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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so safety is covered structurally. The description adds genuine value by enumerating what the response contains and framing the call as a pre-flight discovery step. Minor gap: no note on size/volume of the returned field list for large sites.

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 sentences, front-loaded with the return contract before the call-to-action guidance. No filler; the uppercase 'AND' efficiently flags that two distinct vocabularies come back.

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 two-parameter read-only tool with no output schema, the description compensates by describing the returned fields and pipeline stage keys explicitly, plus the downstream workflow it feeds. Nothing an agent needs to invoke it correctly is missing.

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% for both `site_id` and `user_goal`, so the schema already carries the semantics. The description adds nothing about either parameter (e.g. that `site_id` scopes the vocabulary returned), 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 and resource plus the exact payload: custom attribute keys, labels, types, select options, and the pipeline stage keys `status` accepts. This distinguishes it from `define_contact_field` (which creates) and `list_contact_filter_vocabulary` (which lists filter terms, not field definitions).

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 says 'Call this BEFORE upsert_contacts when importing' and gives the reason (map a spreadsheet onto the site's existing vocabulary rather than inventing duplicate keys). The alternative tool and the condition selecting this one are both named.

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