xpay✦ MCP Server

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

With no annotations, description carries full burden. It discloses the tool shows available credits and references external top-up URL, but omits caching behavior, error scenarios, or return value structure.

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?

Three sentences with zero waste: purpose (check balance), context (credits for services), and action (top-up URL). Information is front-loaded and 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?

Adequate for a simple read-only tool with no output schema. Mentions return concept ('Shows available credits') and external dependency, though could specify return format (number vs object).

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?

Tool has zero parameters (empty schema), meeting the baseline score of 4. Description correctly implies no inputs are needed to retrieve balance.

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?

Description uses specific verb 'Check' with resource 'XPay wallet balance' and distinguishes from siblings by specifying this returns 'credits for running services' (unlike xpay_discover, xpay_run, or xpay_details).

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 clear context that balance is needed for 'running services' and includes actionable remediation ('Top up at hub.xpay.sh if balance is low'). Lacks explicit contrast with siblings (e.g., 'use before xpay_run'), though implied.

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 what data is returned (full tool list, schemas, pricing), compensating for the missing output schema. However, it lacks explicit statements about safety (read-only nature), idempotency, or error conditions that annotations would typically cover.

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?

Three sentences with zero waste: sentence 1 states purpose, sentence 2 specifies when to use, sentence 3 indicates next steps. Information is perfectly front-loaded and structured 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 single-parameter lookup tool, the description is complete. It compensates for the lack of output schema by detailing the return structure (tools, schemas, pricing) and contextualizes the tool within the sibling workflow (discover→details→run). Minor gap: explicit safety characteristics due to missing annotations.

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 coverage is 100% with detailed description and examples for the 'slug' parameter. The description implicitly references the target by mentioning 'for an XPay server,' aligning with the parameter's purpose, but does not explicitly discuss the parameter. Baseline 3 is appropriate given the schema's completeness.

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?

Description uses specific verb 'Get' with clear resources (tool list, input schemas, pricing) and scope (XPay server). It explicitly distinguishes this from siblings by positioning it between xpay_discover and xpay_run in the workflow.

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 sequencing: 'Use after xpay_discover' establishes prerequisites, and 'Then use xpay_run' indicates the next step. This clearly defines when to use the tool versus its alternatives/siblings.

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 provided, so description carries full burden. It discloses return values ('Returns matching servers with slugs, tool counts, and pricing') and workflow position. Could improve by explicitly stating read-only/safety nature, but 'Search' implies non-destructive behavior adequately.

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?

Well-structured with four distinct sentences covering purpose, usage triggers, return values, and next-step workflow. The proactive task list is long but necessary to convey broad applicability. Minor deduction for density of the list, but every element serves a purpose.

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?

No output schema exists, so description compensates by detailing return format (servers with slugs/pricing). No annotations exist, but tool behavior is clear. Mentions sibling relationship for workflow completeness. Fully adequate for a discovery tool with 3 parameters.

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 coverage is 100% with detailed parameter descriptions (including enum semantics for 'type' and examples for 'query'). The description adds no parameter-specific guidance, but with complete schema coverage, baseline 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?

Opens with specific verb 'Search' and resource 'XPay Hub for paid API services.' The title 'Discover' combined with description clearly positions this as a discovery/search tool, distinguishing it from sibling xpay_run (execution) and xpay_details (deep inspection).

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?

Explicitly states 'Use this PROACTIVELY when the user asks you to:' followed by comprehensive task examples (web search, email finding, etc.). Critically, it names the specific sibling alternative 'Use xpay_details next to see the full tool list,' creating a clear workflow chain.

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 and successfully discloses critical behavioral traits: automatic cost deduction from wallet and the mandatory output format requiring the billing receipt footer. Missing only error handling or idempotency details to reach a 5.

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?

Four well-structured sentences progress logically: purpose → billing behavior → prerequisites → critical output constraint. Every sentence earns its place; the example billing line in the final sentence is necessary specificity rather than verbosity.

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 complex meta-tool with no output schema, the description adequately covers the unique wrapper behavior (billing, result formatting) and cross-tool workflow. A 5 would require additional detail on error states or retry behavior, but the critical post-execution requirement is well-documented.

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%, establishing a baseline of 3. The description references xpay_details for input requirements rather than repeating parameter semantics, which is appropriate given the schema's completeness and the tool's nature as a generic executor.

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 the specific action 'Execute any tool on any XPay server,' clearly defining the verb and resource. It effectively distinguishes from siblings (xpay_discover for finding servers, xpay_details for checking inputs) by stating this is the execution step.

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 establishes clear prerequisites and when to use sibling tools versus this one, creating a logical sequence.

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