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

The annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered structurally. The description adds nothing beyond that: no mention of filtering behavior, pagination, whether all definitions or a paginated page is returned, or any auth/scope requirements. A duplicate of the endpoint path is not behavioral information.

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?

It is short, but the first sentence is repeated verbatim, which is pure waste. The only marginally useful content, the operation ID and the describe_operation pointer, would stand fine on its own.

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?

With no output schema, 0% parameter documentation, a nested params object, and no annotations beyond the flags, the description leaves everything an agent needs unresolved. It doesn't say what the response contains, how results are scoped, or what to pass in query.

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% for two parameters (query and params, the latter a nested empty object), so the description must compensate and it does not. Neither parameter is mentioned or explained; the agent gets no idea what to put in query.

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, GET /api/contacts/custom-fields/definitions, which is already implied by the tool name and title. It never says in plain language what the tool returns (custom field definitions for contacts) or how it differs from siblings such as get_global_settings_custom_field_definitions or get_contracts_by_id_custom_fields_defin. This is close to tautology.

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 statement of when to use this versus alternatives, no prerequisites, and no exclusions. The only actionable hint is the pointer to describe_operation for native request schemas, which is a schema-discovery instruction rather than usage guidance.

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