mercury_create_customer

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

Discloses side effects (writes new customer, persistent, not idempotent). Annotations only show destructiveHint: false and openWorldHint: true; description adds critical idempotency detail and persistence context. No contradiction.

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?

Well-structured with clear sections: purpose, usage guidelines, side effects, returns. Front-loaded with core action. Every sentence is informative with no redundancy.

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?

Despite no output schema, description details return fields and their importance. Addresses idempotency, linking to list tool, and relationship to invoice tool. Covers all contextual needs for a creation tool with nested parameters.

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 coverage is 100%, so baseline 3. Description adds value by linking returned id to mercury_create_invoice's customerId and clarifying address name requirement. Not a full 5 because schema already documents all parameters.

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?

Description clearly states 'Create a new Accounts Receivable customer (a billable entity you will later invoice)'. Uses specific verb and resource, and distinguishes from sibling tool 'mercury_add_recipient' which handles payment recipients.

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?

Explicitly provides 'USE WHEN' (onboarding before invoice) and 'DO NOT USE' (payment recipients, with alternative named). Also suggests checking mercury_list_customers to avoid duplicates.

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