Buy Virtual Number

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

Annotations already declare readOnlyHint=false and idempotentHint=false, so the agent knows this is a mutating, non-idempotent call. The description adds valuable timing context ('Codes typically arrive within ~10-60 seconds'), which annotations don't cover. No contradiction with annotations. Missing disclosure of the financial/cost aspect of a purchase.

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 sentences with zero waste: purpose and returns first, timing second, follow-up routing third. Every sentence earns its place and the most decision-relevant information (what it does, what it returns) is front-loaded.

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 2-parameter purchase tool with no output schema, the description covers purpose, returns, timing, and next steps — nearly complete. The main gap is that it doesn't disclose that this is a paid operation with financial implications, which would be helpful context for an agent.

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% — both service and country have descriptive text in the schema, so the baseline is 3. The description doesn't add parameter-level detail beyond the schema (e.g., it doesn't hint at service code formats or provide examples of common codes), but it doesn't need to since the schema is already complete.

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 (Purchase) and resource (virtual phone number) with a clear purpose (SMS verification), and explicitly names the return values (order_id and phone_number). This distinguishes it from siblings like virtualsms_list_orders (listing) and virtualsms_get_order (retrieval).

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 post-purchase routing: 'Use get_sms to poll for the verification code, or use wait_for_sms to block until it arrives.' This tells the agent what to do next with named sibling tools. However, it does not state when to prefer a rental (create_rental family) over a one-time purchase, or mention cancel_order as a recourse.

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