Robust, reliable performance measurement and analysis

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BSD-3-Clause licensed and maintained by Bryan O'Sullivan
This version can be pinned in stack with:criterion-,5323

Criterion: robust, reliable performance measurement

Hackage Build Status

This package provides the Criterion module, a Haskell library for measuring and analysing software performance.

To get started, read the online tutorial, and take a look at the programs in the examples directory.

Building and installing

To build and install criterion, just run

cabal install criterion

Get involved!

Please report bugs via the github issue tracker.

Master github repository:

  • git clone

There’s also a Mercurial mirror:

  • hg clone

(You can create and contribute changes using either Mercurial or git.)


This library is written and maintained by Bryan O’Sullivan, [email protected].


  • criterion was previously reporting the following statistics incorrectly on GHC 8.2 and later:

    • gcStatsBytesAllocated
    • gcStatsBytesCopied
    • gcStatsGcCpuSeconds
    • gcStatsGcWallSeconds

    This has been fixed.

  • The type signature of runBenchmarkable has changed from:

    Benchmarkable -> Int64 -> (a -> a -> a) -> (IO () -> IO a) -> IO a


    Benchmarkable -> Int64 -> (a -> a -> a) -> (Int64 -> IO () -> IO a) -> IO a

    The extra Int64 argument represents how many iterations are being timed.

  • Remove the deprecated getGCStats and applyGCStats functions (which have been replaced by getGCStatistics and applyGCStatistics).

  • Remove the deprecated forceGC field of Config, as well as the corresponding --no-gc command-line option.

  • The header in generated JSON output mistakenly used the string "criterio". This has been corrected to "criterion".

  • Add error bars and zoomable navigation to generated HTML report graphs.

    (Note that there have been reports that this feature can be somewhat unruly when using macOS and Firefox simultaneously. See for more details.)

  • Use a predetermined set of cycling colors for benchmark groups in HTML reports. This avoids a bug in earlier versions of criterion where benchmark group colors could be chosen that were almost completely white, which made them impossible to distinguish from the background.

  • Add an -fembed-data-files flag. Enabling this option will embed the data-files from criterion.cabal directly into the binary, producing a relocatable executable. (This has the downside of increasing the binary size significantly, so be warned.)

  • Fix issue where --help would display duplicate options.

  • Add a Semigroup instance for Outliers.

  • Improve the error messages that are thrown when forcing nonexistent benchmark environments.

  • Explicitly mark forceGC as deprecated. forceGC has not had any effect for several releases, and it will be removed in the next major criterion release.

  • Important bugfix: versions and were incorrectly displaying the lower and upper bounds for measured values on HTML reports.

  • Have criterion emit warnings if suspicious things happen during mustache template substitution when creating HTML reports. This can be useful when using custom templates with the --template flag.

  • Add GCStatistics, getGCStatistics, and applyGCStatistics to Criterion.Measurement. These are inteded to replace GCStats (which has been deprecated in base and will be removed in GHC 8.4), as well as getGCStats and applyGCStats, which have also been deprecated and will be removed in the next major criterion release.

  • Add new matchers for the --match flag:

    • --match pattern, which matches by searching for a given substring in benchmark paths.
    • --match ipattern, which is like --match pattern but case-insensitive.
  • Export Criterion.Main.Options.config.

  • Export Criterion.toBenchmarkable, which behaves like the Benchmarkable constructor did prior to criterion-

  • Use statistics-0.14.

  • Replace the hastache dependency with microstache.

  • Add support for per-run allocation/cleanup of the environment with perRunEnv and perRunEnvWithCleanup,

  • Add support for per-batch allocation/cleanup with perBatchEnv and perBatchEnvWithCleanup.

  • Add envWithCleanup, a variant of env with cleanup support.

  • Add the criterion-report executable, which creates reports from previously created JSON files.

  • Unicode output is now correctly printed on Windows.

  • Add Safe Haskell annotations.

  • Add --json option for writing reports in JSON rather than binary format. Also: various bugfixes related to this.

  • Use the js-jquery and js-flot libraries to substitute in JavaScript code into the default HTML report template.

  • Use the code-page library to ensure that criterion prints out Unicode characters (like ², which criterion uses in reports) in a UTF-8-compatible code page on Windows.

  • Give an explicit implementation for get in the Binary Regression instance. This should fix sporadic criterion failures with older versions of binary.

  • Use tasty instead of test-framework in the test suites.

  • Restore support for 32-bit Intel CPUs.

  • Restore build compatibilty with GHC 7.4.

  • If a benchmark uses Criterion.env in a non-lazy way, and you try to use --list to list benchmark names, you’ll now get an understandable error message instead of something cryptic.

  • We now flush stdout and stderr after printing messages, so that output is printed promptly even when piped (e.g. into a pager).

  • A new function runMode allows custom benchmarking applications to run benchmarks with control over the Mode used.

  • Added support for Linux on non-Intel CPUs.

  • This version supports GHC 8.

  • The --only-run option for benchmarks is renamed to --iters.

  • The dependency on the either package has been dropped in favour of a dependency on transformers-compat. This greatly reduces the number of packages criterion depends on. This shouldn’t affect the user-visible API.

  • The documentation claimed that environments were created only when needed, but this wasn’t implemented. (gh-76)

  • The package now compiles with GHC 7.10.

  • On Windows with a non-Unicode code page, printing results used to cause a crash. (gh-55)

  • Bump lower bound on optparse-applicative to 0.11 to handle yet more annoying API churn.

  • Added a lower bound of 0.10 on the optparse-applicative dependency, as there were major API changes between 0.9 and 0.10.