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

The readOnlyHint annotation already establishes this as a safe read, so the bar is lowered; the description adds the backing endpoint (GET /v2/fielddefinitions) and clarifies the semantic scope of what is listed. It adds no auth requirements, rate limits, or pagination behavior beyond what the schema's limit/offset already convey.

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 tight sentences with the purpose front-loaded and a clarifying parenthetical; nothing is padded. The API-endpoint sentence is mildly redundant with the tool name but earns some place as a mapping hint, so it falls just short of 5.

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 zero-required-param, read-only list tool with full schema coverage, the description is essentially sufficient, and the parenthetical partially compensates for the absent output schema by hinting at what is returned. It could go one step further and describe the returned definition shape or paging expectations.

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 typed limit/offset params and the catch-all params object are already documented in the schema. The description references none of them and adds no syntax or filtering detail, making the baseline 3 correct.

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 (List) and resource (custom-field definitions) and even resolves the ambiguity of that resource with a parenthetical defining it as the schema for custom fields on properties/bookings/guests. It is clearly distinct from siblings like list_properties or list_bookings, but it never explicitly contrasts itself with an alternative, which a 5 would require.

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?

There is no when-to-use guidance, no prerequisites, and no named alternative. The description only says what the endpoint is; an agent gets no help deciding when this tool is the right call versus fetching the entities themselves.

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