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

Annotations only declare readOnlyHint=false, destructiveHint=false, and openWorldHint=false. The description adds real behavior beyond that: the number's downstream effect (it is what rings on human handoff), the default ownership scope, and the manager-level authorization path. It doesn't cover validation failures or whether an existing number is overwritten, which keeps it off a 5.

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, zero filler. The core effect of the tool is front-loaded, and the ownership/permission detail follows as the second clause.

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?

For a two-parameter tool with full schema coverage, annotations, and no output schema, the description covers purpose, default scope, authorization, and the sibling reference that supplies user_id. The only gap is what the call does to any previously set number, which an agent could reasonably want to know before calling.

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%, so the format details (E.164 or 10-digit US) are already documented and the baseline is 3. The description adds meaning the schema lacks: user_id carries an authorization implication (managers only) and a provenance hint (from list_team), which changes how an agent should populate it.

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 ('Set the mobile') and immediately clarifies the effect — it's the number that rings when the crew hands off to a human via get_a_human. That distinguishes it from number-related siblings like buy_number and search_numbers without the agent needing to open another schema.

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?

Gives clear context for the optional parameter: default scope is the caller's own number, and managers can target a teammate using user_id sourced from list_team. It doesn't state exclusions or failure conditions (e.g., what happens if the caller isn't a manager), so it stops short of full when/when-not guidance.

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