21st_magic_component_builder

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

With no annotations, the description carries the burden of disclosing behavior. It states the tool only returns a snippet and does not modify files, requiring the agent to edit/add files afterward. This is honest and useful, though it doesn't cover error cases or output format details.

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 three sentences, front-loaded with the usage trigger, and every sentence serves a purpose. The 'ONLY' emphasis is efficient and no filler is present.

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?

The description covers the tool's purpose, when to use it, what it returns, and the required follow-up action (edit/add files). It lacks an explicit description of the snippet's format or error behavior, but for a simple snippet builder this is acceptable given the schema and absent output schema.

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 baseline is 3. The description itself does not add parameter-specific meaning beyond what the schema already provides, so it does not exceed the baseline.

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 builds new UI components and that it 'ONLY returns the text snippet', which differentiates it from the inspiration and refiner siblings. Trigger examples (button, input, dialog) make its scope unambiguous.

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?

It explicitly tells when to use the tool ('when the user requests a new UI component' with examples like /ui and /21st). It does not mention when not to use it or name alternatives, but the guidance is clear enough for an agent to decide.

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