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

The description goes well beyond the annotations: it reveals the tool performs pattern detection only and does not fetch live parcel status, and it also explains the pricing model, the prepaid header option, the free daily call, and the lack of wallet/API key requirements. This is highly valuable behavioral context that annotations do not provide.

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?

Each sentence earns its place: purpose, scope exclusion, required input, pricing, and auth are all stated in a compact, logical order. The description front-loads the core question and behavior before cost details, making it easy for an agent to quickly grasp what the tool does.

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?

For a single-parameter tool with a full input schema and an output schema present, the description provides all necessary context: what it returns, what it does not do, required input, and cost/auth constraints. Nothing essential is missing for an agent to decide whether to call this tool.

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 input schema already has 100% coverage for the single required parameter 'tracking' with description 'Tracking number'. The description only repeats 'Required input: tracking' and adds the general idea that the tracking-number shape is used, but does not add concrete details like format examples, expected length, or carrier-specific patterns.

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 opens with a specific question and names the exact verbs and resource: it guesses carriers (UPS/FedEx/USPS/DHL/DPD/TNT/TR) from tracking-number shape and returns a carrier tracking URL. This is precise and distinguishes the tool from all siblings, none of which deal with tracking-number carrier detection.

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?

The description clearly frames the use case as 'Which carrier is this tracking number?' and gives an explicit when-not: 'Live parcel status is NOT fetched — pattern detection only.' It could strengthen this by naming an alternative tool for live tracking, but no such sibling exists, so the guidance is clear and adequate.

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