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

Annotations already declare readOnlyHint and non-destructive, so the description earns credit for adding what the annotations do not: the exact data surface returned, the explicit guarantee that 'SIP password and PINs are never returned', and the underlying REST endpoint. That masking note is genuinely useful behavioral context for an agent assembling a response.

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 short sentences with no filler; the returned-field list is front-loaded and the sensitive-field exclusion follows immediately. The trailing 'GET /sip_users/{id}' is mildly redundant but cheap and useful for traceability.

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?

There is no output schema, so enumerating the returned fields (sipuid, extension, caller id, type, linked web user, online state, call settings) is exactly the right compensation, and the security note closes the obvious gap. Only the absence of any usage/error guidance keeps it short of a 5.

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% and the sole parameter is documented there, including the pointer to placetel_list_sip_users as the source of ids. The description adds only 'by id', which restates the schema rather than extending it - baseline 3 applies.

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 retrieval: 'One SIP user (extension) by id', followed by the fields it surfaces. The singular 'one ... by id' scoping implicitly separates it from the list sibling, though it never names placetel_list_sip_users explicitly.

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 by 'by id' - an agent can infer this is the detail lookup after listing. There is no explicit statement of when to use this versus placetel_list_sip_users, nor any prerequisites or error conditions.

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