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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds genuinely new behavior: the call requires the person to be signed in, and calling it while signed out triggers the app's sign-in flow. That is a side effect an agent could not infer from readOnlyHint alone. It stops short of describing failure modes if sign-in is rejected.

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, each doing distinct work: what it returns, the sign-in prerequisite, and the no-mutation guarantee. The return fields are front-loaded immediately after the purpose.

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?

With an output schema present, the description needn't spell out the return shape, and it still summarizes it; annotations cover the safety profile. The only gap is what happens when the sign-in flow is declined, which is a minor omission for a read tool.

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?

There are zero parameters, so there is nothing for the description to disambiguate; the baseline applies. The description correctly avoids inventing parameter talk for a no-arg tool.

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?

The description names the exact resource (the Faxette account the person signed in with) and enumerates the returned fields: name, email, credit, and US/EU copy. No sibling tool touches account identity, so an agent can route to it unambiguously.

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?

'Use this to see which Faxette account the person signed in with' gives clear usage context, and the sign-in prerequisite is stated. No alternative tools are named, but none of the siblings overlap in purpose, so explicit exclusions are unnecessary.

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