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mehen diff compares metrics between two git revisions and emits a per-file delta report. It is the engine behind the GitHub Action and the recommended way to wire mehen into a PR workflow. 
mehen diff [OPTIONS]
FlagDescription
--from <FROM>Base revision to compare from.
--to <TO>Head revision to compare to.
-p, --paths <PATHS>...Repository-relative files or directories to compare.
-M, --metrics <METRICS>Comma-separated metrics. When omitted, defaults are resolved per file language: source-code files use cyclomatic,cognitive,nom.functions,loc.lloc,mi.visual_studio; SQL files use sql.change_risk_score,sql.maintainability_index,sql.review_burden_index,sql.cognitive_complexity,sql.loc.code. An explicit list applies to every file. Prefix with + for higher-is-better, - for lower-is-better.
-I, --include <INCLUDE>...Glob to include files.
-X, --exclude <EXCLUDE>...Glob to exclude files.
-O, --output-format <OUTPUT_FORMAT>markdown or json.
--show-unchangedShow files where every metric is unchanged.
--ignore-generated[=<BOOL>]Skip files marked linguist-generated (default true).
--fail-on <FAIL_ON>Exit non-zero when named thresholds are crossed. Comma-separated: dmi-drop, new-broken-link, filler-high, all.

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Examples

mehen diff --from main --to HEAD --paths src --output-format markdown

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Output formats

GitHub-flavored Markdown table optimized for sticky PR comments. This is what the GitHub Action posts on each PR.

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What gets compared

mehen runs the equivalent of mehen metrics against each side, joins by repository-relative path, and computes per-metric deltas. Files that exist on only one side are reported as new or deleted. Files matched by linguist-generated are skipped by default. When no --metrics are given, a mixed pull request (e.g. both .ts and .sql files) produces a single table whose columns are the union of each language’s default metrics. Every row populates only the columns its analyzer publishes; columns from another language render as –. This keeps SQL changes visible in the default GitHub Action path — without it, SQL files would be measured only against source-code metrics they never emit and silently drop out as unchanged.

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--fail-on thresholds

--fail-on accepts a comma-separated list of band-crossing rule IDs:
RuleTriggers when…
dmi-dropA Markdown file’s DMI crosses a band downward.
new-broken-linkAt least one new broken link is added.
filler-highA Markdown file’s Filler / Lazy Risk is ≥ 0.60.
allAny of the above.
The rules align with the severity-1 / severity-2 indicators on the PR comment design page. For per-metric numeric gating (e.g. “fail if cyclomatic delta > 5”), use the GitHub Action’s thresholds input, which post-processes the JSON report. See Concepts → Thresholds and diffs.

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Exit codes

CodeMeaning
0Success — the comment is advisory.
1IO, git, parser-fatal, or unsupported-language error.
2One or more --fail-on rules crossed (gating exit).

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See also