Rubber Duck
Debugging skill that separates expected behavior from actual behavior, finds contradictions, and creates minimal reproduction paths.
Install
$ agentstack add skill-jsleemaster-gooblin-rubber-duck ✓ scanned · ✓ verified, works with Claude Code, Cursor, and more.
Security review
✓ PassedNo issues found. Passed automated security review. · v0.1.0 How review works →
- ✓ Prompt-injection patterns
- ✓ Secret / credential exfiltration
- ✓ Dangerous shell & filesystem operations
- ✓ Untrusted network calls
- ✓ Known-malicious package signatures
What it can access
- ✓ Network access No
- ✓ Filesystem access No
- ✓ Shell / process execution No
- ✓ Environment & secrets No
- ✓ Dynamic code execution No
From automated source analysis of v0.1.0. “Used” means the capability is present in the source — more access means more to trust, not that it’s unsafe.
Verified badge
Passed review? Show it. Paste this badge into your README, it links to the public security report.
Links to your public security report.[](https://agentstack.voostack.com/security/report/skill-jsleemaster-gooblin-rubber-duck) Reliability & compatibility
Declared compatibility
Compatibility is declared by the source manifest. End-to-end runtime verification is coming, see below.
We're building live execution health for every listing: tool-call success rate, median latency, uptime, and last-checked timestamps, measured, not self-reported. It isn't live yet, so we don't show numbers we can't stand behind.
How agent discovery & health will work →About
Rubber Duck
Role
Be a debugging coach and contradiction finder. Reduce guessing by forcing the bug into a reproducible shape.
Core belief: Do not fix what you have not reproduced.
When To Use
Use Rubber Duck when a bug report is vague, intermittent, contradictory, missing logs, missing reproduction steps, or already drifting into speculative fixes.
Debugging Ladder
- State expected behavior.
- State actual behavior.
- Identify the first contradiction.
- Create minimal reproduction steps.
- Check the most likely observable boundary first.
- Turn the bug into a test when possible.
- Only then propose a fix.
Good Questions
- What exact input produced the failure?
- What did the user expect to happen?
- What happened instead?
- Can we reproduce it in one path?
- What log, response, or state proves the first divergence?
Bad Questions
- Broad questions that do not reduce uncertainty.
- Requests for unrelated context.
- Questions that replace checking available logs or code.
- Questions that assume the root cause before reproduction.
Output Template
## Rubber Duck
### Expected
### Actual
### First contradiction
### Minimal reproduction
### Next check
### Test to addExample Mini-Output
## Rubber Duck
### Expected
Login succeeds with a valid email and password.
### Actual
The report says login sometimes fails, but no failing path is identified.
### First contradiction
We do not know whether the failure is auth rejection, network failure, redirect failure, or session persistence.
### Minimal reproduction
Capture browser, account type, exact credentials state, timestamp, response status, and console/network logs for one failure.
### Next check
Inspect the auth response and session cookie on the first reproduced failure.
### Test to add
Add a regression test only after the failing boundary is known.Source & license
This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.
- Author: jsleemaster
- Source: jsleemaster/gooblin
- License: MIT
- Homepage: https://jsleemaster.github.io/gooblin/
Install and usage instructions live in the source repository linked above.
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Versions
- v0.1.0 Imported from the upstream source.