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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context beyond annotations: it discloses that the tool charges 0.0001 XNO via x402, which is a critical side effect not captured by the annotations. It also describes the return content (settlement rails, prices, x402 health). This is strong additional transparency, though it could have elaborated on what 'x402 health' means or whether the charge applies even on failed searches.

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, each earning its place: the first states the core function and return value, the second gives a concrete filter example, and the third discloses the cost. The most important information is front-loaded. No filler or repetition of schema details.

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?

The tool has an output schema, so return values are already structured. The description covers the key contextual facts: what it searches, what it returns, the optional filter, and the cost. The only minor gap is that it doesn't explain what 'x402 health' means or whether the 0.0001 XNO charge is always incurred, but given the output schema and annotations, this is reasonably complete.

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 the schema already documents all three parameters well. The description adds a bit of semantic context by explaining the filter_rail='nano' behavior and the natural-language nature of q, but it doesn't go beyond what the schema already says. Baseline 3 is appropriate because the schema carries the heavy lifting.

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 ('Search'), a specific resource ('paid MCP and x402 service directories'), and the purpose ('for a task'). It also names the return value ('matching services with their settlement rails, prices, and x402 health'), which distinguishes it from sibling tools like web_search or check_url_status. The optional filter_rail='nano' detail further clarifies scope.

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 clearly implies when to use this tool: when the agent needs to find a paid MCP or x402 service for a task. It also gives a concrete usage example ('filter_rail='nano' shows only XNO-settling services'). However, it does not explicitly state when NOT to use it or name alternatives like web_search for general web queries, so it falls just short of a 5.

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