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

readOnlyHint=true already tells the agent this is a safe read, so the description only needs to add context. It contributes the REST route (GET /transaction/{transactionId}), which is mild value, but discloses nothing about the returned payload, missing-ID behavior, or auth scope.

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 short sentences, front-loaded with the purpose. The trailing REST endpoint restatement is mildly redundant with the purpose sentence but costs little.

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 single-parameter getter with a covering annotation this is nearly sufficient, but with no output schema the description should say something about what a transaction object contains or how errors surface. As written it leaves the return value entirely unspecified.

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?

Schema description coverage is 100%, so the single transactionId parameter is already documented in the schema. The description restates the ID requirement but adds no format, prefix, or example beyond what the schema provides, making the 3 baseline appropriate.

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+resource and scope ('Get a single payment transaction by ID'), which lets an agent distinguish it from the list-style sibling mercoa_find_transactions without opening either schema. It stops short of naming that sibling explicitly, so sibling differentiation is implied rather than stated.

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?

'by ID' implies the retrieval condition and contrasts implicitly with the find_* family, but there is no explicit when-to-use guidance, no exclusions, and no prerequisite or error-handling note for an unknown ID.

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