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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds real behavioral detail beyond that: it fetches .well-known/agent-card.json, validates protocol compatibility, checks for a2a-x402 and AP2 extensions, and extracts skills with pricing. It omits quota/caching behavior despite the agent_id quota-tracking parameter, which keeps it below a 5.

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?

Two sentences, front-loaded with the purpose and followed by a compact enumeration of the resolution pipeline. Dense but every clause carries information; the second sentence is long but justified by the multi-step behavior it discloses.

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 an output schema present, return-value details are unnecessary, and the annotations carry the safety profile. The description covers source endpoint, validation, extension checks and skill extraction, leaving only minor gaps like error handling for unreachable or incompatible agents.

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 both parameters are already documented in the schema (target's domain-vs-URL forms, agent_id's quota role). The description's 'by domain or URL' merely echoes the target parameter, adding no syntax or format detail beyond the schema, so 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?

The description gives a specific verb+resource ('Discover and inspect an external Agent-to-Agent (A2A) node') and scopes it by domain or URL, so an agent knows exactly what the tool targets. It does not, however, differentiate itself from near-siblings such as x402.agent_card or x402.discover, which an agent might reasonably confuse it with.

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 only implied by 'Discover and inspect an external ... node'; there is no explicit when-to-use, when-not-to-use, or named alternative among the many x402/a2a siblings. The agent must infer that this is the entry point for external agent resolution from the wording alone.

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