api_budget

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

Goes well beyond the readOnlyHint/openWorldHint annotations by disclosing accounting semantics that directly affect how the returned numbers must be read: per-month key caps, ledger persistence across restarts, and the rule that cached repeats cost nothing and are not counted. These are exactly the behaviors an agent needs to interpret spend correctly.

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 spend figure is front-loaded in the first sentence and the following sentences each carry useful accounting context. 'Beside the cache' is minor implementation detail, but nothing is padded or redundant.

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, read-only reporting tool with no output schema, the description covers what is measured and the counting rules. It stops short of naming the return shape or units/currency, which would fully close the loop, but the essentials are present.

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 baseline of 4 applies. The description adds nothing parameter-related because there is nothing to add.

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 with scope: 'Report the key's Catalog API spend, this session and this month.' This is unmistakably distinct from the eighteen sibling search/get tools, which all retrieve records rather than account-level usage.

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?

Usage is implied rather than stated: the note about the monthly cap and long sweeps hint at when an agent should care, but there is no explicit 'call this before/after X' instruction. No alternatives are named, though none exist among siblings, so the guidance gap is mild.

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