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

Annotations already declare readOnly=false, idempotent=true, destructive=false; the description adds the important PATCH semantics and the destructive-ish 'tags replaces the tag set' warning plus the add_tag workaround. It doesn't mention permission requirements or what happens to suppressed contacts, but the safety profile is well covered.

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: the core action and field list come first, the side-effect caveat and alternative come second. Nothing is redundant with the title or 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?

With an output schema present and rich per-parameter descriptions, the description only needs to carry semantics and routing, and it does both. The one gap is that it doesn't clarify the boundary against upsert_contact for create-or-update flows.

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 coverage is 89%, so the baseline is 3; the description earns extra by restating the non-obvious destructive semantics of 'tags' and offering add_tag as the merge path. The remaining fields are already documented per-parameter in the schema, so no further gain was possible.

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?

Specific verb+resource ('Update fields on an existing contact') followed by an enumeration of the updatable fields (stage, lifecycle, email/phone/name, do_not_contact). The mention of add_tag as the merge alternative separates it from the tag sibling tools.

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 tag-adding to add_tag rather than this tool, and the 'only fields you pass are changed' clause tells the agent this is a partial update. It never contrasts with upsert_contact, which is the most likely sibling to confuse this with.

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