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

Annotations already declare readOnlyHint=true and destructiveHint=false; the description reinforces this with 'Does not create anything' and adds genuinely new behavioral context: it returns multiple candidate couriers with codes and names, and it is a POST endpoint (unusual given the read-only nature). No contradiction with annotations.

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 purpose, then the workflow link, then the read-only assurance. 'POST /couriers/detect' is arguably implementation detail for an agent, but it is compact and non-redundant overall.

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 one simple parameter, no output schema, and annotations covering the safety profile, the description supplies everything needed: what it infers, what it returns, what to do with the result, and that nothing is mutated. No material gap remains.

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 100% and the single tracking_number parameter is fully documented in the schema. The description adds no format, length, or carrier-specific syntax guidance, so the baseline of 3 applies.

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 ('Find which couriers a tracking number most likely belongs to') and explicitly describes the return payload (matching courier codes and names). This is clearly distinguishable from siblings like list_couriers or get_tracking, which operate on known couriers rather than inferring them from a number.

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 names the downstream consumer explicitly: 'Use the code with trackingmore_create_tracking,' which tells the agent this is a lookup step preceding tracking creation. It does not state when not to use it (e.g., when the courier is already known and list_couriers would suffice), so it falls short of full alternative routing.

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