assign_number

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

With no annotations, the description carries the transparency burden. It thoroughly discloses replacement behavior ('assignment is replaced'), immediate routing, and that the agent uses its configured settings. It does not mention permissions or errors, but covers the core behavioral effects well.

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?

The description is well-structured with a clear opening statement, behavioral details, and an Args list. It is slightly verbose but each sentence adds meaningful detail, earning a high score without being maximally terse.

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 simple two-parameter tool, the description covers purpose, side effects, and parameter sourcing. Since an output schema is indicated, return values need not be described. Minor aspects like ID validation or failure behavior are absent, but overall it is sufficiently complete for an agent to use correctly.

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?

The input schema has zero description coverage, but the description compensates by explaining that phone_number_id is 'the number to configure (from list_numbers)' and agent_id is 'the agent that will answer calls (from list_agents)'. This adds meaning and source references, though without extensive format or constraints.

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 clearly states the tool's action: routing a phone number's inbound calls to an AI agent. It distinguishes itself from the sibling tool unassign_number (opposite action) and explicitly contrasts with make_call for outbound calls.

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?

Provides explicit when-to-use context and clearly states 'This only affects inbound calls. For outbound calls, you specify the agent and number separately in make_call.' This names an alternative tool and gives a clear exclusion, meeting the highest bar.

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