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

Annotations already declare this is a non-read-only, non-idempotent, destructive write, so the safety profile is covered. The description adds genuinely useful behavioral detail beyond that: a per-row import report is returned and invalid rows are reported rather than failing the whole list, which tells the agent the operation has partial-success semantics.

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 tight sentences, front-loaded with the action and resource, then the return/failure behavior. No filler or repetition of the title.

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?

Return behavior is covered despite no output schema, and annotations cover the mutation profile. However, the description omits permission/workspace requirements, behavior on name collision (whether an existing list is overwritten, which matters given destructiveHint=true), and the 10,000-row cap that only exists in the schema.

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 20%, and the description compensates only for the contact-row fields (phone_e164, name, first_name, language, time_zone, external_reference, variables). The required top-level parameters project_id and name, plus source and organization_id, receive no explanation in the description, so the burden is not met.

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?

State a specific verb and resource ('Create a contact list in the workspace') and clarifies that rows are optional. It does not explicitly differentiate itself from the close sibling add_contacts, which also adds contacts, so an agent still has to infer the boundary.

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?

No when-to-use guidance, no prerequisites, and no named alternative such as add_contacts for appending to an existing list. The only hint at usage is 'optionally with rows', which is a capability statement rather than routing guidance.

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