JsonReporter

JsonReporter writes results to a .json file as a structured object. It is part of the core NBenchmark package (uses System.Text.Json with no additional dependencies).

JSON output is suitable for CI dashboards, performance tracking over time, or any tooling that consumes structured data.

Setup

using NBenchmark.Reporters;

// Default - writes to the current directory
.WithReporter(new JsonReporter())

// Explicit output directory
.WithReporter(new JsonReporter("results/"))

JsonReporter takes an output directory, not a file path. It creates a uniquely named file inside that directory on each run (see File naming below).

NOTE

JsonReporter automatically creates the output directory if it does not exist. This is different from MarkdownReporter and CsvReporter, which require the directory to exist.

Output format

{
  "generatedAt": "2026-06-06T03:40:00.000Z",
  "results": [
    {
      "name": "Compute",
      "description": null,
      "mean": 275.3,
      "median": 300.0,
      "p95": 500.0,
      "p99": 500.0,
      "min": 200.0,
      "max": 1100.0,
      "standardDeviation": 85.9,
      "standardError": 6.1,
      "marginOfError": 16.2,
      "confidenceLevel": 0.95,
      "coefficientOfVariation": 0.3122,
      "confidenceIntervalLower": 259.1,
      "confidenceIntervalUpper": 291.5,
      "meanAllocatedBytes": null,
      "pValue": 0.0012,
      "isSignificant": true,
      "errored": false,
      "errorMessage": null,
      "measuredIterations": 190,
      "warmupIterations": 25,
      "runAt": "2026-06-06T03:40:00.000Z",
      "totalDuration": "00:00:00.050",
      "measuredDuration": "00:00:00.040",
      "isBaseline": false,
      "outlierMode": "removeTop5Percent"
    }
  ]
}

All timing values are in nanoseconds. Property names use camelCase.

totalDuration is end-to-end wall-clock (warmup + pre-measure GC + measured loop); measuredDuration is the measured loop only. measuredDuration <= totalDuration always; the gap is dominated by warmup iterations and the pre-measure GC.Collect.

File naming

Each call to ReportAsync writes a new file to prevent overwriting previous runs:

benchmarks-20260606-034000-001.json

The filename includes the UTC timestamp and a counter so multiple suites running in the same process do not collide.

Notes

• The output directory is created automatically if it does not exist.
• BenchmarkResult is serialised with all properties, including ConfidenceIntervalLower and ConfidenceIntervalUpper (computed from Mean ± MarginOfError).

Using with Benchmark (Quick mode)

var result = Benchmark.Run(() => MyMethod());
await result.ToJsonAsync("results/");

CLI usage (BenchmarkHost)

dotnet run -- --reporter json
dotnet run -- --reporter json --output ./results