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

Annotations already cover readOnly/openWorld/idempotent, so the bar is lower. The description adds meaningful context beyond them: zero cost ('Free'), staleness ('Not live data'), the exact timezone definition of 'yesterday' (America/Chicago), and provenance ('as declared by public sources').

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 compact sentences, front-loaded with the cost qualifier 'Free.' before the payload description and caveats. Every clause (timezone, data source, staleness) carries information; nothing is filler.

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 input schema, no output schema, and no parameters, the description carries the full explanatory burden and does so adequately: it names the change categories returned (listing, price, status) and the time window. Return-format detail (e.g. shape or pagination) is not given, but none is strictly needed.

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 no parameters, so there is no parameter semantics to document; baseline for a zero-param tool applies. 'No inputs' correctly confirms this and reinforces that no arguments need to be constructed.

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+resource: a day-old change summary of the AI model directory, covering listing, price and status changes. This clearly separates it from siblings like list_models or get_price_index, though it doesn't explicitly name an alternative. Scope ('previous calendar day', 'public sources') is unusually precise.

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?

'Free. Not live data.' implies the use case (cost-free historical aggregate vs. live/paid alternatives) but never states when to prefer it over get_model_report or get_current_conditions. Usage is inferable rather than explicit.

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