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

Annotations only declare readOnlyHint and openWorldHint; the description adds the critical non-obvious behavior — a $0.01 USDC x402 charge and the fact that a call returns the HTTP request plus payment requirements rather than data, requiring a second paid step. Cost, payment rail, and the two-step retrieval flow are exactly the kind of context annotations cannot express.

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?

Densely front-loaded: price first, then scope and corpus, then filters, then the payment mechanics. Every clause carries information an agent needs before calling, with no filler.

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?

With no output schema and no annotations covering payment, the description correctly explains the unusual return value (an HTTP request + payment requirements) and how to complete it. What the final paid payload contains and any rate limits remain unspecified, which is a minor gap for a search tool.

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 0%, so the description must carry parameter meaning and largely does: it names all three filters, gives the type enum values (mcp|x402), and constrains limit (<=100). 'q' is not explained (what fields are matched), and the schema types limit as a string despite the numeric bound, but the compensation for 0% coverage is solid.

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 — 'One search across ~13,000 agent tools' — and quantifies the corpus (4,259 MCP servers + ~8,900 x402 APIs), so the agent knows exactly what this covers. It implicitly spans the ground of siblings mcp_servers and x402_services as a unified search, but never names or contrasts with those siblings, so differentiation must be inferred.

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?

Usage is implied rather than stated: it gives the payment precondition ('pay with any x402 client') but never says when to choose this over mcp_servers, x402_services, or apis_search. No explicit when-not guidance or alternative routing is provided.

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