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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, and the description adds what they cannot: it requires a signed-in connection, takes no arguments, changes nothing, and documents the exact return shape including edge cases (credits is 0 when empty, next_expiry is null when none).

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 return contract, then the buy path. Dense parentheticals make it long, and the buy_pack/buy_credits_at passage drifts toward documenting a sibling, but every clause carries actionable 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?

With no output schema, the description must supply the return contract, and it does so fully (account, credits, next_expiry shape, buy_credits_at). Auth requirement and side-effect profile are both covered, leaving nothing an agent needs before calling.

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?

Zero parameters, so per baseline this scores 4; there is nothing for the description to disambiguate. It usefully documents the return field semantics instead, though that is technically output rather than input semantics.

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+resource ('the signed-in customer's Odile Formats credit balance') and immediately situates it against siblings by naming unlock_job and buy_pack. An agent can tell this apart from the other get_* tools 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?

Gives explicit trigger conditions ('use it before unlock_job to check the job is affordable, or when the customer asks') and routes the alternative case ('to buy more: buy_pack') to the correct sibling, including the required billing:checkout permission.

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