dorny/paths-filter Outputs Always False - Causes & Fixes

By Daniel Zoghalchali·Latchkey

dorny/paths-filter reports every filter as false (or true) because it cannot compute the changed-file set - usually a checkout without enough history, or a base it cannot diff against.

What this error means

Downstream steps gated on steps.filter.outputs.<name> never run (or always run). The filter step succeeds but its boolean outputs do not reflect the actual file changes.

- uses: dorny/paths-filter@v3
  id: filter
# later: steps.filter.outputs.src is always 'false'
# because the diff base could not be resolved on a push event

Common causes

No base ref to diff against

On push events the action diffs against the before commit; on a force-push or first commit, or with a shallow clone lacking that ref, it cannot compute changes and returns false.

Missing step id or mismatched filter keys

Outputs are read as steps.<id>.outputs.<filter>. Without an id on the step, or with a filter name that does not match what you reference, the condition reads an empty value.

How to fix it

Give the step an id and define filters

- uses: actions/checkout@v4
- uses: dorny/paths-filter@v3
  id: filter
  with:
    filters: |
      src:
        - 'src/**'
- if: steps.filter.outputs.src == 'true'
  run: npm test

Provide a base for events without one

1. On pull_request the action diffs against the PR base automatically.
2. For push on the default branch, set base to the branch so it diffs against the prior commit.
3. Avoid overly shallow checkouts that drop the commit the diff needs.

How to prevent it

• Always give paths-filter a stable id and compare outputs to the string "true".
• Set an explicit base for push events on the default branch.
• Prefer pull_request events where the diff base is unambiguous.

Frequently asked questions

Related guides

References

• GitHub Actions documentation
• Workflow syntax for GitHub Actions