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

No annotations are provided, so the description carries the full burden. It discloses the result limit ('Returns up to 5 matching payments') and that it returns 'full details'. However, it does not explicitly state that the operation is read-only (though 'look up' implies it), nor does it describe error cases, empty results, or rate limits. This is moderate transparency, but not exceptional.

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 consists of two concise sentences. The first sentence states the purpose with a clear verb and resource, and the second adds the key behavioral detail (result limit). There is no redundancy, fluff, or repetition of schema information. It is perfectly sized and front-loaded.

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?

The description provides the essential information: the tool's purpose, accepted identifier types, and return limit. Since an output schema exists, the return structure is already defined. The input schema covers parameter details. The only gap is lack of explicit guidance on choosing between this and similar tools (e.g., search_payments), but given the well-specified schema and description, it is largely complete for a simple lookup tool.

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 input schema covers both parameters with descriptions (100% coverage), so the baseline is 3. The tool description restates the query types but adds no new parameter-specific meaning beyond what the schema already provides. The description does mention the return limit, but that's about output, not parameters. Thus, it meets but does not exceed the baseline.

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 function: 'Look up payments by transaction hash, email, reference ID, customer ID, or invoice ID.' It uses a specific verb ('look up') and resource ('payments') and enumerates the query types. However, it does not explicitly differentiate itself from sibling tools like search_payments, so it doesn't fully earn a 5.

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 on when to use this tool: whenever you have one of the listed identifiers (transaction hash, email, reference ID, customer ID, or invoice ID). It implies the tool is for targeted lookups, but it does not explicitly mention alternatives or when not to use it, such as for broader searches that might require search_payments. This aligns with 'clear context, no exclusions'.

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