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 useful behavior beyond that: deterministic ordering (oldest first), the cursor-based paging contract, and the semantics of `total` (size of the whole list, not the page). The parenthetical "tags (up to 20)" is slightly ambiguous about whether it limits tags per contact or fields returned.

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?

One dense sentence plus two short clauses; ordering and pagination are front-loaded and the GraphQL query name trails as a useful appendix. No filler, and every clause carries information the agent needs.

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?

With no output schema, the description does the work of enumerating the returned fields, the flag set, ordering, and the meaning of `total`, so the agent can use the response without guessing. Minor residual gaps: no mention of default page size behavior in prose (it is in the schema) and no scoping/auth notes for an openWorldHint tool.

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 `after` and `page_size` are already fully documented, which sets a baseline of 3. The description adds value by tying `after` to the previous reply's next_cursor as a paging flow and by defining `total` relative to the unpaged list, clarifying how the two parameters interact with the response.

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 ("List the SMS contacts (the subscriber list)") and immediately enumerates the returned fields, so the agent knows exactly what it gets back. It is clearly distinguished from the singular siblings superphone_get_contact and superphone_find_contact by being a bulk list of the whole subscriber base.

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 makes clear this returns the full list (oldest first) and explains the pagination loop via next_cursor, which is the main usage decision for this tool. It stops short of explicitly routing away from find_contact or get_contact when a specific record is wanted, leaving that inference to the agent.

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