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

The readOnlyHint annotation already establishes this as a safe read operation. The description adds value by disclosing the return shape (id, name, email, phone) and the intended follow-up tool, which helps the agent understand the result without an output schema. It does not describe pagination or limit behavior, but the schema covers limit.

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 tightly written sentences: the first states what the tool returns and how to search, the second gives the immediate next action. The endpoint path is included without bloating the text.

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?

This is a simple two-parameter read tool with no output schema. The description covers purpose, returned fields, and the follow-up tool, giving the agent everything needed to invoke it correctly despite the absence of an output schema.

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 both parameters are already documented in the schema. The description's '(part of) a name' adds a little intuition for search_string, but it does not add syntax, matching behavior, or other semantics beyond what the schema provides.

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: 'Quick lookup of contacts by (part of) a name', and lists the returned fields. It is clear what the tool does, though it does not explicitly distinguish itself from the similarly named sibling rex_search_contacts.

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 a useful next step ('Use the id with rex_get_contact') and implies this is for quick autocomplete-style lookup. However, it does not state when to use this instead of rex_search_contacts or other contact-related siblings, leaving the alternative choice implicit.

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