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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds materially more: the call is free, requires no API key, and crucially does NOT consume the keyless 10-calls-per-day allowance, though it is still subject to the per-minute pace limit. That metering nuance is exactly the kind of non-obvious behavior an agent needs and cannot infer from structured 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?

Front-loaded with the trigger phrase and the cost facts, then a single dense sentence enumerating return fields. It loses a point for redundancy: 'Cost: free' appears twice (once as 'COST: free', again as a trailing 'Cost: free' line) and 'Never charges anything' restates the same idea a third time.

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 carries the return-value burden itself — and it does, listing every notable field including resets_at and credits for agent keys. Combined with the zero-parameter schema and full annotation coverage, an agent has everything needed to call this correctly 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?

The tool takes zero parameters, so there is nothing to disambiguate; baseline is 4. The description correctly implies no inputs are required by presenting the call as unconditional.

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 ('get usage') and enumerates exactly what comes back: tier, calls used/remaining per window, credits for agent keys, resets_at, and per-minute pace limit. It also frames the user intent it answers ('how many calls or credits do I have left'), so an agent can match it to a query without opening the schema.

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?

'START HERE for ...' gives an explicit entry-point trigger for quota questions. No alternatives are named, but the sibling tools are all unrelated domains (funds, LPs, changes), so there is no real overlap to disambiguate against — the only gap is the absence of a stated when-not, which matters little here.

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