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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds only that results are 'structured agent data' and hints at filter semantics; it does not mention result caps, pagination, or empty-result behavior beyond what the schema's limit field already says.

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 short sentences, front-loaded with the core action, then the return value, then the filter usage. The 'Returns structured agent data' sentence is mildly redundant given an output schema exists, but it still sets expectations quickly.

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 an eight-parameter, zero-required search tool with a full output schema and rich annotations, the description covers the filter surface and the search-vs-fetch distinction adequately. Only marginal gaps remain (no-result behavior, result cap of 20, no pointer to get_agent for detail lookup).

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 all eight parameters (including the nuanced agent_type examples and mcp role values) are already documented in the schema. The description only restates the filter list and one mcp=server example, adding essentially no syntax or format detail beyond structured data – baseline 3 applies.

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?

States a specific verb and resource ('Search the AI Agent Index for agents') plus the return shape ('structured agent data'), and implicitly separates itself from the singular get_agent / get_agency siblings by framing it as criteria-based search. An agent can tell it apart from its siblings without opening a schema.

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?

Gives clear context for use by enumerating the filter dimensions (category, sub-type, pricing, integration, capability, MCP role) and even clarifies the mcp=server semantics. It stops short of naming the alternative route (use get_agent once you know the ID) or stating when not to search, so no explicit exclusion.

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