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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered; the description adds meaningful behavior by documenting the returned field shape and the empty-list case ('none has been defined yet'). It does not cover ordering, pagination, or whether archived/hidden fields are included, which is the remaining gap.

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 zero filler: the return shape comes first, the slug cross-reference second, the creation path last. Nothing is redundant with the title or with structured fields.

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?

There is no output schema, so the description correctly carries the return-value burden by naming every attribute and the select-options case, and it disambiguates the empty result. For a single optional-parameter read tool this is sufficient to call correctly.

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?

Only one optional parameter (workspaceId) and the schema description already covers it at 100% coverage, including the fallback to a connection-bound or account workspace. The description adds no parameter-level meaning beyond the schema, so the baseline of 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 and resource ('List the custom fields defined for contacts') and immediately enumerates the returned attributes (name, slug, type, options), so the agent knows exactly what comes back. It is clearly distinct from create_custom_field (writes) and set_contact_field (sets values).

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?

Explicitly routes the agent: use this list to obtain a `slug`, feed that slug to set_contact_field, read values via get_contact, and use create_custom_field to add new fields. That is a concrete when-to-use-this vs when-to-use-siblings mapping rather than inference.

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