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

The description adds useful behavior beyond the annotations: workspace and credential prerequisites plus a specific 403 refusal condition. It does not cover return behavior or duplicate handling beyond stating that external_id is unique within the customer, but annotations already declare the non-read-only, non-destructive, non-idempotent safety profile.

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?

The description is front-loaded with the core action and required parameters, then adds prerequisites without unnecessary prose. Both sentences carry useful information and avoid repetition.

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?

Given full schema parameter descriptions and annotations covering safety and idempotency, the description is complete enough to invoke the tool correctly. It could be stronger if it mentioned what the tool returns or how duplicate external_id conflicts are surfaced, since no output schema exists.

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 all seven parameters. The description lists required and optional fields and repeats that external_id is unique within the customer, but adds little semantic detail beyond the schema.

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 states a specific action and resource: "Add a contact to a customer." It also names the customer relationship and required fields, which clearly distinguishes creation from sibling operations such as update_contact or delete_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?

It gives important usage context: a claimed Last Price credential and claimed workspace are required, and sandbox self-registration keys are refused with 403 until claimed. It does not explicitly route the agent to alternatives such as update_contact for existing contacts, so it stops short of full 5-level guidance.

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