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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=true, so the safety profile is covered and the bar is lower. The description adds real context: it maps the returned fields to their meaning and explicitly gives the unit (bytes) for account_size and max_account_size, which matters for interpreting the values. It omits auth/scope requirements and any rate-limit or caching behavior, so not a 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?

A single front-loaded sentence that puts the resource and its fields first, with no filler. The trailing endpoint reference 'GET /v1/credits/retrieve.' is the only low-value element - it restates the tool's purpose without adding decision-relevant information.

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?

There is no output schema, so the description's field list effectively serves as the return contract, and it names each field plus units - strong compensation. Minor gaps remain: it doesn't say what values appear when no paid plan or no subscription exists, and doesn't describe units for the credit quantity.

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, which is the baseline-4 case; there is nothing for the description to compensate for. The description correctly implies a pure account-scoped fetch with no filtering inputs.

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 retrieval and enumerates exactly what it returns: remaining credits, expiration (validuntil), plan/subscription, paid status, and storage used vs max in bytes. That is concrete and distinguishable from every sibling (documents, contacts, users, templates). It does not explicitly name a sibling it replaces, which keeps it out of 5 territory for a no-arg resource fetch.

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?

Usage is implied rather than stated - an agent can infer this is the account-level billing/quota lookup, and no sibling covers credits or storage, so there is no real alternative to disambiguate. No guidance on when to call it (e.g., before uploads to check quota) or on freshness/caching of the figures.

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