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

Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=false, so the agent knows this mutates state but is safe to retry. The description adds one genuinely useful behavioral fact — the 15-minute expiry — but says nothing about behavior on an incorrect or expired code (attempt limits, error surface) or what the successful result looks like, which is the main remaining unknown for a verification call.

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 short sentences, no waste, with the action front-loaded and the operational constraint (expiry) immediately following. Nothing extraneous for a two-parameter 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 small, well-annotated two-parameter tool with a fully described schema, the description covers the essential scope and the time constraint. The only gap is failure-path behavior, which a verification tool ideally would mention, but it is minor given the simplicity.

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 100% and the schema already documents both parameters ('6-digit code from the email', 'Agent key from agent_register'). The description only reinforces that the code comes from agent_contact_set, adding no syntax, format, or validation detail beyond the structured fields. 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?

States a specific verb and resource ('Confirm the 6-digit code') and names the originating sibling (agent_contact_set), which cleanly separates it from agent_contact_set (which sends the code) and agent_endpoint_verify (which verifies endpoints). An agent can pick it out without opening 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?

The description establishes the precondition implicitly: this must follow agent_contact_set, and the 15-minute expiry tells the agent to act promptly. It does not explicitly state what to do on failure or whether verification is a prerequisite for other agent operations, so it stops just short of full when/when-not guidance.

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