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

Consistent with readOnlyHint=true and openWorldHint=false, and adds real behavioral context the annotations cannot: prices are dated snapshots from provider pages, public read with no auth, and unknown models return UNPRICED rather than $0 — a critical anti-hallucination detail.

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-loads what the tool does, then behavior, then mode examples — easy to scan. Slight redundancy between the rate enumeration in paragraph one and the example in paragraph two, but every sentence carries 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?

No output schema exists, and the description compensates by describing the returned rates, the checked date, the source page, and the cost breakdown. Combined with the UNPRICED sentinel and no-auth note, an agent has everything needed to call and interpret results.

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 only 29% schema coverage across 7 params, the description carries the burden well: it explains that model IDs are provider-specific strings, that token counts produce a cost breakdown, and enumerates the cache-write/read and fast-mode rates. It does not separately define cache_write_5m vs cache_write_1h or the `fast` flag, leaving small gaps.

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 ('looks up') and resource ('what an AI model or an agent session costs at list price'), plus clarifies the pricing basis (dated, copied from provider pages). No sibling tool covers pricing, so there is no ambiguity to resolve.

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?

Explicitly describes two modes: no args lists all priced models and checked dates, and supplying token counts yields an exact call/session cost. It gives a concrete invocation example, though it never states when *not* to use it or a boundary (e.g. non-list/negotiated pricing).

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