Spending rules

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered; the description adds that the rules are user-mutable only, meaning there is no write path here and the agent should not look for one. It also discloses the field-level shape of the returned configuration, which annotations cannot express.

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 sentences, front-loaded with the resource definition, followed by the read-only constraint. The middle enumeration is dense but each item earns its place by telling the agent what data is available without an output schema.

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 carries the burden of describing the return shape, and it does so by listing the rule categories an agent can expect. What is missing is only a hint about when to consult it versus spending_status.

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 baseline is 4; there is nothing for the description to disambiguate. It correctly spends no words on arguments.

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 gives a specific noun-resource ('the rules the guard enforces') and then enumerates exactly what those rules cover: payable networks, daily/per-payment limits, approval threshold, price-spike ratio, and allowed services/addresses. An agent can tell this is a configuration/policy read rather than a live status or a payment action, though it never names the siblings it differs from.

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 only implied: the content list hints the agent should read this before deciding whether a payment is permissible, but there is no explicit 'use this when...' clause and no discussion of spending_status or pay_and_fetch as alternatives. 'Read only: only the user can change them' is a constraint, not routing guidance.

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