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

Beyond the annotations (which already cover readOnly/idempotent/openWorld), the description discloses cost ($0.005 per call via x402, USDC on Base), the rail restriction (MCP payments Base only), the no-results-is-free rule, the no-paid-ranking/no-custody policy, and the key safety warning that returned content is untrusted third-party data. That is substantial behavioral context an agent cannot get from structured fields.

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?

Front-loaded with purpose and usage, then parameters, then behavior, then price; each block is dense and mostly load-bearing. It is on the long side and the "No paid ranking; we hold no funds" sentence is partly promotional, but it carries trust-relevant information.

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, the description compensates by summarizing the return shape (ranked offers with price, rails, health, and a direct-pay buy plan) and covers cost, payment constraints, safety, and failure semantics. An agent has everything needed to call it and interpret results.

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%, so the parameters are already documented, and the description's recital of q/n/kind/rail/max_price/min_health adds little. It does add the transport method (GET) and the top-3 live re-check behavior, but its rail enumeration (base/solana) is narrower than the schema's full set (xrpl, evm, polygon, CAIP-2), so baseline 3 is warranted.

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 and resource ("Find x402 APIs: agent marketplace search") and scopes it to paid x402 APIs for a task. It does not, however, explicitly distinguish itself from nearby siblings such as bazaar_check, x402_check, or market_quote, so an agent must infer the boundary.

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?

"Use to find a paid x402 API for a task" gives a clear triggering context, and the pricing/rail notes implicitly bound when it applies. It stops short of stating when NOT to use it or naming an alternative tool for non-x402 search.

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