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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the tool's safety is known. The description adds valuable context beyond that: it mentions 'Uses metered access' (cost implication) and explains the responseFormat behavior (compact vs. full and backward compatibility). No contradictions with annotations.

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?

Three sentences, front-loaded with the primary action and deliverables. Every sentence adds information: the first defines the output, the second explains required/optional parameters, the third covers formatting options and alternatives. No fluff or repetition.

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 the tool's moderate complexity (3 params, output schema present, rich annotations), the description fully addresses usage, alternatives, behavior, and constraints. It even covers cost implications (metered access) and backward compatibility, making it self-sufficient for agent decision-making.

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% and each parameter has a useful description. The description adds meaning by explaining the relationship between service and endpoint ('Service is required and endpoint optionally narrows the operation') and clarifies the responseFormat default behavior ('backward-compatible default returns the full brief plus compact form'). This enriches the schema without redundancy.

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 opens with a specific verb and resource: 'Compile one callable third-party API brief,' clearly listing the included elements (base URL, auth scheme, parameters, etc.). It distinguishes itself from sibling factreason_api_schema by explicitly stating that tool is for exploring multiple endpoints, while this one is for a single call.

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?

Provides explicit guidance: 'Prefer factreason_api_schema when exploring multiple endpoints' names the alternative tool and the condition under which to use it. Also explains the optional endpoint parameter narrows the operation, clarifying common usage scenarios.

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