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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety and repeatability are covered structurally. The description adds the shape of the returned record (slug, counts, cheapest cost, networks), but says nothing about ordering, exhaustiveness, or how fresh the 'cheapest average monthly cost' figure is. With annotations carrying the behavioral baseline, this is moderate added value.

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?

Two sentences, zero filler: the first front-loads what is returned, the second front-loads why an agent would call it. No restating of the name or title.

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 no output schema, the description correctly shouldered the burden of describing the return fields and did so. The only remaining gap is ordering/pagination behavior for the provider list, which is minor given a small, closed-world enumeration.

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?

There is a single optional parameter with 100% schema description coverage, including its enum and 'Default de' note, so the schema does the work. The description never mentions 'language' or what changes when it is set, leaving it at the baseline for high-coverage schemas.

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?

Specific verb+resource ('Lists the German mobile providers') plus an explicit inventory of the returned fields: slug, phone/data tariff counts, cheapest average monthly cost, and networks. It also states the downstream role of the output (the slug filters a tariff search), which lets an agent distinguish it from get_tariff and search_tariffs 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?

'Use it to see which providers are covered and to get the slug that filters a tariff search by provider' gives a clear trigger and an implicit route to search_tariffs. It stops short of an explicit exclusion (e.g. 'do not use this to fetch tariff details, use get_tariff'), so it is clear context rather than full when/when-not guidance.

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