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Skills are not "called" by users, but rather Claude autonomously decides "whether to use" them. Understanding this trigger mechanism can help you write Skills that are more likely to be accurately triggered. * * * ## How the Trigger Mechanism Works When Claude starts, it loads all available Skills' names and descriptions into the context. After the user sends a message, Claude judges: Do I need to reference a Skill for this task? There's only one criterion: **the Skill's description field**. > The body of SKILL.md does not participate in trigger judgment. Claude only reads the body content after deciding to use a particular Skill. ### Trigger Flow Diagram !(https://example.com/wp-content/uploads/2026/05/a7a25224-e5fe-4591-b8b8-a52479987b3e.webp) * * * ## What Types of Tasks Trigger Skills Not all requests that match the description will trigger a Skill. Claude has an intrinsic judgment: Is this task complex enough to require specialized instructions? | Request Type | Example | Triggers Skill | Reason | | --- | --- | --- | --- | | Simple single-step task | "Read this PDF" | Usually doesn't trigger | Claude handling it directly is more efficient | | Complex multi-step task | "Extract tables from PDF and convert to Excel" | Triggers | Requires specialized workflow | | Professional domain operation | "Merge three PDFs and add watermarks" | Triggers | Involves specific toolchain | | Output has explicit format requirements | "Generate a Word report matching our company template" | Triggers | Requires specific format specifications | > If your Skills are rarely triggered, it's usually because the task description is too simple, or the description isn't precise enough. When testing, use complex, specific user requests. * * * ## Trigger Strategies for Description The description is the sole basis for triggering, and how it's written directly determines trigger accuracy. ### Strategy One: Enumerate Specific Scenarios Don't just write "what this Skill does," but also write "in what situations it should be used." # Not recommended: only describes functionality description: Handle Excel files. # Recommended: describes functionality + trigger scenarios description: > Handle Excel and CSV files, including: reading data, cleaning formats, generating charts, calculating statistical indicators, merging multiple tables. When users mention Excel, xlsx, CSV, tabular data, data cleaning, or financial reports, this Skill should be prioritized. ### Strategy Two: Use "Push" Language The Skills system naturally tends to "trigger less." Adding push language in the description can improve trigger rates. description: > Generate professional PowerPoint presentations. When users need to create slides, PPT, speeches, or reporting materials, this Skill must be used, even if the user didn't explicitly say "use pptx format". Any creation or modification of presentation documents should trigger this Skill. ### Strategy Three: List Keywords Adding a list of trigger keywords at the end of the description is a simple and effective supplementary method. description: > Code review assistant, analyzes code quality, discovers potential bugs, provides improvement suggestions. Keywords: code review, code analysis, bug checking, refactoring suggestions, code quality, static analysis. * * * ## Trigger Conflicts: Multiple Skills Match Simultaneously When a user's request could match multiple Skills, Claude will select the most relevant one based on the match degree. To avoid conflicts, you need to keep different Skills' descriptions with clear boundaries. | Conflict Scenario | Solution | | --- | --- | | Two Skills both handle PDFs | Distinguish specific operations in description, e.g., "PDF creation" vs "PDF reading" | | General Skill overlaps with specialized Skill | The specialized Skill's description should explicitly state scenarios that differentiate it from the general Skill | | Two similar Skills with similar functionality | Consider merging into one Skill and handling different situations through internal branching | > A Skill's description should "exclusively" describe its applicable scenarios, not just describe what it "can do." What it can do ≠ when it should be used. * * * ## Use Description Optimization Tool to Test Triggers The skill-creator Skill provides a description optimization script that can automatically evaluate trigger accuracy. ## Example # Run description optimization loop # --eval-set: test case file path # --skill-path: path to the Skill to optimize # --max-iterations: maximum number of iterations python -m scripts.run_loop \ --eval-set evals/trigger-eval.json \ --skill-path my-skill/ \ --model claude-sonnet-4-20250514 \ --max-iterations 5 \ --verbose The script will automatically run tests, evaluate scores, modify the description, and output the optimal result. For detailed description optimization methods, see Article 24: (https://example.com/skills/skills-description-optimize.html).