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cargo-llvm-cov

cargo-llvm-cov is a cargo subcommand (Apache-2.0 or MIT) for LLVM source-based code coverage in Rust, supporting cargo test, cargo run and cargo nextest with precise line and region coverage.

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Introduction

cargo-llvm-cov is a cargo subcommand that makes it easy to use LLVM source-based code coverage, a wrapper around rustc’s -C instrument-coverage. Its README lists the benefits: very precise coverage data (line, region and branch, with branch coverage currently optional and requiring nightly), support for cargo test, cargo run and cargo nextest with a cargo-compatible CLI, support for proc macros including UI tests, optional doc test coverage on nightly, and speed, because it only instruments necessary crates.

Reports can be printed as a summary, opened as HTML (--open), or exported in LCOV, JSON, Cobertura and Codecov formats for CI services. It can merge coverage from different test conditions, measure coverage of C/C++ code linked into Rust, cover external tests and AFL fuzzers, and exclude files. It is maintained by taiki-e, and version 0.9.1 was released on 6 September 2026.

The source code is at taiki-e/cargo-llvm-cov on GitHub under the Apache-2.0 or MIT licence, with about 1,500 stars; the most recent commit was on 1 November 2026.

Features

  1. Precise coverage: LLVM line and region coverage.
  2. nextest support: cargo llvm-cov nextest.
  3. Many formats: HTML, LCOV, JSON, Cobertura and Codecov.
  4. Advanced scenarios: Merge runs, C/C++ code, external tests and fuzzers.

Pros

  1. Free to use: Open source under the Apache-2.0 or MIT licence, so the core tool costs nothing to use.
  2. Actively maintained: The repository had commits as recent as 1 November 2026.

Cons

  1. Nightly for some features: Branch and doc test coverage need nightly Rust.
  2. Requires llvm-tools: Install the llvm-tools-preview component.
cargo install cargo-llvm-cov --locked
rustup component add llvm-tools-preview
cargo llvm-cov --open
cargo llvm-cov nextest --lcov --output-path lcov.info

Resources:

Pricing

cargo-llvm-cov is free and open source under the Apache-2.0 or MIT licence.

  1. Rust teams needing accurate coverage, especially with nextest.
  2. Projects uploading to Codecov or similar services.

Conclusion

cargo-llvm-cov is the most precise and flexible way to measure Rust coverage, integrating cleanly with cargo and nextest.

Alternatives

Other tools on CheckOps that cover similar ground. Open a page, or compare one with cargo-llvm-cov side by side.