production-quality

name	production-quality
description	This skill should be used when preparing code for production, running "mix precommit", "mix compile --warnings-as-errors", "mix credo --strict", "mix format", "mix test", adding typespecs, evaluating security posture, checking migration safety, or reviewing code before committing

Production Quality

Overview

Production readiness is an escalation ladder — L0 (compiles) through L7 (documented). Most features should reach at least L3 before merge.

Escalation Ladder

Level	Gate	Command/Check
L0	Compiles cleanly	mix compile --warnings-as-errors (includes set-theoretic type checks on 1.18+)
L1	Formatted	mix format (with Styler)
L2	Static analysis	mix credo --strict
L3	Tested	mix test — all ok/error paths, edge cases
L4	Typed	@spec on every public function, concrete types (compiler infers many types on 1.18+, specs remain valuable for API documentation)
L5	Secure	OWASP defenses: parameterized queries, escaped output, changeset validation
L6	Observable	Telemetry on all 4 layers (OS/VM, framework, app, user)
L7	Documented	@moduledoc, @doc with examples, "why" comments

Precommit gate (L0-L3 automated):

# mix.exs aliases
precommit: ["compile --warnings-as-errors", "deps.unlock --unused", "format", "credo --strict", "test"]

Common Mistakes

• Skipping L2 (static analysis): Credo catches naming issues, long functions, and anti-patterns that code review misses
• Treating L6 (observability) as optional: You can't fix what you can't see — add telemetry before production, not after the first incident
• Unsafe migrations: Adding indexes or changing column types without concurrently: true or multi-step deployment causes downtime
• Silent error handling: 92% of catastrophic failures come from incorrect error handling — test every {:error, _} branch
• Zombie metrics: Metrics nobody acts on are waste. If it can't drive a decision, delete it

Reference Files

Read the file that matches your current problem:

• escalation-ladder.md — When: Need details on any production readiness level (L0-L7). Full Production Readiness Ladder (L0-L7 with code examples, gate criteria)
• testing.md — When: Designing test strategy or setting up TDD workflow. Testing strategy, TDD, error handling imperative, documentation standards
• property-based-testing.md — When: Testing with StreamData generators or properties. StreamData generators, custom generators, property patterns (roundtrip, idempotency, oracle, metamorphic), shrinking, Ecto integration
• security.md — When: Hardening against injection, XSS, CSRF, or managing secrets. SQL injection, XSS, CSRF, input validation, secrets management, timing attacks, magic link auth
• observability.md — When: Adding telemetry, tracing, or alerting. Telemetry layers, span conventions, tracing-as-analytics, alerting, gray failures, degraded mode, process labels
• database.md — When: Writing migrations or tuning Ecto queries. Safe Ecto migrations, isolation level warnings, dependency SLAs, performance guidelines
• ecto-preloading.md — When: Fixing N+1 queries or choosing preload strategy. N+1 detection and prevention, preload strategies (join, subquery, inline), LiveView preloading
• error-handling.md — When: Designing error flows or debugging crash patterns. Crash early patterns, strict-then-loosen, complexity analysis
• deployment.md — When: Building releases, health checks, or Docker configs. Mix releases, health checks (liveness/readiness), graceful shutdown, Docker, Fly.io/K8s patterns
• configuration.md — When: Choosing between compile-time and runtime config. config.exs vs runtime.exs, compile_env vs get_env, runtime secrets, config providers

Commands

• /precommit — Enforces L0-L3 automatically (compile, format, credo, test)
• /review [file] — Comprehensive review against L4-L7 standards
• /spike-migrate — Upgrade SPIKE code to production quality

Related Skills

• elixir-patterns: GenServer, Supervisor, OTP patterns
• cognitive-complexity: Ousterhout principles, deep modules, reducing complexity
• performance-analyzer: Benchmarking, profiling, latency analysis
• enforcing-precommit: Iron law enforcement for precommit before commits