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

Annotations only supply destructiveHint=true; the description adds real context beyond that — 'existing contacts are not removed' scopes the destructive risk, 'WRITE' flags mutation, and the dynamic-list prerequisite is a behavioral requirement not visible in the schema. It stops short of describing auth needs or return behavior.

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?

Four tight clauses, front-loaded with the WRITE marker and the operation, then prerequisites, then side-effect clarification. Nothing is redundant and the endpoint reference is compact.

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 no output schema, the description carries return-value burden, but for a PUT mutation that's minor. It covers side effects, limits, prerequisites, and endpoint; only the response shape and permission requirements are left unstated.

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% and each parameter is fully documented in the schema, so the baseline is 3. The description's '500 contacts' cap and dynamic_data prerequisite largely restate what maxItems and the nested schema already convey.

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 ('renames a contact list and/or adds up to 500 contacts to it') and immediately disambiguates from siblings like create_contact_list, list_contact_lists, and send_sms. An agent can tell what the tool does without opening the schema.

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 clear context: 'Adding dynamic data needs a list created as dynamic' is a prerequisite, and 'It does not send anything' rules out the send_sms sibling. However, it never explicitly contrasts with create_contact_list or get_contact_list, so exclusions are implied rather than stated.

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