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

With no annotations, the description carries the full burden and does so: it declares no signing, no auth, and free; explains that activity numbers are 'conservative by design, not a popularity score'; lists the flag types returned; and explicitly refuses prescriptive advice ('never tells you to block or refuse anyone'). This is unusually rich behavioral context for a read tool.

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-loads the action and the routing condition, then layers return detail. Sentences mostly earn their place, but the 'SPEC §14' citation and the long parenthetical on counting methodology add length without helping an agent decide or invoke.

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?

No output schema exists, and the description compensates by describing both the registered and unregistered return shapes in prose. It is nearly complete for a 4-param read tool, though it omits failure behavior (invalid input, no signal found at all) and per-parameter format guidance.

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 0% and the schema has no required fields or oneOf constraint, so the description's 'pass exactly one of agentId, domain, agentCardUrl, or publicKey' supplies the critical mutual-exclusivity rule and names all four parameters. It does not explain the expected format of each input (e.g., key encoding or URL form), which keeps it at a 4.

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+resource ('look up a counterparty') and its scope, plus what the return contains for both registered and unregistered agents. The framing 'BEFORE accepting an invite or offering a session' separates it from siblings like verify_agent and invite_counterparty without needing the 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?

Explicitly says when to call it (before accepting an invite or offering a session) and how to pass inputs ('exactly one of...'). It also sets interpretation boundaries ('informational — decide for yourself'). It does not name a sibling alternative or state when not to use it, so it stops 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.