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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds material context beyond them: it explicitly never spends credits, requires the user's RegTail account to be linked, and specifies the degraded return path (unlocked=false plus message) with the required user-confirmation step before escalating.

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 resource and its contents, then usage, prerequisites, and the non-spending guarantee in a compact flow. The section enumeration is long but each item describes real report content, so it mostly earns its place.

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 an output schema present, return-value detail is unnecessary; the description instead covers the things structured data cannot express — account prerequisite, credit behavior, and the not-unlocked fallback with the required confirmation step. Nothing an agent needs to call this correctly is missing.

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 coverage is 100% and the single plate parameter is fully documented there (UK plate, any spacing or case), so the schema does the heavy lifting. The description only ties plate to unlock state as a precondition, adding little beyond the schema; baseline 3 is appropriate.

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 — the detailed report of a car the user has unlocked on RegTail — and enumerates its contents (verdict, MOT tests, mileage, checklist, gaps). This is clearly distinguishable from free_check, sample_report, and unlock_report among the siblings.

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?

"Use to discuss a car in depth" gives the positive condition, and the fallback rule ("for a plate that is not unlocked it returns unlocked=false and a message; then ask the user before calling unlock_report") names the alternative tool and the exact condition that selects it.

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