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

Annotations cover the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=false), and the description adds genuinely useful behavior beyond them: the 10,000-row per-call batch limit and the fact that duplicates within the list are skipped. It still omits what happens on failure or partial success, but that is a modest gap against the annotation coverage.

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 short sentences, zero filler, with the core action and its most important constraint (the batch cap) front-loaded. Every clause earns its place.

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 non-destructive mutation with annotations and no output schema, the description covers the action, the size limit, and dedup behavior. However, with 33% schema coverage and an undocumented nested contacts object, an agent still lacks enough detail to construct valid payloads confidently.

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 only 33% and only organization_id carries a description. The description states the 10,000 cap, which merely restates the schema's maxItems, and says nothing about the contacts item shape (which is an undocumented bare object) or the contact_list_id semantics. It does not compensate for the coverage gap.

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 ('Append rows to an existing contact list'), and the word 'existing' distinguishes it from the sibling create_contact_list. An agent can tell at a glance that this adds to a list rather than creating one.

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 phrase 'existing contact list' implies the list must already exist, which is useful context, but there is no explicit when-to-use guidance, no conditions or prerequisites, and no routing to siblings such as create_contact_list or list_contacts. Usage is only implied.

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