list_countriesFind countries where phone numbers are available for purchase. Filter by service to see only matching options, with configurable result limits.
List countries that currently have buyable numbers. Optionally filter to a single service.
| Name | Required | Description | Default |
|---|---|---|---|
| limit | No | Max countries to list (default 60). | |
| service | No | Service code to filter countries by, e.g. "tg". |
Changes observed during successful MCP inspections.
v0.1.1Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds the useful context that results reflect current buyable-number availability, but it does not reveal additional behavioral traits such as result ordering, pagination behavior, or the meaning of an empty response.
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?
A single front-loaded sentence states the core purpose and the optional filter with no wasted words. It is concise and structured effectively for quick agent comprehension.
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 read-only list tool with 100% schema coverage and readOnly/openWorld annotations, the description plus schema provide sufficient context. The only minor gap is not explicitly directing users to list_services for service codes, though the 'service' schema example partly mitigates this.
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%, with both 'limit' and 'service' documented. The description only reiterates the optional service filter without adding meaning beyond the schema, so the baseline score of 3 is appropriate.
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 uses a specific verb ('List'), a clear resource ('countries'), and a meaningful qualifier ('that currently have buyable numbers'). It also distinguishes itself from siblings like list_services by focusing on countries and availability.
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 implies its usage: call it when you need available countries, and optionally narrow by service. However, it does not explicitly state when to prefer an alternative or mention related tools like list_services for resolving service codes.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.