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

With no annotations, the description carries the burden and does disclose important behavior: it is a paid x402 call at $0.01 USDC on eip155:8453, and it validates fields, skills, interfaces, auth, signature, and reachability. It stops short of explicitly stating read-only/no-side-effects, timeout behavior, or rate limits.

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?

The description is compact and front-loaded: payment metadata, core action, validation scope, and output summary all appear without filler. Every clause contributes to selecting or using the tool.

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?

For a one-parameter validation tool with no output schema, the description is largely complete: it names the card versions, validation dimensions, and the 0-100 score plus issues result. It could be slightly more complete by explicitly stating read-only behavior and what the issues output contains.

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?

The single required parameter is fully documented in the schema, including that it accepts a base/domain URL or direct card URL. The description does not add parameter syntax or edge-case meaning beyond the schema, so the baseline of 3 is appropriate.

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 uses a specific verb and resource: 'Fetch and validate a peer agent's A2A Agent Card (v1.0 / v0.3)'. It also enumerates the validated aspects and the output, making it clearly distinguishable from siblings like mcp_probe or x402_probe.

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?

It implies the tool is for checking A2A Agent Cards, but gives no explicit when-to-use guidance, prerequisites, exclusions, or alternatives. An agent must infer when this is preferable to sibling probing or verification tools.

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