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

Annotations already declare readOnly, idempotent, and non-destructive, so the safety profile is covered. The description adds a genuine behavioral fact beyond them: this call does not kick off a verification, so the agent knows the balance read has no side effects. It stops short of noting rate limits or whether calls count against quota.

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?

One front-loaded sentence with no filler: the read action and its scope come first, and the non-verification qualifier follows immediately.

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 with annotations covering safety, the description is nearly complete. The only gap is that with no output schema, it doesn't say what the returned balance looks like (integer count, unit, or whether it is per-account), which an agent might want before surfacing the number.

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, so the baseline of 4 applies; there is nothing for the schema to document or for the description to compensate for.

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?

Names a specific verb (Read) and a specific resource (available MailerCheck verification credit balance), which is unambiguous. The clause 'without starting verification' also implicitly separates it from the verify_email sibling, though it never names that sibling.

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 phrase 'without starting verification' implies the use case (check balance without consuming a verification action), but it never explicitly states when to prefer this over mailercheck_account or mailercheck_verify_email. Usage is inferred rather than directed.

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