> ## Documentation Index
> Fetch the complete documentation index at: https://mehen.ophi.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Thresholds and diffs

> How `mehen diff` thresholds gate the GitHub Action.

The [GitHub Action](/guides/github-action) accepts a `thresholds` input that gates PRs on adverse
per-file metric deltas. This page explains how thresholds compose with the JSON output of
`mehen diff` and how to write your own gating logic in CI.

## Action threshold input

```yaml theme={null}
- uses: ophi-dev/mehen@v1
  with:
    paths: src
    thresholds: |
      cyclomatic=5
      cognitive=4
      loc.lloc=120
```

The action runs `mehen diff` and then evaluates each per-file delta against the supplied limits. A
violation:

* Counts toward the `violations` output.
* Fails the action when `fail-on-threshold: true` (default).

## Adverse direction

Each metric has an adverse direction. Thresholds limit how far in the adverse direction a per-file
delta is allowed to go:

| Metric             | Adverse | Example threshold                                                 |
| ------------------ | ------- | ----------------------------------------------------------------- |
| `cyclomatic`       | ↑       | `cyclomatic=5` blocks a per-file increase by more than 5.         |
| `cognitive`        | ↑       | `cognitive=4`.                                                    |
| `loc.lloc`         | ↑       | `loc.lloc=120`.                                                   |
| `mi.visual_studio` | ↓       | `mi.visual_studio=10` blocks a per-file decrease by more than 10. |
| `halstead.volume`  | ↑       | `halstead.volume=200`.                                            |

mehen knows the direction for the standard metrics and applies the threshold accordingly.

## Composition with diff JSON

If you want richer logic than the action provides, run `mehen diff -O json` yourself and pipe the JSON
into a CI script:

```bash theme={null}
mehen diff --from "$BASE_SHA" --to "$HEAD_SHA" --paths src \
           --output-format json > metrics-diff.json
jq '.files[] | select(.deltas.cyclomatic.delta > 5)' metrics-diff.json
```

`jq` and the JSON shape give you full control. The downside: you reimplement adversity rules.

## See also

* [GitHub Action](/guides/github-action) — full input/output reference.
* [Commands → diff](/commands/diff) — `mehen diff` CLI reference.
* [Output formats](/concepts/output-formats) — JSON shape.