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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior, so the safety profile is covered structurally. The description contributes nothing beyond that: no mention of what is returned, whether values are keyed by definition ID, or how missing values behave. Pure duplication of the endpoint string adds no behavioral context.

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 single substantive sentence is duplicated verbatim, then followed by an operation-ID fragment and a pointer to another tool. There is no front-loaded statement of purpose, so the structure wastes its only available space.

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?

Placeholder: re-evaluating. The tool has 2 parameters, one of them an unconstrained open object, no output schema, and a description that explains neither the query object nor the response. Against that complexity the description is far from complete.

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 0%, so the description must compensate and does not. It implies the ':id' path parameter but says nothing about the free-form 'query' object (additionalProperties, no properties defined) — an agent has no idea what query keys are valid (e.g., definition IDs, pagination).

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 only restates the HTTP path in prose ('GET /api/contacts/:id/custom-fields/values') twice, which conveys the resource and verb only indirectly. It gives no natural-language statement like 'retrieve custom field values for a contact', and offers no differentiation from siblings such as get_contacts_by_id_dbf36acebdfb38a01cccfd33 or get_contacts_custom_fields_definitions.

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 mention of alternatives. The only directional hint is the boilerplate 'describe_operation provides native request schemas', which points at a different tool rather than explaining selection among the contact-related siblings.

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