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

With no annotations provided, the description carries full behavioral disclosure. It discloses that phone numbers are normalized to E.164, which is a behavioral trait not inferable from the schema alone (though the schema does mention it). It does not contradict any annotations since none exist.

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?

Two sentences with no wasted words. The purpose is stated first, followed by the key constraint and a normalization note. Every sentence earns its place.

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?

The description is adequate for a simple create operation but lacks information about the return value or any side effects beyond what the schema mentions. With no output schema, the agent does not know what the response contains (e.g., contact ID). For a create tool, this is a notable gap.

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?

The description adds a critical piece of semantics beyond the schema: the requirement that at least one of first_name, last_name, or email must be provided. This is not present in the schema (required: 0). It also reiterates phone normalization, though the schema already covers that. For other parameters, the schema already provides descriptions, so the description doesn't add much there.

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 verb and resource ('Create a new contact') and immediately clarifies a key constraint (at least one of first_name/last_name/email). This distinguishes it clearly from contacts_update, contacts_delete, and other contact tools, which are not ambiguous.

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?

The description provides explicit usage guidance by specifying the minimum required fields, which tells the agent when this tool is appropriate (when at least one of those fields is available). It does not explicitly name alternatives or exclusions, but the context is clear enough for a create tool.

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