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

Annotations already declare readOnlyHint and openWorldHint, yet the description adds real value beyond them: self-billing counts as 1 metadata call, the endpoint is free, and the auth requirement (connected account or dv_sk_ key). That is meaningful operational context an agent cannot get from the annotations.

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 tight sentences that front-load the returned data, then billing, then endpoint and auth constraints. The parenthetical endpoint/auth block is slightly compressed, but every element earns its place.

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 parameters and no output schema, the description is the sole source of return-value detail, and it enumerates what comes back plus cost and auth requirements. Complete enough for a zero-arg read tool, though it could note the shape of the usage buckets.

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?

The tool takes zero parameters, so the schema carries nothing to interpret and the baseline is 4. The description correctly omits parameter discussion rather than padding it.

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 (Returns) plus the exact resources returned: the calling key, its scopes, environment, and today's usage across all 3 buckets. Clear and concrete, though it never differentiates itself from the closely related sibling keys_me.

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 a useful prerequisite (needs a connected account or a dv_sk_ key) and notes the call is free, which implies when it can be invoked. It does not state when to prefer this over siblings like keys_me or credits_checkout, leaving usage largely implied.

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