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

Annotations already declare readOnlyHint/idempotentHint/non-destructive, so the safety profile is covered. The description adds genuine behavioral context: purpose is never refused for novelty (only emptiness), recipient_type is recorded verbatim, and destination country is governed by workspace capabilities rather than by this evaluation — the last point usefully bounds what the tool actually checks.

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?

Three tight sentences, front-loaded with the core action and followed by the two behavioral caveats. Minor redundancy with the schema's own purpose/recipient_type descriptions, but no wasted prose.

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 9-parameter, nested-object tool with no output schema, the description explains inputs but says nothing about what the evaluation returns (verdict format, allow/deny, error signaling), which is the key missing piece an agent needs. Input-side coverage is adequate; outcome-side is absent.

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 only 44%, and the description adds real meaning for purpose, recipient_type, and country. However, five parameters (to, from_number_id, policy, categories, user_authorization) — including the nested policy object — are undocumented in both schema and description, so the gap is not fully compensated.

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 ('Evaluate outbound voice/SMS policy') and anchors it in the workflow ('before creating a call'). It is clearly distinct from create_outbound_call, but it never contrasts itself with the closer sibling authorize_outbound (mentioned only inside a schema property), so sibling differentiation is incomplete.

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?

'before creating a call' implies the timing of use, which is useful, but the description never explicitly names authorize_outbound or check_number_requirements or says when this evaluation is required versus optional. Usage must be inferred rather than stated.

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