A2A: List Agents

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

Goes well beyond the readOnlyHint annotation by disclosing that it reads the local card cache, makes no network calls, lists peers even if down, and explains the cached_at absence semantics. This gives the agent accurate expectations about behavior.

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 dense sentences with no filler. The primary purpose and scope are front-loaded, followed by behavioral nuance and a clear usage preference, making every sentence valuable.

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 zero-parameter read-only listing tool with no output schema, the description covers purpose, source, network behavior, and a key field semantic. Nothing essential is missing for an agent to select and invoke this correctly.

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 tool takes zero parameters and schema coverage is 100%, so there is no parameter meaning for the description to add. The description nonetheless clarifies the scope of what is listed, which is sufficient.

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 and resource: list the A2A peers this machine knows about. It enumerates the exact sources (configured peers, own daemon, discovered agents) and explicitly distinguishes itself from a2a_discover_agent by name.

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?

Includes explicit guidance to prefer this tool over discovering peers one at a time when only the set of peers is needed. Also clarifies that it makes no network calls, which signals a cheap, safe first-step choice.

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