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

Goes well past the annotations (destructiveHint=true, idempotentHint=false) by naming the actual destructive behaviors: 'audiences' and 'tags' wholesale replace existing values, and 'unsubscribed: true stops all marketing email to it'. It also discloses side effects the agent cannot see elsewhere — that 'contact updated', 'tag added' and 'score changed' automations fire.

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?

Front-loaded with the purpose, then a single dense clause per parameter group — no filler. The quoted automation names add length but each carries behavioral information, so nothing is genuinely wasteful.

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 destructive, non-idempotent 11-param mutation with no output schema, the description covers the risky semantics (replacement, unsubscribe, automation triggers) that an agent most needs. It does not state that omitted fields are left unchanged, which is the main remaining gap for a partial-update tool.

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?

With only 45% schema coverage across 11 params, the description carries real weight: it explains the replace-vs-increment distinction for tags/audiences/add_tags/remove_tags and the effect of unsubscribed. It leaves email, first_name, last_name and custom_fields unaddressed, though those are largely self-describing.

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+resource ('Update a contact') and then enumerates which fields mean what, which lets an agent separate tag replacement from the add-contact-tags/remove-contact-tags siblings. It does not mention update-contact-score, which overlaps on the 'score' field, so the sibling differentiation is incomplete.

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?

Gives real selection guidance: 'tags replaces its tags (add_tags / remove_tags change them)' tells the agent when to use this tool versus the dedicated tag tools. It stops short of explicit exclusions, e.g. that a score-only change could go through update-contact-score instead.

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