purchasePhoneNumber

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

Beyond the annotations (readOnlyHint=false, destructiveHint=true), the description discloses the financial impact ('monthly rental comes out of your wallet') and the state change ('number is added to your account'). It does not mention irreversibility or refund policy, but the key behavioral consequences are present and consistent with annotations.

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 two substantive sentences are concise and front-loaded with the operation and its effects. The parenthetical 'Tags: Phone numbers' is minor non-functional metadata that keeps it from a perfect score.

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?

The tool has no output schema, but the description plus fully-covered schema gives an agent enough to invoke it correctly: the purchase source, cost, resulting account state, and the required/nested request body are all accounted for. The only notable gap is the lack of explicit coordination with search and import siblings, which is already reflected in the usage-guidelines score.

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%, so the parameters are already well-documented in the schema (region enum, phone_number 'as returned by the search operation', Idempotency-Key for safe retries). The description adds no new parameter-level meaning, which matches the baseline for high coverage.

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 opens with 'Buy a phone number from the OmniDimension number shop', naming the verb, resource, and source. It also states the consequences (monthly rental, added to account, attach to agent), which distinguishes it from sibling import tools like importTwilioNumber.

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 shop provenance and 'ready to attach' imply when to use it, but there is no explicit statement of when not to use it or which alternatives to prefer. For instance, it does not tell the agent to call searchPhoneNumbers first or to use importTwilioNumber/importExotelNumber for externally hosted numbers.

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