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

Annotations already declare non-read-only, destructive, idempotent. The description adds a concrete auth requirement ("Requires custom_fields:write scope") and the server-side dispatch behavior for the legacy `value` shim, which are genuine additions beyond the structured hints.

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?

Three tight sentences with the primary action front-loaded, followed by invocation mechanics and the scope requirement. No filler, though the typed-column enumeration slightly duplicates the schema.

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?

An 8-parameter mutation tool with full schema coverage and annotations carrying the safety profile. The description covers the action, the invocation choice, and the required scope; with no output schema there is little else an agent needs before calling it.

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 schema already documents every parameter including the typed columns and the legacy `value` shim. The description restates the typed-column/`value` dispatch rather than adding syntax or constraints beyond it, so baseline 3 applies.

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+resource ("Update an existing custom field value by ID") that unambiguously distinguishes it from the create/delete/get/list siblings of the same resource. It does not name a sibling explicitly, but the mutation scope is clear.

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?

The description explains HOW to invoke (set the typed column matching field_type, or pass a single `value`), which is useful, but gives no explicit when-to-use/when-not-to-use guidance relative to create_custom_field_value, delete_custom_field_value, or list_custom_field_values. Usage is implied rather than stated.

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