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

Goes well beyond the annotations (destructiveHint=true, idempotentHint=true): it discloses that firstName/lastName overwrite existing values, that missing tags are created as a side effect, and that suppression/bounce-listed emails are counted but not added. It also describes the return payload (inserted, alreadyExisting, addedToList) in the absence of an 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?

Three sentences, front-loaded with the core upsert semantics, then the sibling routing, then the return/edge-case detail. Every clause carries information an agent cannot get from the structured fields.

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?

Covers create-vs-update logic, tag side effects, suppression-list edge cases, and the return shape for a 5-parameter mutation tool with no output schema. Minor omissions remain: whether matching is scoped per-list or globally, and how this tool differs from directiq_add_contact_to_list.

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 the schema itself documents every parameter, including the overwrite behavior and the directiq_list_lists provenance of listId. The description's only additional hint is that tags are created when missing, which the tags schema description already states, so baseline 3 is correct.

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 precise verb pair and resource (create-or-update a contact in a list) and spells out the branching logic: new email creates, existing email updates names. It explicitly names directiq_update_contact as the tool for other field changes, so an agent can separate the two without opening either schema.

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?

"Use this to create contacts; to change other fields on an existing contact, use directiq_update_contact" gives an explicit when-to-use plus a named alternative. The gap is that the near-identical sibling directiq_add_contact_to_list is never mentioned, leaving the create-and-attach vs add-existing distinction to inference.

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