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

Annotations already carry readOnlyHint/idempotent/destructive=false, so the safety profile is covered; the description still adds the meaningful claim that it never returns the key and clarifies the null-means-no-limit semantics of the spending limit. It does not describe the response shape beyond field names, but with the safety profile already structured that is a minor gap.

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 tight sentences: contents first, then the workflow trigger, then the safety guarantee. Every clause carries information and nothing is repeated verbatim from annotations beyond a two-word 'Read-only'.

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 zero-parameter, no-output-schema tool, the description enumerates the returnable fields and states the key is never returned, which is everything an agent needs to call and interpret it. No missing prerequisites or auth caveats.

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 no parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The 'null means none' note concerns a returned field rather than an input, and is useful but not a parameter-semantics contribution.

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?

Names a specific verb and resource (read the connected key's account) and enumerates exactly what comes back: available and reserved credits, scopes, the per-call spending limit, and where credits are added. No sibling in the list (daystruct_status, discover_daystruct_capabilities) covers this same surface, so an agent can pick it without opening a 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?

Explicitly prescribes when to call it: before a paid call, show the user the price first, and report spend afterwards. That is a concrete when-to-use workflow rather than implied context.

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