Get a customer's full picture

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

Annotations already mark the tool as read-only. The description adds behavioral context: it returns specific fields (monthly cents, entitlement count, read-cost) and explains the no-match handling. This goes beyond the annotations but does not cover permissions or rate limits.

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 concise (about 120 words) and structured logically: first sentence for purpose, second for outputs, third for parameter usage, fourth for use case, fifth for edge case. No wasted words, front-loaded with key information.

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?

Despite no output schema, the description clearly states what is returned (monthly cents, entitlement count, read-cost). It also covers the no-match case. With 7 optional parameters, the description explains how to use them (any one). This makes the tool's behavior fully comprehensible for an AI agent.

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 schema has 7 parameters with individual descriptions, but the description adds crucial semantics: 'Identify the person by ANY ONE of the identifiers below; they all resolve to the same canonical customer.' This clarifies mutual exclusivity and selection logic, which is valuable beyond the schema's per-parameter descriptions.

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 clearly states the tool's purpose: to cross-match a customer across identity layers and return billing and cost data. It specifies the resource (customer) and the verb (cross-match/get), and distinguishes from siblings like get_revenue by offering a combined view.

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 explicitly says 'Use for how much does this user pay and what do they cost us?' which gives a clear use case. It also mentions that a no-match returns an informational result rather than an error. However, it does not explicitly mention when not to use this tool or reference sibling tools as alternatives.

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