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

Annotations declare destructive/non-idempotent/open-world, and the description adds material context beyond them: the call is billed, it requires the calls:write scope, and it does not change carrier settings. That billing and permission disclosure is exactly the kind of cost/authorization detail an agent needs before triggering a mutating, real-world action. It stops short of saying what the call actually produces or how the result is retrieved.

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?

Roughly the first two-thirds of the text is a SIP-family overview covering create/read/change, attach-number, and ownership-check behavior that is not this tool. The identifying sentence arrives late, after content that belongs in sibling descriptions. Substantial pruning would improve selection accuracy.

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 billed, destructive, open-world action with no output schema and four undocumented parameters, key facts are absent: what the test call verifies (e.g., that the agent answers end to end), how to retrieve the outcome via get_sip_connection_test_call, and the meaning of connection_id/project_id. The description covers billing and the ownership prerequisite but leaves the agent unable to predict or follow up on the call's result.

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 50%; to and dial_format are documented in the schema, while number_id, connection_id, agent_id, and project_id are not. The description adds the useful clarification that the call originates from the number (number_id) and that dial_format applies "for this call only," but says nothing about connection_id, agent_id, or project_id. Partial compensation, not full.

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 operative clause is specific: "start_sip_connection_test_call places one billed call (calls:write) from the number to the given phone." However, the first three sentences describe the whole SIP-trunk family (create/read/change connections, attach numbers, ownership checks), so an agent reading only the opening would misidentify this tool as a connection-management operation. Purpose is stated, but buried behind off-topic framing.

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 explicitly separates this tool from its nearest alternatives: check_sip_connection_number_ownership places a verification call, check_sip_connection_reachability sends a SIP OPTIONS probe, and this tool places one billed end-to-end call. It also states the prerequisite that outbound use is refused until ownership is confirmed. It lacks a direct "use this when..." framing, but the comparison is strong enough to route an agent.

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