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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false, and destructiveHint=false, so safety is covered. The description adds genuine value by revealing scope (account-wide, not per-contact) and that dropdown fields include their choice options. It does not say whether all fields are returned or whether there is pagination, though with zero parameters and a closed-world read, that gap is modest.

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?

A single short clause with no padding, and the key qualifier ('for dropdown fields') is included rather than omitted. Its only weakness is being a sentence fragment, which makes the intent slightly less crisp than an explicit 'Returns ...' phrasing.

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-parameter, non-destructive read tool with annotations covering the safety profile and no output schema, the description supplies what matters: what entity the fields belong to and that dropdown choices are included. Return-value structure (field types, ordering) is unspecified, but that is a minor omission at this complexity.

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?

There are no input parameters, so the baseline is 4. The description correctly implies the tool takes no filtering input and returns everything for the account, matching the empty schema.

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 names the resource precisely: the account's custom contact fields, plus the choice values for dropdown-type fields. That distinguishes it from generic list_* siblings like list_tags or list_lists by content. It lacks an explicit verb (no 'list'/'retrieve'), so it reads as a noun phrase rather than an action statement.

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 guidance on when to call this versus alternatives, nor any prerequisites or follow-up workflow (e.g., using the returned field IDs with update_contact). The agent must infer usage entirely from the tool name.

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