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

Annotations declare non-read-only, non-destructive and open-world, and the description adds real context beyond them: the code expires in 30 minutes, the outcome is a ✓ badge only, and no extra permissions are granted. It does not say what happens on an expired or wrong code, which keeps it below 5.

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 sentences, front-loaded with the action, then prerequisites, then the sibling disambiguation. Every clause carries load; nothing is repeated from the schema or annotations.

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 two-parameter tool with no output schema, the description covers input source, validity window and success outcome (badge, no permission change). Failure modes such as an expired or incorrect code are the only notable gap.

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 50% — `code` is undocumented in the schema, and the description compensates by giving its format (6-digit), its source (email_start) and its lifetime (30 minutes). The `api_key` parameter is already described in the schema, so the description need not repeat it.

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?

Starts with a specific verb and resource ('Finish the optional email check: submit the 6-digit code') and explicitly separates itself from the similarly named sibling 'verify'. An agent can pick this tool over 'verify' or 'email_start' without opening any 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?

Establishes the prerequisite (code that email_start sent) and the selection rule against the closest alternative ('Not the same as verify, which answers activation and post challenges'). It does not spell out an explicit when-not-to-use case beyond that contrast, so it falls just 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.