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

Annotations already declare destructiveHint=true, idempotentHint=true, and readOnlyHint=false, so the mutation profile is covered. The description usefully adds the auth scope requirement, but it does not explain what makes this destructive (e.g., changing field_type or dropping field_options may invalidate existing stored values), which is the behavior an agent most needs here.

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 action and identifier front-loaded and the auth prerequisite second. No filler, nothing to trim.

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 annotations covering the safety profile and the schema documenting every parameter, the description supplies what is needed to call the tool: the action, the required ID, and the scope. Only the semantic consequences of editing an existing field definition (type changes, option removal) are missing, which is a minor relative gap given full schema coverage.

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% across all 8 properties, including the enum on field_type, so the schema carries parameter meaning fully. The description adds no syntax, format, or partial-update semantics beyond it, making the baseline 3 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 and resource ('Update an existing custom field definition by ID'), which clearly separates it from update_custom_field_value and the many other update_* siblings by name. However, it never explicitly contrasts with those alternatives, so it stops short of a 5.

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?

Provides one actionable prerequisite ('Requires custom_fields:write scope'), which is genuine usage guidance. But it never says when to use this versus create_custom_field_definition, delete_custom_field_definition, or bulk_update, leaving the when-to-use decision implied by the name alone.

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