Use before implementing or refactoring software when the task requires designing module boundaries, APIs, layers, abstractions, services, repositories, adapters, or architecture. Helps coding agents reduce total system complexity by creating deep modules, hiding implementation knowledge, avoiding leakage and pass-through APIs, comparing alternative designs, documenting interfaces before coding, and critiquing existing architecture.

Use when writing unit tests, integration tests, or end-to-end tests, creating mocks/stubs/fakes, designing a testing strategy, doing TDD, reviewing test quality, fixing flaky tests, or refactoring test suites. Generates risk-focused test plans, picks appropriate test levels, chooses between mocks/fakes/real dependencies, and applies Arrange-Act-Assert patterns with concrete examples.

Evidence-first mailbox triage, drafting, send verification, and sent-mail-safe follow-up workflow for ECC. Use when the user wants to organize email, draft or send through the real mail surface, or prove what landed in Sent.

Write articles, guides, blog posts, tutorials, newsletter issues, and other long-form content in a distinctive voice derived from supplied examples or brand guidance. Use when the user wants polished written content longer than a paragraph, especially when voice consistency, structure, and credibility matter.

Clean up merged branches locally and on remote, keeping only main, dev, and gh-pages.

Design multi-stage CI/CD pipelines with approval gates, security checks, and deployment orchestration. Use when architecting deployment workflows, setting up continuous delivery, or implementing GitOps practices.

MANDATORY first step before writing any code that uses a framework, library, or technology. Searches the Tessl registry for best-practice tiles and installs them before implementation begins. MUST be invoked before: building a new app or feature, writing tests, configuring CI, setting up auth, designing APIs, database work, Docker setup, linting config, or any task involving React, Express, Next.js, TypeScript patterns, Playwright, SQLite, or other technologies. Use when the user says "build", "create", "implement", "set up", "configure", "write tests", or starts any greenfield project. Do NOT use for trivial edits or renaming variables. Requires Tessl MCP tools: search and install.

Apply this skill when designing, building, or reviewing API routes, Server Actions, or data fetching patterns in a Next.js + TypeScript + Drizzle application. Triggers on requests like "create an API endpoint", "add a server action", "design the API", "add pagination", "handle this request", "validate query params", or any time you are building the boundary between client and server. Use proactively — all API design decisions should follow these patterns.