Default Target Changes: A Step-by-Step Guide

Introduction

Starting May 1, 2026, docs.rs will shift its default build behavior—instead of building documentation for five targets, it will only compile for the default target unless you explicitly request more. This change, which builds on a 2020 opt-in feature, aims to reduce build times and conserve resources since most crates don’t vary code across platforms. If you maintain a Rust crate, this guide walks you through understanding the update, checking your setup, and configuring multiple targets when needed.

Adapting to docs.rs Default Target Changes: A Step-by-Step Guide — Source: blog.rust-lang.org

What You Need

A Rust crate with a Cargo.toml file
Access to the crate’s repository where you can edit its Cargo.toml
Basic familiarity with [package.metadata.docs.rs] settings (optional but helpful)

Step 1: Understand the Default Target Selection

docs.rs automatically picks a default target when none is specified. As of the change, if you don’t set default-target in your [package.metadata.docs.rs], the system uses x86_64-unknown-linux-gnu—the architecture of its build servers. To see which target will be used for your crate, simply note that unless you override it, your documentation will be built for Linux x86_64.

Step 2: Decide If Your Crate Needs Multiple Targets

Ask yourself: Does your crate compile different code depending on the target triple? For instance, if you use #[cfg(target_os = "windows")] or platform-specific dependencies, you may want documentation for each relevant platform. Most crates, however, produce identical docs across targets, so one build is sufficient. If you’re unsure, check your cfg attributes or conditional compilation logic.

Step 3: Check Your Current docs.rs Configuration

Open your Cargo.toml and look for a [package.metadata.docs.rs] section. If it exists, note whether it contains a targets list or a default-target setting. If it doesn’t exist, that’s fine—your crate will fall under the new default behavior (single target).

Step 4: Explicitly Set the Default Target (Optional)

If you want to change the default target (e.g., to macOS for testing), add the following to your Cargo.toml:

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

This tells docs.rs to use that target when no other targets are listed. It only affects the “default” build—not additional targets you might define later.

Step 5: Define Additional Targets (If Needed)

For crates that genuinely require documentation on multiple platforms, specify the full list explicitly using the targets key. For 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 exactly those targets—no more, no less. You can include any target supported by the Rust toolchain; only the default behavior is changing.

Step 6: Test with a New Release or Rebuild

The change affects new releases and rebuilds of old releases. After updating your Cargo.toml, publish a new version of your crate or trigger a rebuild on docs.rs. Verify that the documentation builds for the expected targets by visiting your crate’s page on docs.rs and checking the target selector dropdown.

Step 7: Monitor and Adjust Over Time

If you later add conditional compilation for a new platform, return to this guide and update your targets list accordingly. Keep in mind that docs.rs still supports any Rust target—only the default list shrank from five to one.

Tips

Most crates don’t need multiple targets. Save build time and resources by sticking with the default single target unless your crate uses platform-specific code.
Use default-target sparingly. It’s mainly for cases where you want a different primary platform than the build server’s Linux.
Keep your targets list lean. Only include the platforms your crate actually supports—unnecessary targets waste compute and delay documentation generation.
Test before the deadline. The cutoff is May 1, 2026. Update your configuration now to avoid surprises when publishing new releases after that date.
Review docs.rs documentation. For advanced options like all-features or rustdoc-args, check the official docs.rs metadata docs.

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