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

Annotations already declare destructive=true, readOnly=false and idempotentHint=false, so the safety profile is covered. The description adds a genuinely new behavioral trait not present in structured fields: duplicates already in the list are silently skipped, which materially affects the outcome of a call. It does not describe partial-failure behavior or permission requirements.

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, front-loaded with the core action and immediately followed by the two constraints. The cap restates maxItems=10000 already in the schema, a minor redundancy, but nothing is padded or buried.

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 bulk-write tool with no output schema and low parameter coverage, the description covers the batching limit and dedup semantics but omits the shape of each contact object, whether the operation is atomic or partial, and any authorization requirements. Adequate as a minimum, but an agent could still mis-invoke it by sending wrong item structures.

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%: contact_list_id and especially the contacts array carry no description, and the array's item type is an untyped object. The description does not compensate — it never explains what fields a contact row must contain, nor clarifies the required list identifier, leaving the most important input structure undocumented.

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 names a specific verb (append) and resource (rows in an existing contact list), which unambiguously separates it from siblings like create_contact_list and list_contacts. The word 'existing' signals it operates on an already-created 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?

Usage is only implied: the agent can infer this is the tool for adding contacts to an existing list, and the 10,000 cap implies batching constraints. There is no explicit when-to-use statement, no prerequisites (e.g., required scopes or list-must-exist), and no pointer to alternatives such as create_contact_list.

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