Zench is a lightweight benchmarking library for Rust, built for seamless workflow integration, speed, and productivity. Run benchmarks anywhere in your codebase and integrate performance checks directly into your cargo test pipeline.

• Benchmark everywhere - in src/, tests/, examples/, benches/, including private functions
• Data manipulation - filter, inspect, and act on benchmark results in code
• Performance Assertions - warn or panic when performance expectations are not met
• Cargo-native - runs with cargo test and cargo bench
• Zero dependencies - pure Rust standard library
• Stable Rust - no nightly required

cargo add zench

or

[dependencies]
zench = "0.2.1"

use zench::bench;
use zench::bx;

// the function to be benchmarked
fn fibonacci(n: u64) -> u64 {
    match n {
        0 => 1,
        1 => 1,
        n => fibonacci(n - 1) + fibonacci(n - 2),
    }
}

#[test]
fn bench_fib() {
    bench!(
        "fib 10" => fibonacci(bx(10))       
    );
}

Run the benchmark test

cargo test bench --release

You'll get a detailed report directly in your terminal:

───────┬───────────┬───────┬────────────┬──────────┬──────────────
 name  │  median   │  cv   │  std.dev   │ outliers │ samples/iters
───────┼───────────┼───────┼────────────┼──────────┼──────────────
fib 10 │ 106.416ns │ 0.22% │  ± 0.233ns │    2.78% │  36 / 524,288
───────┴───────────┴───────┴────────────┴──────────┴──────────────
total time: 2.239029501 sec
rust: 1.94.1 (release) | zench: 0.2.x

You can also test many cases at once

#[test]
fn bench_fibs() {
    bench!(
        "fib 10" => fibonacci(bx(10)),
        "fib 20" => fibonacci(bx(20)),
        "fib 30" => fibonacci(bx(30)),
    );
}

// Alternative: using a loop

#[test]
fn bench_fibs() {
    let mut b = bench!();

    for case in [10, 20, 30] {
        b.bench(case, || {
            fibonacci(bx(case));
        });
    }
}

Result

───────┬───────────┬───────┬─────────────┬──────────┬──────────────
 name  │  median   │  cv   │   std.dev   │ outliers │ samples/iters
───────┼───────────┼───────┼─────────────┼──────────┼──────────────
fib 10 │ 106.512ns │ 0.39% │   ± 0.415ns │    0.00% │  36 / 524,288
fib 20 │  13.398µs │ 0.35% │   ± 0.047µs │    0.00% │   10 / 16,384
fib 30 │   1.651ms │ 0.41% │   ± 0.007ms │    0.00% │      10 / 128
───────┴───────────┴───────┴─────────────┴──────────┴──────────────
total time: 7.41873511 sec
rust: 1.94.1 (release) | zench: 0.2.x

Zench provides access to all benchmark metrics through the report API, allowing you to manipulate them in code.

1. bench! measures and prints the default report with benchmark data
2. Report (optional) lets you manipulate benchmark data and report output

Focus on the data that matters by sorting or limiting results.

This example sorts benchmark results, keeps only the two fastest entries, and adds a title to identify the group.

#[test]
fn bench_fibs() {
    bench!(
        "fib 10" => fibonacci(bx(10)),
        "fib 5"  => fibonacci(bx(5)),
        "fib 12" => fibonacci(bx(12)),
        "fib 8"  => fibonacci(bx(8)),
    )
    .report(|r| {
        let (mut faster_group, mut slower_group) = r
            .sort_by_median() // Sort benchmarks by median time
            .filter_n(2)      // Keep the first two results
            .split();         // split at current state

        faster_group
            .title("Top 2")   // Define a group title
            .print();         // Print the results

        slower_group
            .title("Rest")    // Define a group title
            .print();         // Print the results
    });
}

The output will look like this:

Top 2 > Sort Median > Filter N(2)
──────┬──────────┬───────┬────────────┬──────────┬──────────────
name  │  median  │  cv   │  std.dev   │ outliers │ samples/iters
──────┼──────────┼───────┼────────────┼──────────┼──────────────
fib 5 │  9.299ns │ 0.58% │  ± 0.054ns │    4.00% │ 100 / 524,288
fib 8 │ 40.298ns │ 0.39% │  ± 0.157ns │    4.21% │  95 / 524,288
──────┴──────────┴───────┴────────────┴──────────┴──────────────

