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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description goes beyond them by disclosing the authentication mechanic: the fxa_... account_key, its origin in create_account, and that it may alternatively be passed as an Authorization header. It does not say what happens when the key is omitted (the parameter defaults to an empty string).

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 with no filler, and the resource inventory is front-loaded before the credential mechanics. The parenthetical about the Authorization header is compact and useful rather than padding.

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, return values need not be detailed, and the description correctly focuses on scope and auth. The one thing missing for an agent choosing between this and get_credit is the differentiation, but nothing needed to call the tool correctly is absent.

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 description coverage is 0%, so the burden falls on the description, and it largely delivers: it names the parameter's source tool, its fxa_... format, and an alternate transport (Authorization header). It stops short of explaining the empty-string default or the behavior of an unauthenticated call, which is the only remaining gap for a single parameter.

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 enumerates exactly what the account resource contains (credit, usage, API keys, payments, top-up link), which is more specific than a restated name. However, it never distinguishes itself from the sibling get_credit or explains how the two overlap, leaving the agent to guess which to call for credit data.

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?

There is no when-to-use guidance and no exclusions; the sibling get_credit is not mentioned even though the description claims this tool also returns credit. The only routing hint is that the key originates from create_account, which is setup information rather than usage guidance.

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