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

Annotations already declare readOnlyHint=true and idempotentHint=true, so 'It changes nothing' is largely redundant. The genuinely additive disclosure is that calling it while unauthenticated triggers a sign-in flow — a side effect an agent cannot infer from the annotations, and one that explains why a read-only call might produce a prompt.

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 short sentences, front-loaded with the purpose, then the prerequisite, then the safety note. Every sentence carries distinct information; no filler or restatement of the title.

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?

An output schema exists, so return values needn't be spelled out, and the one non-obvious behavioral wrinkle (auth requirement and sign-in prompting) is covered explicitly. For a zero-parameter read tool this is complete enough to call correctly on the first try.

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 there is no parameter semantics to document; baseline 4 applies. The description correctly says nothing about inputs and instead spends its words on behavior.

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 ('see which Faxette account the person signed in with') and enumerates the returned fields: name, email, credit, and US/EU copy. This is unambiguously distinct from the fax/document siblings (send_fax, get_faxes, create_document), which all operate on fax artifacts rather than the signed-in account.

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?

Gives a clear triggering condition ('Use this to see which Faxette account...') plus a prerequisite: the person must be signed in to Faxette. No explicit exclusions or named alternatives, but the sibling set contains no competing account-inspection tool, so nothing is left ambiguous.

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