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

Annotations already cover read-only, non-destructive and non-open-world, and the description adds traits annotations cannot express: no monthly unit spend, availability after allowance exhaustion, and that rate limiting still applies. It also implies the values are time-varying, consistent with idempotentHint=false, and outlines the returned fields.

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, zero filler: the first delivers scope and return contents, the second delivers the cost/quota/rate-limit behavior. The most decision-relevant facts are front-loaded.

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?

For a zero-parameter read with no output schema, the description supplies everything needed: what it returns, that it is free of quota cost, that it survives quota exhaustion, and that rate limits still bind.

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 the baseline is 4. The description correctly implies the account is implicit ('this account's') rather than a required argument, leaving no ambiguity an agent would need to resolve.

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 this account's usage') and enumerates exactly what is returned: plan allowance, units used and remaining, and UTC reset times. That enumeration distinguishes it from the sibling status-style tools (get_availability, get_data_status) without needing to name them.

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 clear calling context: it costs no monthly units and remains usable after the monthly allowance is exhausted, so an agent knows it is a safe diagnostic call at any time. It stops short of naming an alternative or stating when not to use it, so it is clear context without explicit exclusions.

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