VPN.FAIL MCP

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It does mention optional proxy location, browser rendering, screenshots, and CSS wait conditions, which gives some insight. However, it does not explain the default output format, whether the tool returns raw HTML or markdown, or any rate limits/error behavior, leaving notable gaps.

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 a single, front-loaded sentence that efficiently packs the core action and all major optional features. Every word adds value, and there is no redundancy or filler.

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 has 7 parameters, no annotations, but an output schema, the description is moderately complete. It covers the main capabilities but omits important details like parameter meanings for mode/output, default behaviors, and potential side effects. It is adequate but not thorough for a tool of this 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?

The schema has 0% description coverage, so the description must compensate. It adds meaning for country/city (verified exit), wait_for (CSS readiness selector), and screenshot, but leaves mode and output completely unexplained. The mapping between description terms and parameters is partial, so it does not fully compensate for the missing schema descriptions.

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 fetches one URL and lists optional capabilities (verified exit country/city, browser rendering, screenshot, CSS readiness selector). This is a specific verb+resource and distinguishes it from sibling tools like service_status and usage, which deal with monitoring and usage rather than scraping.

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 no guidance on when to use this tool versus alternatives, nor does it mention any exclusions or prerequisites. It simply states what the tool does, leaving the agent to infer usage context. This is a lack of explicit usage 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 for behavioral disclosure. The verb 'Return' implies a read-only operation, but the description does not explicitly state that there are no side effects, whether authentication is needed, or whether the information is cached or real-time. This is only minimally transparent.

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 a single, front-loaded sentence that directly states the tool's purpose. Every word contributes meaning, and there is no redundancy or filler.

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 has no parameters and an output schema is present, the description sufficiently covers the main return items ('proxy inventory' and 'MCP request availability'). The minimal context is acceptable for a simple status check, though it could slightly clarify what 'availability' means.

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 tool has zero parameters, and the schema confirms this. Per the rubric, a baseline of 4 is appropriate when there are no params; there is nothing for the description to add about parameter meaning.

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 ('Return') and identifies the resources ('proxy inventory' and 'MCP request availability'), making the tool's function clear. It does not explicitly compare itself to siblings, but the distinct resource names and tool name differentiate it adequately from 'scrape' and 'usage'.

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 gives no guidance on when to use this tool versus the sibling tools or under what conditions it should be called. It only states what it returns, leaving the agent to infer when to invoke it.

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, the description carries the full burden of behavioral disclosure. 'Return' clearly indicates a read-only operation, and 'anonymous client' implies no authentication. However, it does not mention whether this affects any counters, possible errors, or rate-limit implications. The output schema covers return structure, but additional context on side effects (if any) is missing.

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 a single, concise sentence that front-loads the action ('Return') and specifies the exact data returned. No unnecessary words or repetition; every element adds value.

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?

This is a simple tool with no parameters and an output schema, so the description is largely sufficient. It clearly states what is returned but could be enhanced with a note on typical use cases (e.g., avoiding rate limits) or a pointer to a sibling like 'service_status' for alternative needs. Given the low complexity, the minor gap is acceptable.

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 tool has zero parameters, so schema coverage is trivially 100%. The description does not need to explain parameters as there are none. Baseline for zero parameters is 4, and nothing in the description detracts from this.

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 ('Return') and clearly identifies the resource ('quota usage') with time granularities ('hourly, daily, weekly, and rolling 30-day'). It distinguishes from siblings like 'scrape' and 'service_status' by focusing on usage quota rather than content or service health.

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 the tool is for checking quota usage, but it does not explicitly state when to use it or provide alternatives. Since the sibling tools exist (e.g., 'service_status'), some exclusionary or comparative guidance would improve clarity, but this is not provided.

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