Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add oliver-kriska/claude-elixir-phoenix --skill phx-challengegit clone --depth 1 https://github.com/oliver-kriska/claude-elixir-phoenixWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/oliver-kriska/claude-elixir-phoenix/phx-challenge)<a href="https://agentmods.dev/skills/oliver-kriska/claude-elixir-phoenix/phx-challenge"><img src="https://agentmods.dev/badge/skills/oliver-kriska/claude-elixir-phoenix/phx-challenge/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/oliver-kriska/claude-elixir-phoenix/phx-challenge"><img src="https://agentmods.dev/badge/skills/oliver-kriska/claude-elixir-phoenix/phx-challenge.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00037 | $0.01102 |
| Opus 5 | $0.00018 | $0.00551 |
| Sonnet 5 | $0.00007 | $0.00220 |
| Haiku 4.5 | $0.00004 | $0.00110 |
Grade A, and why
phx-challenge scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
This is a copy
91% identical to challenge — 18 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 150 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Challenge Mode Reviews
Rigorous, critical review patterns inspired by Boris Cherny's "Grill me" approach. Push beyond first solutions to ensure quality.
Iron Laws - Never Violate These
- No approval without verification - Don't approve until all concerns addressed
- Assume bugs exist - Look for edge cases, race conditions, missing handlers
- Question everything - Even "obvious" code can hide issues
- Demand proof - Ask for tests, show state transitions, verify behavior
Adversarial Lenses (Apply to ALL Modes)
- "What Would Break This?" — Production failure modes under load, during deploys, with unexpected data
- "Assumption Stress Test" — List every assumption; which are most fragile?
- "Contradictions Finder" — Find contradictions between tests/implementation, docs/behavior, or within the changeset
Challenge Modes
Ecto Challenge (phx-challenge ecto)
Grill the developer on database changes:
Migration Safety
- Will this migration lock the table in production?
- What happens to existing records without the new field?
- Is the migration reversible?
- Are there any unsafe operations (column removal, type change)?
Query Performance
- Have you introduced any N+1 queries?
- Are there missing indexes for new WHERE clauses?
- Will this query scale with data growth?
Schema Integrity
- Are all constraints enforced at database level?
- What happens during rolling deployment (old code, new schema)?
- Are foreign key cascades correct?
Backward Compatibility
- Will old code work during deployment?
- Are there any breaking changes to the context API?
LiveView Challenge (phx-challenge liveview)
Prove the LiveView handles all cases:
Event Coverage
- List every
handle_eventclause and expected socket state - What happens if socket assigns are missing when event fires?
- Are there race conditions between user events and server pushes?
PubSub Handling
- List every
handle_infoclause and when it's triggered - Do all PubSub subscriptions have corresponding handlers?
- What happens if a message arrives before mount completes?
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 6d ago First seen · 150 lines · 37 tokens per session scan A 7e3f13046feb
phx-challenge is a skill published in the GitHub repository oliver-kriska/claude-elixir-phoenix (542 stars, last pushed 4d ago), licensed MIT. It adds 37 tokens to every session and 1,102 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 91% identical to challenge, differing in 18 lines, and is treated as a copy.
Other skills, from other repositories
skeptical-triage
Reusable 3-round self-challenge + arbiter pattern for filtering false positives from findings/verdicts. Use when the cost of a false-positive gate block exceeds the cost of 4 extra LLM turns.
anti-patterns
Catalogue of known SDLC anti-patterns that greatcto agents must actively reject when reviewing architecture, plans, code, or post-mortems. Used by architect (pre-impl), pm (planning), senior-dev (impl), l3-support (post-incident).
observability-baseline
Scaffold-time observability so a shipped product is not blind in prod from day one — error capture (Sentry), request-id structured logging, and /healthz + /readyz endpoints. stack-baseline pins Sentry but nothing wires it; this is the wiring. Loaded by app-scaffolder (bake into the scaffold), infra-provisioner (prod…
cleanup
Review and clean up the given file(s)/folder(s)/module(s): rate organization, find dead code, duplication, coupling, over-engineering, deep nesting, structural issues, and bad comments, then produce and execute a phased refactor plan. Trigger on "clean up X", "review and refactor X", "rate the code in X", "code…
rubber-ducky
Use when you've planned a non-trivial change and are about to implement it, finished a complex or multi-file piece of work, just wrote tests, or are stuck on repeated failures — and any time the user says "rubber duck this", "rubber ducky", "get a second opinion", "sanity-check my plan", "poke holes in this", "what am…
mobile-flows-maestro
This skill should be used when Maestro is explicitly requested or already present and the task is to author, run, or debug iOS/Android Maestro flows; use Maestro MCP; or handle Maestro selectors, system UI, permissions, Keychain, JavaScript, waits, device state, flakiness, or CI. Evidence includes a .maestro directory…