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

With annotations carrying only destructiveHint=true, the description does the heavy lifting: it discloses that tags/phones/emails replace rather than append (and that existing entries must be resent), that contacted=true pauses action plans, and that source/sourceUrl are immutable after creation. These are exactly the destructive side-effects an agent must know before mutating, well beyond what the annotations convey.

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?

The text is dense and front-loaded, leading with the replacement caution that carries the most risk and then layering immutable-field and workflow notes. Every clause earns its place with no filler or repetition of the tool title.

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 19-param destructive mutation with no output schema, the description covers the dangerous semantics, points to fub_list_stages and fub_list_custom_fields for valid values, and identifies immutable fields. It omits guidance on multiple unlisted parameters (price, addresses, assigned*), so it is strong but not fully complete.

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 low (32%) across 19 parameters, so the description must compensate; it adds real meaning for the highest-risk params (tags, mergeTags, phones, emails, contacted) and even documents source/sourceUrl, which are absent from the schema. However, most parameters (price, stage, addresses, assignedTo, background, customFields, assigned*) receive no added explanation, leaving the compensation partial.

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 states a specific verb and resource – 'Update a contact's fields' – which is unambiguous against CRUD siblings like fub_get_person or fub_create_deal, and it names the underlying PUT /v1/people/{id} endpoint. It never explicitly contrasts itself with fub_update_deal or fub_update_task, so it falls short of the top band.

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 conditional behaviors (mergeTags, contacted) but never states when to reach for this tool versus fub_get_person, fub_update_deal or the other update siblings. Usage is implied by the name rather than guided, so this sits at the minimum-viable level.

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