xpay✦ MCP Server

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

With no annotations, the description carries the full burden. The phrasing 'Check' and 'Shows' implies a read-only operation, and the top-up URL provides useful context. However, it does not disclose whether the balance is real-time, cached, or whether authentication is required, leaving some behavioral unknowns.

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, front-loaded with the primary action, and every word adds value. It avoids fluff and stays well within appropriate size.

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 0-parameter tool with no annotations and no output schema, the description covers the core functionality, the meaning of the balance, and the follow-up action to top up. It lacks explicit return format or refresh semantics, but these are minor for a balance check tool.

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 the baseline is 4. The description adds meaning by explaining that the balance represents 'available credits for running services', which gives semantic context beyond the empty parameter schema.

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 'Check' and names the exact resource 'XPay wallet balance', clearly distinguishing it from sibling tools like xpay_details and xpay_discover. The added context 'Shows available credits for running services' further clarifies the tool's purpose.

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 by stating it shows available credits for running services and suggests topping up if balance is low, but it does not explicitly mention when to use this tool versus alternatives like xpay_details or xpay_run. No exclusion criteria are provided.

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 handles transparency by stating it retrieves information without executing anything. The phrase 'Then use xpay_run to execute' implies this tool is read-only. It doesn't disclose error handling or authentication, but for a details tool, the core behavior is adequately conveyed.

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 three sentences, front-loaded with purpose, then usage guidance, then next step. Every sentence carries meaning with no filler or repetition of schema details.

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 one-parameter tool with no output schema, the description fully explains what the tool returns and its position in the workflow. No additional context is needed for an agent to select and invoke it correctly.

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 one required parameter, slug, with a description that already explains its origin ('Server slug from discover results'). The tool description adds context by mentioning xpay_discover, but this is minimal extra value. Baseline of 3 is appropriate given the schema covers all 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 tool returns the full tool list, input schemas, and pricing for an XPay server. It explicitly distinguishes itself from siblings by mentioning xpay_discover and xpay_run, making the specific resource and action unambiguous.

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 usage context: 'Use after xpay_discover' and 'Then use xpay_run to execute a specific tool.' This clearly sequences the tool relative to its siblings, indicating when to use it and what to do next.

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 burden. It discloses what the tool returns (matching servers with slugs, tool counts, pricing) and its proactive nature. It does not mention rate limits or auth, but for a read-only search tool, this is sufficient and adds value beyond the schema.

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 well-structured and efficient: purpose first, then usage triggers, return info, and a pointer to the next step. The list of use cases is long but purposeful, not fluff. Every sentence earns its place.

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 simplicity (3 params, no output schema), the description covers purpose, when to use, return content, and relationship to xpay_details. It is complete enough for an agent to invoke correctly, though it could have briefly explained what 'servers' are in this context.

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 baseline is 3. The description adds value by providing natural language query examples (e.g., 'research a company', 'find contact emails') and clarifying the return structure, which helps understand the query and limit parameters. Not a full substitute, but a clear enhancement.

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 searches XPay Hub for paid API services, with a specific verb and resource. It distinguishes itself from siblings by listing concrete use cases and pointing to xpay_details as the next step for viewing a server's full tool list.

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 proactive usage guidance with a comprehensive list of scenarios (search web, find emails, enrich contacts, etc.). It also tells the user to follow up with xpay_details, marking a clear workflow. No alternatives are named, but the context is unambiguous.

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 the full burden. It discloses automatic cost deduction and mandates copying the exact cost/balance line from the result footer. This is significant behavioral context beyond basic execution, though it does not cover failure modes or side-effect specifics.

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 somewhat long but every sentence earns its place, especially the CRITICAL billing receipt instruction which is essential for correct assistant behavior. The main action is front-loaded and the workflow is logically ordered. Slight verbosity around the 'CRITICAL' block prevents a 5.

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 executes arbitrary tools, and the description covers the essential context: prerequisite discovery, cost deduction, and the mandated receipt handling. Given the absence of an output schema and the variable nature of results, this is a complete description for real-world use. It could mention error handling, but that is minor.

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 descriptions cover all three parameters with meaningful guidance: slug from xpay_discover, tool from xpay_details, and arguments as key-value pairs. The description adds an example for arguments but does not go beyond the schema. Baseline 3 is appropriate given the 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 opens with 'Execute any tool on any XPay server', a specific verb+resource statement that clearly distinguishes this tool from siblings like xpay_balance, xpay_details, and xpay_discover. It unambiguously identifies this as the general-purpose execution tool.

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 workflow guidance: 'Use xpay_discover to find servers and xpay_details to check required inputs before running.' This tells the agent when to use prerequisite tools and implies xpay_run is for after discovery and validation. No exclusions are needed for a generic executor.

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