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

Goes well beyond the annotations by warning that SlickText workflows (Contact Created / Contact Field Changed / Contact Added to List) can fire on this event and send REAL texts or take other configured actions. It also discloses the return value (membership count) and the underlying endpoint, which matters since there is no output schema.

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?

A single dense paragraph with the operation type and action front-loaded, followed by the consequence warning, return value, and endpoint. Every clause carries weight, though the parenthetical about opt-in and audiences could be tightened slightly.

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 two-parameter mutation tool with no output schema, the description covers all the gaps: what is mutated, what is NOT mutated, the side-effect risk of workflows, what is returned, and the REST path. Nothing an agent needs in order to invoke it safely is missing.

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 both parameters are documented in-schema (list_ids points at slicktext_list_lists, contact_id is a positive integer). The description's 'one contact to one or more lists' merely restates the schema cardinality, adding no new syntax or format detail, 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 ('add one contact to one or more contact lists') and immediately scopes it: it does not change opt-in status, and lists are campaign audiences. The 'WRITE:' prefix and the POST endpoint make it unmistakable against read siblings like slicktext_list_list_contacts or slicktext_create_contact.

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?

Clearly frames when this applies (attaching an existing contact to audience lists) and implicitly contrasts with opt-in changes, which belong to slicktext_update_contact. It does not name alternatives or state exclusions explicitly, so it stops short of full routing guidance.

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