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

Annotations provide only destructiveHint=true, so the description carries most of the burden and does add real context: the 500-contact cap, the uniqueness requirement on name, and the side-effect clarification that nothing is sent. It stops short of stating what happens on a duplicate name (error vs overwrite) or whether the call is idempotent.

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?

Three short sentences, front-loaded with the operation class and key constraints, with no filler. The REST endpoint clause is useful for API-literate agents but is the least essential sentence.

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 4-parameter write tool with full schema coverage, no output schema, and minimal annotations, the description covers operation class, key constraints, and the no-send side effect. The main remaining gap is error/duplicate-name behavior, which is minor here.

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%, so the schema already documents name, country, contacts, and description fully. The description's extra details (500 contacts, unique name ≤32 chars) largely restate schema constraints, so baseline 3 applies.

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 ('creates a new contact list') and labels the operation class ('WRITE'), which cleanly separates it from the sibling 'update_contact_list', 'get_contact_list', and 'list_contact_lists'. The POST /contacts endpoint mapping further pins down the operation.

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 WRITE label tells the agent this is the creation path, and 'It does not send anything' implicitly redirects messaging intent to send_sms. No explicit when-to-use/when-not conditions or named alternatives (e.g. update_contact_list for existing lists) are given.

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