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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely new behavioral context: exactly which fields come back and the security guarantee that "SIP passwords and PINs are never returned", which is not derivable from any structured field.

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 front-loaded sentences that lead with the verb and resource, then disclose the return fields and the password guarantee. The trailing "GET /sip_users" is minor low-value filler 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?

There is no output schema, so the description carries the burden of describing the response, and it does enumerate the returned fields (did, caller id, type, online state, registrations) plus the deliberate omissions. Pagination and filter semantics are handled in the schema, so nothing essential is missing, though it never mentions that results can be filtered at all.

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 six filters (did, name, username, description, page, per_page) are already documented; baseline is 3. The description only glosses "extension number (did)", which mildly clarifies the did parameter but adds no syntax or filtering-combination guidance beyond the schema.

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+resource ("List SIP users") and disambiguates the resource by enumerating what a SIP user actually is: phone extensions, softphones, fax and trunk lines. It also names the returned fields, so the agent knows this is the enumeration endpoint rather than the single-record placetel_get_sip_user, though that sibling is never called out by name.

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 says nothing about when to call this versus placetel_get_sip_user or the other list_* siblings, and never mentions the available filters, so an agent gets no routing guidance. The plural "List" implies enumeration, but that is left entirely to inference.

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