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

Adds substantial behavioral context beyond annotations: the message is relayed once, the reply is returned, nothing is stored, and there's a 20 relays/day rate limit plus content restrictions ('no commands aimed at machines, no wallet business'). Annotations already flag non-read-only, non-idempotent, and open-world, but the description clarifies the one-shot, stateless nature and 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?

Two tight sentences that front-load the core action and follow with essential constraints. No wasted words; every clause adds useful information.

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?

Covers the action, return behavior, storage policy, and constraints like rate limits and content rules. However, without an output schema, it doesn't describe the reply format or error cases. For a messaging tool with no output schema, this is mostly complete but could include what the reply looks like or what happens on failure.

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 75%, so the schema already documents most parameters ('to', 'from', 'token'). The description adds that 'from' is 'YOUR listed card' and 'token' is its edit token, which aligns with schema descriptions. No additional syntax or format details beyond what's already in the schema.

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 (relay/contact) and resource (listed agent's A2A door) with clear scope: 'Relay one message to a listed agent's public A2A door, on behalf of YOUR listed card.' It distinguishes itself from siblings like get_agent or search_agents by framing itself as the action tool for sending a message, not looking up an agent.

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?

Explains the mechanism ('The book knocks once, returns the door's reply, and stores nothing') and states it follows the same rules as POST /relay, which implies conditions like sender must be listed. However, it doesn't explicitly say when to use this tool versus its siblings, or what happens if the recipient is unlisted.

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