Describe a UI need in plain language and get ranked components — including an explicit answer when this catalog deliberately does NOT ship something and you should use the OS's own control instead. Call this before building any UI control by hand.
| Name | Required | Description | Default |
|---|---|---|---|
| need | Yes | e.g. "a progress bar for an upload" |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden of behavioral disclosure. It reveals that results are ranked and that the tool will explicitly report missing components and recommend OS-native controls. This is meaningful behavioral context, though it does not describe return shape or error behavior.
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?
Two sentences with no filler. The primary action and outcome are front-loaded, and the important fallback behavior is included efficiently. Every sentence earns its place.
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?
For a simple one-parameter tool with no output schema, the description is mostly complete. It explains what the tool does, when to call it, and the notable edge case of intentionally missing components. It could mention ranking criteria or result format, but these are minor gaps for this level of complexity.
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 coverage is 100% and the single parameter is documented with an example. The description adds the notion of 'plain language' and 'UI need,' which clarifies the expected input style, but does not significantly go beyond the schema. Baseline 3 is appropriate.
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 states a specific verb ('describe', 'get ranked components') and a clear resource (UI components), and distinguishes itself by emphasizing plain-language queries and explicit fallback answers when the catalog doesn't ship something. This clearly separates it from siblings like list_components or get_component.
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 explicitly says to call this before building any UI control by hand, giving a clear trigger condition. It does not name sibling alternatives or when-not-to-use conditions, but the context is strong enough for an agent to decide when this tool is appropriate.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.