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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety bar is low. The description adds genuinely new context the annotations cannot convey: 'No account or spend' tells the agent there is no cost or login prerequisite, and the confirm/fallback rule describes behavior on ambiguous input.

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 short sentences, front-loaded with the core action and free of filler. Every sentence either defines the input, the cost profile, or the next step.

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?

An output schema exists, so return values need not be explained, and the description already signals the output is a plate. Combined with the fallback guidance, it covers what an agent needs to invoke this single-parameter tool correctly; only input size limits are left to the schema.

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?

Schema description coverage is 0%, so the description must carry the burden; it does map the three accepted forms (typed plate, car photo data URL, supported advert URL) onto the discriminated union and hints that only 'supported' advert URLs work. It omits constraints the schema enforces silently, such as the 16-char plate limit and the 5.6 MB photo payload cap, so it only partially compensates.

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 ('Resolve a typed plate, car photo data URL or supported advert URL') and narrows the outcome ('to a plate only'). It is clearly distinguishable from siblings like decode_plate and full_report without opening any 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?

Gives an explicit fallback workflow ('If uncertain, ask the user to confirm; if unavailable, ask for the typed plate') and routes to the next tool ('Then use free_check'). It stops short of stating when this tool should NOT be used versus alternatives such as decode_plate, so it is strong but not complete.

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