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

The readOnlyHint annotation already declares this a safe read. The description adds useful behavioral context beyond that: the endpoint mapping (GET /transactions/{id}) and the fact that related resources can be embedded via zoom. It does not describe error behavior for missing/nonexistent ids, but with annotations covering safety this is adequate.

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 compact sentences with the core purpose front-loaded and the endpoint mapping trailing as a secondary detail. No filler.

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 simple two-parameter read tool with no output schema, the description covers purpose, retrieval key, and the zoom option, matching the schema's documentation. Only the absence of error/not-found behavior keeps it short of full completeness.

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 both parameters are already documented in the schema. The description's mention of zoom examples (items, customer, payments, applied_taxes) broadly repeats the schema's example rather than adding new syntax or constraints. Baseline 3 applies when the schema carries the parameter burden.

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 and resource with scope: 'Get a single transaction by id'. The word 'single' implicitly distinguishes it from the sibling foxy_list_transactions, and the zoom capability is named. An agent can identify this as the by-id retrieval tool without opening the schema.

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 implied by 'by id' versus the list sibling, but the description never explicitly states when to prefer this over foxy_list_transactions or what happens if the id doesn't exist. Context is present but no explicit when/when-not guidance is given.

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