Rest
───────┬───────────┬───────┬────────────┬──────────┬──────────────
 name  │  median   │  cv   │  std.dev   │ outliers │ samples/iters
───────┼───────────┼───────┼────────────┼──────────┼──────────────
fib 10 │ 106.412ns │ 0.39% │  ± 0.416ns │   13.89% │  36 / 524,288
fib 12 │ 279.791ns │ 0.66% │  ± 1.852ns │    0.00% │  14 / 524,288
───────┴───────────┴───────┴────────────┴──────────┴──────────────
total time: 7.075344703 sec
rust: 1.94.1 (release) | zench: 0.2.x

issue! is a Zench macro that emits a warn diagnostic message by default. It is used as a replacement for print!, debug!, or panic! because its behavior can change depending on configuration.

issue! can be configured to panic if the ZENCH environment variable is set to panic:

ZENCH=panic

Currently, Zench focuses on relative comparisons and regression detection within the same run.

In many cases, you already know the expected baseline or acceptable range for a function, and you can assert that directly in the benchmark.

For example, if a function normally takes around 1 ms, you can simply fail the test if it exceeds 15% regression.

#[test]
fn bench_simple_regression_example() {
    bench!(
        "my func" => sleep(Duration::from_millis(1)),
    )
    .report(|r| {
        r.print();

        // Expected baseline time
        let baseline = Duration::from_millis(1).as_nanos() as f64;
        let tolerance = 0.15; // 15%

        // get the first benchmark time (median)
        let median = r
            .first()
            .unwrap()
            .median();

        let upper = baseline * (1.0 + tolerance);
        let lower = baseline * (1.0 - tolerance);

        if median > upper {
            issue!("relative regression (>15%)");
        }

        if median < lower {
            issue!("performance improvement (>15%)");
        }

        // Note: Ensure the system is in a stable state
        // during benchmarking, as background activity
        // can influence the results.

        // Note: Fixed baseline values may vary across
        // different hardware. Adjust the baseline
        // accordingly for your system.
    });
}

See zench_examples/ for a variety of examples.

Zench integrates with cargo test and cargo bench

With cargo test

# Run only tests with names starting with "bench_"
cargo test bench --release

# or
cargo test bench --release -- --no-capture

With cargo bench

cargo bench

# Also add the traditional benchmark configuration to Cargo.toml
# [[bench]]
# name = ""
# harness = false

Run benchmarks directly from your editor by clicking ▶ Run Test. See the pre-configured setups.

• Function naming: It is recommended that Benchmark test functions start with bench_ to enable filtering via Cargo. Zench follows Cargo's test filtering conventions to distinguish between regular tests and benchmark tests.

// cargo test bench --release
#[test]
fn bench_fib() {
    // benchmark code
}

• Requires release profile - To ensure accurate results. Debug profile includes overhead and lack the optimizations necessary for realistic performance measurements.

• Compiler Optimization (Dead Code Elimination) - To prevent the compiler from optimizing away your benchmark code, you must wrap inputs and outputs with bx(). This is a thin wrapper around std::hint::black_box, which you can also use directly.

• Platform Support – Currently developed and tested primarily on Linux (Fedora). Feedback from Windows and macOS users is highly appreciated.

• Shared environments – Benchmarking on heavily loaded systems, shared CI runners, or virtual machines may produce unstable or "noisy" measurements.

• Not a profiler – Zench measures execution time and stability; it does not provide CPU flame graphs or memory allocation analysis.

Zench is the "alarm" that tells you performance changed. A profiler is the diagnostic tool that helps you find the cause.

• Documentation - Still in progress as the API stabilizes.

Zench is in early development. APIs and behavior may change between releases while the project stabilizes.

• Rust stable 1.87.0 or newer (MSRV)

Dual-licensed under MIT and Apache 2.0

Copyright (c) 2026-present Envidera