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

With no annotations, the description carries the burden and does disclose meaningful behavior: currency defaults to GBP, the key must be a GUID from list_plans, and an unknown key returns an error. It never states the operation is read-only or mentions auth/rate-limit constraints, so it is not fully complete, but the error and default semantics are genuinely useful.

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 compact sentences, each earning its place: purpose and payload first, key format second, currency and error behavior last. No filler or repetition.

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?

No output schema exists, and the description names what is returned (per-cycle prices, config options, add-ons), so an agent knows the payload shape. Combined with the key format and currency default, everything needed to call it correctly is present.

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 0%, so the description must compensate and does: 'key' is defined as the plan's GUID from list_plans (not the name), and 'currency' is an optional ISO code restricted to GBP/EUR/USD/AUD defaulting to GBP. Both parameters are fully disambiguated.

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 ('Get one UmbHost hosting or licence plan by its key') and enumerates what comes back: per-cycle prices, config options, add-ons. The phrase 'one ... plan by its key' cleanly separates it from the sibling list_plans.

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 routes the caller to list_plans for the key and warns that the name will not work, plus notes an unknown key errors. It lacks an explicit 'do not use when...' clause, but the retrieval context is unambiguous.

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