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

Annotations already provide readOnlyHint=false, idempotentHint=true, and destructiveHint=false; the description adds context on top: omitted month cap means unchanged, 0 removes the cap, return JSON differs depending on whether budget or services changed, and authentication is required ('Needs your API key'). Minor gaps remain—behavior when both budget and services change is ambiguous—but the description carries substantial behavioral weight beyond 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?

The description is dense and logically ordered: what it does, what fields mean, when to use it, what it is not, and what it returns. Every sentence carries information, though a little redundancy with the schema's window values and the trailing auth note could be tightened.

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 is responsible for explaining the return shape, and it does so conditionally for budget vs services changes. It also covers auth, parameter semantics, and exclusions. It doesn't detail error behavior or simultaneous-field-change returns, but for a 5-param config tool with 100% schema coverage and annotations, it is nearly complete.

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 coverage is 100%, so the baseline is 3. The description adds meaningful semantics: it explains the omitted/0 behavior of monthly_request_cap, enumerates the actual service keys accepted by enabled, and examples for caps and window behavior. That is more than the schema alone provides.

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 leads with a specific verb and resource ('Configure one API key of your account by id'), names exactly what can be changed (monthly_request_cap, enabled, caps), and explicitly distinguishes itself from configure_services and revoke_api_key. An agent can tell this tool apart from its siblings without reading the 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?

It states when to use the tool ('Use it to budget or restrict one key'), where ids come from ('key ids come from list_api_keys'), and explicitly says when NOT to use it ('Not for account-wide service settings (use configure_services) and not for revoking (use revoke_api_key)'). This is exactly the guidance needed for correct selection.

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