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

Annotations already declare readOnlyHint=true and openWorldHint=false, so a 3 is the right bar. The description nonetheless adds real context beyond them: prices are indicative EUR including VAT for one black-and-white page, rest-of-world destinations may be handled manually with longer delay, and each service level has defined proof semantics.

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 purpose, then usage, then the service-level glossary; every clause carries information. It is on the long side and repeats the ISO code example already present in the schema, costing a point.

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, no-output-schema read tool this is complete: it describes what is returned (country, service level, from-price, delivery time, legal product name), the currency and VAT basis, and the caveat about manual rest-of-world handling.

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 schema already documents the ISO 3166-1 alpha-2 format, the "DE" example and the omit-for-everything behaviour. The description largely restates that, adding only the intent of narrowing the answer, so baseline 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: lists destination countries and service levels Courio can mail a physical letter to, plus indicative price, delivery time and legal product name. This clearly distinguishes it from siblings quote_letter (pricing) and send_letter (dispatch) without needing to open 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?

Explicitly says to call it before quote_letter to check a destination is served, naming the alternative and the ordering. It also notes no account or API key is needed, removing a common precondition question.

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