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

Annotations already declare readOnlyHint=false, openWorldHint=true, idempotentHint=false, and destructiveHint=false. The description adds genuinely useful context beyond them by clarifying that no message is dispatched to the contact and by naming the underlying endpoint, which tells the agent this is a silent record write rather than a messaging action.

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 short fragments, front-loaded with the operation class and the core action, with nothing padded. The trailing endpoint reference adds little for an agent but costs only a few tokens.

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?

As a creation tool with annotations but no output schema, the description covers the essential what and the key non-obvious behavior (no message sent). It omits what is returned on success and whether re-posting the same phone number creates a duplicate or returns the existing contact, which is notable given idempotentHint=false.

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 all five parameters are already documented in the schema with formats, lengths, and patterns. The description contributes no additional parameter meaning, so the baseline 3 is appropriate.

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 a contact (customer) to the Textline address book', which an agent can easily separate from textline_get_customer and textline_update_customer. The 'WRITE:' prefix reinforces the operation class, though it does not explicitly contrast with the closest siblings.

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?

Usage is only implied: the WRITE label and 'add' verb indicate a creation operation. There is no explicit statement of when to prefer this over textline_update_customer, nor any prerequisite such as required permissions or how duplicates by phone number are handled.

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