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

Annotations only declare readOnlyHint=true; the description adds valuable behavioral context: only configured limits appear, the optional user_aggregate object covers account-wide caps, and those caps can deny a purchase even when per-agent rules are not exceeded. This goes well beyond the annotation and clarifies how the read-only result should be interpreted.

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 sentences, with the main purpose front-loaded and each subsequent sentence adding meaningful detail about response behavior. No filler or repetition of annotation/structured data.

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 carries the responsibility of explaining the response. It names the relevant fields, distinguishes per-agent from account-wide limits, and notes the conditional presence of limits. This is sufficient for an agent to correctly invoke and interpret the result.

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 has zero parameters, so there is no parameter semantics burden for the description to carry. The description instead explains the meaning of the response fields and the optional user_aggregate object, which is appropriate given the empty schema.

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 uses a specific verb and resource ('Get current spending vs. configured limits') and lists the exact fields returned. It is clearly distinct from siblings like request_purchase (a mutation) and retrieve_card (card data), so an agent can tell what this tool is for without opening schemas.

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?

The description provides clear context about what the tool returns and explains the per-agent versus cross-agent distinction, making its purpose obvious. It does not explicitly state when not to use it or name alternatives, but with only zero parameters and clearly distinct siblings, the implied usage is strong.

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