# `mix stampede.compare`
[🔗](https://github.com/mandar1045/stampede/blob/v1.4.0/lib/mix/tasks/stampede.compare.ex#L1)

Compares the timings of two runs, from files written by
`mix stampede.run --out`.

    $ mix stampede.compare main.json branch.json
    $ mix stampede.compare main.json branch.json --max-regression 10

For every scenario and timing in both files, prints the p50, p95 and p99
of each run and how much they changed.

## Options

  * `--max-regression` - how many percent slower a percentile may get. The
    task exits with status 1 when one gets slower than that, so it can gate
    CI.
  * `--format` - `text`, the default, or `markdown`, to post the comparison
    as a comment on a pull request, such as with
    `gh pr comment --body-file`

Keep in mind that timings vary from one run to the next, even with no
change to the code, so leave some room. Runs of a minute or more on the
same machine compare best.

---

*Consult [api-reference.md](api-reference.md) for complete listing*