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

Goes well beyond the readOnly/idempotent annotations: it says the call is free and consumes no credits or generations, explains the team_pool case where auto_topup is null and the owner manages it, and clarifies how credits.available is derived. These are exactly the edge behaviors an agent cannot infer from annotations.

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 dense sentences, each doing distinct work: what it returns, how to read the fields, and what it costs / where billing lives. The expensive-generation warning is front-loaded in the action-relevant position.

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 no output schema, the description carries the return-value burden and does so by defining credits.available, resets_at, team_pool, and auto_topup. For a zero-parameter read tool, an agent has everything needed to call it and interpret the result.

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 input parameters, so the baseline of 4 applies; nothing in the description is needed to explain request arguments. It does add meaning about response fields, but that value is better credited under transparency and completeness.

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 (show credit balance, plan, auto top-up settings) and scopes it tightly as a free read-only lookup. It also implicitly separates itself from siblings like getPricing by noting that purchasing credits and changing auto top-up happen in the web app, not here.

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 an explicit trigger: check this before an expensive generation instead of waiting for a 402. It also gives an explicit when-not by routing billing actions to billing_url in the web app.

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