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

Annotations only say readOnlyHint=true/openWorldHint=false, yet the description adds substantial context: it is an estimate and not a billing ceiling, actual billing follows provider-reported usage and is normally less, no key is required, and attested/private routing is quoted at the model's price on verified routes. This is exactly the kind of cost/auth behavior an agent needs beyond the structured hints.

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 with no filler; the pricing semantics are front-loaded. Slight deductions for the roundabout opening noun phrase and the repeated 'at the model's price' clause, which make it less scannable than it could be.

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 still conveys the return's essence (dual USDF/USD figures, 4096-token cap) and the pricing model. However, it does not describe the shape of the returned quote or how the two currencies relate, leaving a modest gap for a tool whose whole job is producing a structured price estimate.

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?

With 100% schema coverage the baseline is 3, but the description adds real meaning: 'Pass prompt or messages' clarifies the two mutually optional input paths, and the 'output capped at 4096 tokens' note relates to the token budget. The 4096 cap sits somewhat awkwardly next to the schema's max_tokens default/cap wording, creating mild ambiguity about which budget is meant.

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 defines the tool as 'the hold the chat tool places before running a request' and clarifies 'It is an estimate, not a ceiling', so an agent can infer this returns a pre-flight cost quote in USDF/USD for a chat request. It is distinguishable from siblings like chat, balance and receipt, though the purpose is expressed through a metaphor rather than a direct verb+resource statement.

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?

It states when this applies (before running a request, mirroring the chat flow) and gives input guidance ('Pass prompt or messages', 'No key needed'). It also names the conditions under which special routing pricing applies (attested hardware via ':private' or provider.private, Private-tier keys), but it never explicitly contrasts with an alternative tool or states when not to use it.

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