> ## 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.

# Hotspot

> Cognitive complexity × commit frequency — files that are both fragile and frequently touched.

A **hotspot** is a file where complexity and change frequency *overlap*: complicated code that the
team also touches all the time. That intersection is the highest-leverage refactoring target —
CodeScene reports that top hotspots typically occupy \~5% of a codebase yet absorb \~18% of
development effort and \~23% of fixed defects. Complexity alone over-flags stable legacy code
nobody touches; frequency alone flags churning-but-trivial files; the product flags what actually
costs money.

## What mehen emits

| Key               | Type  | Description                                 |
| ----------------- | ----- | ------------------------------------------- |
| `history.hotspot` | float | `cognitive.sum × history.commit_frequency`. |

`history.hotspot` is one of the **default [`mehen diff`](/commands/diff) columns**.

## Better than the classic form

The open hotspot definition from the literature uses **LOC** as its complexity proxy because
that's what a history-mining tool can compute without parsing code. mehen has real parsers, so it
upgrades the proxy to [cognitive complexity](/metrics/code/cognitive) summed over the file — a
measure of how hard the code actually is to understand, not merely how long it is. The complexity
input is family-aware: SQL files use `sql.cognitive_complexity` and Markdown files use their own
cognitive-load measure, so hotspots aren't degenerate outside the shared source-code suite.

Note that CodeScene's *prioritization and ranking layer* on top of this signal is proprietary and
probabilistic; mehen deliberately implements only the open, reproducible
complexity-times-frequency overlap.

## How to read it

| Signal                             | Interpretation                                                                                                            |
| ---------------------------------- | ------------------------------------------------------------------------------------------------------------------------- |
| High hotspot, rising in a diff     | You are adding complexity to a file the team constantly revisits — the strongest refactoring signal this family produces. |
| High complexity, hotspot near zero | Complex but stable — usually not worth proactive refactoring.                                                             |
| Hotspot dropping in a diff         | A refactor is paying off exactly where it matters.                                                                        |

## References

* Tornhill, A. (2018). *Software Design X-Rays.* Pragmatic Bookshelf.
* [CodeScene hotspots documentation](https://codescene.io/docs/guides/technical/hotspots.html).

## See also

* [Cognitive complexity](/metrics/code/cognitive) — the complexity input.
* [Commit frequency](/metrics/history/commit-frequency) — the change-frequency input.