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

Annotations already declare idempotentHint=true, destructiveHint=false, readOnlyHint=false, so safety is covered. The description adds real context beyond that: repeat calls are a no-op that preserves existing values, the result echoes the current languages, and modifications must happen outside this tool. It stops short of describing error behavior or the birth-date requirement's consequences.

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?

The purpose is front-loaded, but the second and third clauses are padded ('which Koboshi asks every new account, as its website does') and the field enumeration duplicates the schema. Content is useful but not tight.

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 mutation tool with full annotation coverage, no output schema, and fully documented parameters, the description covers preconditions, idempotent repeat behavior, and where the result lands. Only edge cases (validation errors, missing birth data) are unaddressed, which is a minor gap.

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%, so the schema already documents every parameter and the enum values. The description restates most fields (meanings language, learning language, secondary languages, birth month/year) but omits learning_level and adds no format or constraint detail beyond the schema. Baseline 3 is appropriate.

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 names a specific verb and resource (first-time setup writing the account's languages) and enumerates the fields involved, so an agent knows exactly what is being set. It does not name the sibling get_languages to distinguish read vs write, but the purpose itself is clear.

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?

It states the precondition explicitly ('first-time setup for a Koboshi account that has no languages yet' / 'still waiting to be set up') and the when-not ('an account whose languages are already chosen keeps them'), then routes existing-language changes to the app's Settings rather than this tool. This is unusually complete routing guidance.

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