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

Annotations already declare the write/destructive/idempotent profile, so the description's real contribution is the cost model: unlocking draws down an account allowance and is free for already-unlocked prompts. It omits what happens when the allowance is exhausted or what the call returns, which would round out the picture.

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, zero filler, with the action and its billing consequence front-loaded ahead of the usage restriction. Nothing can be removed without losing information.

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 two-parameter mutation with no output schema, the description covers cost and usage gating but is silent on failure modes (insufficient allowance) and on the undocumented 'lang' parameter. Annotations handle the safety profile, so the gap is moderate rather than disqualifying.

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% for both parameters, so the description carries the full burden and doesn't meet it. Neither 'id' nor 'lang' (an enum with a default) is mentioned, leaving the agent to infer that 'id' means a prompt id and what 'lang' affects.

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 ('unlock one prompt') plus the billing mechanism ('using the account allowance'), which lets an agent distinguish this from the read-only siblings get_prompt and list_unlocked_prompts. It stops short of naming get_prompt as the non-mutating alternative.

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 only when the user requests access' is an explicit when-to-use gate with an implicit exclusion for proactive use. 'Already unlocked prompts cost zero' adds a second condition (this is not a re-read path), though no sibling is named as the alternative for that case.

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