The skilldrop GitHub Action
Every input and output of the skilldrop GitHub Action, what it sends to Claude and what it never runs, which skills fit CI, and what a run costs.
The repo root is a GitHub Action. For the task of adding it to a workflow, see Run a skill in CI.
What a run does
The action sends a skill's SKILL.md (with the reference files it links) to Claude as the system prompt, gives it your input, writes the answer to the job summary and a file, and can fail the step when the answer contains a verdict you name.
Nothing in the skill is executed. Skills that normally run a script (like pre-merge-review's gate) are told they can't, and reason through it by hand instead, naming the command to run. Run the script in its own step if you need its real exit code.
Requirements
- An Anthropic API key, saved as a repository secret named
ANTHROPIC_API_KEY(Settings → Secrets and variables → Actions). - Pin the action to a commit SHA, as you would any third-party action. The examples use
@mainfor readability only. diff-baseneeds a checkout withfetch-depth: 0.
Inputs
| Input | Default | What it does |
|---|---|---|
skill | required | The skill's name: doc-critique, pre-merge-review, release-notes, … |
input | — | The request text |
input-file | — | A file appended to the request, such as a generated report |
diff-base | — | A git ref; git diff <ref>...HEAD is appended. Check out with fetch-depth: 0. |
catalog | skilldrop's catalogue | Where to find the skill: a skilldrop catalogue, or any folder of <skill>/SKILL.md. Use . for skills in your own repo (.claude/skills/, .agents/skills/, skills/ and packs/ are all searched). |
model | claude-sonnet-5-5 | Any Claude model ID |
max-tokens | 8000 | Output cap |
fail-on | — | A regular expression; the step fails when the output matches |
output-file | skill-output.md | Where the output is written, for a later step to post as a PR comment or upload |
anthropic-api-key | required | Pass ${{ secrets.ANTHROPIC_API_KEY }}, never a literal |
Outputs
| Output | What it holds |
|---|---|
output-file | Path of the file holding the skill's output |
failed | true when fail-on matched |
Good fits
doc-critiqueon changed ADRs, design docs and runbooksrelease-notesondiff-base: <last tag>to draft the notes for a release PRpre-merge-reviewas an advisory second reviewer, with the real lint and test gate as its own step- Your own skills, with
catalog: .
Cost and privacy
Each run is one API call: the skill's files plus your input in, the answer out. A diff and a skill together are usually well under 50k input tokens. The input goes to the Anthropic API under your key and your organisation's data terms. Don't point it at files you couldn't send there.