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

With no annotations provided, the description carries full burden and does well by disclosing key behavioral traits: it's a read operation (implied by 'List'), returns ISO 3166-1 alpha-2 country codes, and mentions the 190+ country support scope. It doesn't mention rate limits, authentication needs, or pagination, but provides solid context for a listing tool.

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?

Two sentences with zero waste: first sentence states purpose and scope, second sentence specifies return format. Every word earns its place, and information is front-loaded appropriately for a simple tool.

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 listing tool with one optional parameter and no output schema, the description provides good completeness: purpose, scope, return format, and service context. It could benefit from mentioning when to use versus siblings, but covers the essential context given the tool's low complexity.

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 schema already fully documents the single optional parameter with its enum values and default. The description doesn't add any parameter-specific information beyond what's in the schema, meeting the baseline expectation for high schema 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 clearly states the verb ('List') and resource ('available proxy exit countries'), specifies the service ('Apollo'), and distinguishes from siblings by focusing on country listing rather than fetching or status checking. It provides specific scope information (190+ countries, residential proxy exits).

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 usage context (when you need to know available proxy exit countries) but doesn't explicitly state when to use this tool versus the sibling tools (proxy_fetch, proxy_status). No explicit alternatives or exclusions are provided, leaving usage decisions to inference.

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

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

With no annotations provided, the description carries full burden and does an excellent job disclosing key behavioral traits: cost ($0.005/request), max response size (250KB), rate limits (100 req/min), and capabilities (supports 190+ countries, rotating/sticky sessions, handles anti-bot protection). It doesn't mention error handling or response format details.

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 description is perfectly sized and front-loaded, starting with the core purpose, then listing key capabilities, and ending with operational constraints. Every sentence earns its place with zero wasted words, making it highly efficient for 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 tool with no annotations and no output schema, the description provides excellent coverage of behavioral aspects (cost, limits, capabilities). However, without an output schema, it doesn't describe what the tool returns (response format, error structure), leaving a gap in complete understanding of the tool's interface.

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%, providing comprehensive parameter documentation. The description adds minimal parameter semantics beyond the schema, only implying the URL parameter through 'fetch any URL' and mentioning country support. Baseline score of 3 is appropriate when schema does the heavy lifting.

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 clearly states the tool's purpose with specific verbs ('fetch any URL') and resources ('through Apollo's residential proxy network'), distinguishing it from sibling tools like list_countries and proxy_status which likely provide metadata rather than performing actual fetching operations.

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 provides clear context about when to use this tool (fetching URLs through proxy with specific capabilities), but doesn't explicitly state when NOT to use it or mention alternatives to this tool. It distinguishes from siblings by function but lacks explicit exclusion guidance.

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

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

No annotations are provided, so the description carries the full burden. It discloses that the tool checks 'availability, pricing, and limits,' which are key behavioral traits. However, it doesn't specify details like response format, error handling, or whether it requires authentication, leaving some gaps in transparency.

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 description is two sentences with zero waste: the first states the purpose, and the second provides usage guidelines. It is front-loaded with essential information and appropriately sized for the tool's simplicity.

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?

Given the tool's low complexity (0 parameters, no output schema, no annotations), the description is mostly complete. It covers purpose and usage well, but lacks details on output format or error behavior, which could be helpful despite the simplicity.

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?

The input schema has 0 parameters with 100% coverage, so no parameter documentation is needed. The description adds value by explaining the tool's purpose and usage, which compensates for the lack of parameters, aligning with the baseline for zero parameters.

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 clearly states the specific action ('Check') and the resource ('Apollo proxy service availability, pricing, and limits'), making the purpose explicit. It distinguishes this tool from sibling tools like 'list_countries' and 'proxy_fetch' by focusing on service status verification rather than data retrieval or operations.

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 provides explicit guidance on when to use this tool: 'Use this to verify the service is online before making requests.' This directly tells the agent to invoke it as a prerequisite check before using other tools, offering clear context and distinguishing it from alternatives.

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