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

Annotations cover the safety profile (readOnly/idempotent/openWorld), and the description adds substantial context beyond them: pricing (USD 0.005), a free-tier rate limit (10 calls/IP/UTC day), failure semantics (no samples = 404, missing store = 503, not charged), typical latency (<1 s), and an explicit untrusted-data warning. This is genuinely additive.

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 the when-to-use and return-value summary, then operations details. Dense but nearly every clause earns its place (cost, errors, untrusted data); the 'not a judgement of the service' and vantage-point caveats are slightly tangential but useful.

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?

An output schema exists, so return values need not be re-explained, and the description still covers purpose, inputs, cost, rate limits, error behavior, latency and security caveats. Nothing an agent needs to call it correctly is missing.

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% and both url and host already document the mutual-exclusion rule ('Give url or host, not both'). The description's '`url` or `host`, not both' repeats the schema rather than adding format or scope meaning, so the 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 (know if an endpoint was up) plus a precise resource and scope (one x402 endpoint/MCP server/host over 30 days). The explicit 'one ... or host' scope pairs with the sibling name get_endpoint_uptime_bulk, letting an agent distinguish them 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 a clear when-to-use trigger ('Use when an agent must know if ... was up, with a valid 402, over the last 30 days'). However it names no alternatives or exclusions (e.g. get_endpoint_history for longer windows, or check_x402_endpoint_before_paying), so routing to a sibling is left to inference.

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