Building Reusable Claude Code Skills By the end of this lesson, students should be able to: What Skills are. Skills are markdown files containing instructions that Claude Code applies automatically when specific conditions are met. A Skill captures a repeatable workflow, standard, or best practice. When Claude Code detects that the current task matches a Skill's trigger conditions, it incorporates the Skill's instructions into the session without the user needing to re-enter them. Skills vs. CLAUDE.md. CLAUDE.md provides persistent project-wide context – tech stack, conventions, current focus. It is always active for sessions in that directory. Skills are task-specific instructions that activate conditionally – when Claude is doing a code review, when it is writing documentation, when it is debugging a specific error type. Skills extend CLAUDE.md with workflow-specific guidance that does not belong in a project-wide context file. | | CLAUDE.md | Skills | |–|———–|——–| | Activation | Always active for the directory | Conditionally, when trigger matches | | Scope | Project-wide context | Task-specific workflows | | Best for | Architecture, conventions, current state | Checklists, protocols, specific workflows | How Skill detection works. Claude Code reads available Skills and evaluates whether the current task context matches a Skill's trigger conditions. When a match is detected, the Skill's instructions are incorporated into Claude's context for that task. Verify current Skill detection implementation at docs.anthropic.com. Where Skills are stored. Skills are markdown files stored in a designated Skills directory. In Claude Code, Skills can be stored at user level (available in all sessions) or project level (available for a specific project). Verify current file paths and structure at docs.anthropic.com/en/docs/claude-code. A developer has a team PR review checklist that every reviewer should apply – but it is never remembered completely from memory. She creates a Skills file for "code review" that activates when Claude is asked to review code or a PR. Every Claude Code code review session now automatically includes the checklist. New team members get the same review quality from their first review without needing to memorize the checklist. The Skill replaced a "don't forget to…" section in the CLAUDE.md with a purpose-specific instruction file that activates when and only when code review happens. Skills add instructions to Claude's context automatically based on pattern matching. A poorly-specified Skill may activate in unintended contexts – adding instructions that are irrelevant or counterproductive for the actual task. Review Skill activation patterns regularly to ensure Skills are activating where intended and not where they should not. Log in and enroll to access lesson quizzes.
Lesson 1: What Skills Are and How They Work
Lesson Objectives
Lesson Content
Practical Example
Safety Notes