21st_magic_component_builder

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries full burden. It discloses key behavioral traits: the tool returns text snippets (not files), and post-call actions are required (editing/adding files). However, it doesn't mention authentication needs, rate limits, error conditions, or what happens if parameters are invalid. For a 5-parameter tool with no annotations, this leaves significant behavioral gaps.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is appropriately sized with three sentences that each serve distinct purposes: when to use, what the tool does, and post-call instructions. It's front-loaded with the primary usage scenario. While efficient, the third sentence about post-call actions could be slightly more integrated with the tool's purpose.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given 5 parameters with 100% schema coverage but no annotations and no output schema, the description provides adequate context about when and how to use the tool. However, it doesn't explain what the return value looks like (only says 'text snippet' without format details) or address potential complexities like error handling. For a tool that generates code snippets, more output information would be helpful.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents all 5 parameters thoroughly. The description adds no parameter-specific information beyond what's in the schema. According to scoring rules, when schema coverage is high (>80%), the baseline is 3 even with no param info in description, which applies here.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool 'returns the text snippet for that UI component' when users request new UI components, providing a specific verb (returns) and resource (text snippet for UI component). It distinguishes from siblings by specifying this tool only returns snippets, while siblings likely handle inspiration or refinement. However, it doesn't explicitly name the sibling tools for comparison.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides explicit usage guidance: 'Use this tool when the user requests a new UI component' with concrete examples (mentions /ui, /21, /21st, or asks for specific components like button, input, etc.). It also specifies 'This tool ONLY returns the text snippet' and instructs what to do after calling ('you must edit or add files to integrate'), creating clear boundaries for when to use this tool versus other actions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.