CrossingKey MCP

Purchase Prompt Heuristic Audit

prompt.audit

Idempotent

PAID $0.01 USDC on Base via x402. Scores selected prompt structure signals using deterministic heuristics. Calling this MCP tool returns a payment challenge and does not autonomously spend funds.

Input Schema

Name	Required	Description	Default
`text`	Yes	Input text, maximum 65536 UTF-8 bytes.

Output Schema

Name	Required	Description	Default
`asset`	No
`error`	No
`input`	No
`price`	No
`pay_to`	No
`status`	No
`accepts`	No
`network`	No
`resource`	No
`capability`	No
`extensions`	No
`purchaseId`	No
`instruction`	No
`x402Version`	No
`entitlementId`	No
`execution_url`	No
`execution_mode`	No
`payment_required`	No
`payment_required_header`	No
`settlement_expectations`	No
`confirmation_expectations`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed10 schema fields changedOct 15, 2026

changedOutput schema / additionalProperties
```
Previous value: -falseNew value: +true
```

addedOutput schema / properties / accepts

Added value: +{
+  "items": {
+    "additionalProperties": true,
+    "properties": {},
+    "type": "object"
+  },
+  "type": "array"
+}

addedOutput schema / properties / entitlementId
```
Added value: +{
+  "type": "string"
+}
```
addedOutput schema / properties / error
```
Added value: +{
+  "type": "string"
+}
```

addedOutput schema / properties / extensions

Added value: +{
+  "additionalProperties": true,
+  "properties": {},
+  "type": "object"
+}

addedOutput schema / properties / purchaseId
```
Added value: +{
+  "type": "string"
+}
```

addedOutput schema / properties / resource

Added value: +{
+  "additionalProperties": true,
+  "properties": {},
+  "type": "object"
+}

addedOutput schema / properties / status
```
Added value: +{
+  "type": "string"
+}
```

addedOutput schema / properties / x402Version

Added value: +{
+  "const": 2,
+  "type": "number"
+}

removedOutput schema / required

Removed value: -[
-  "payment_required",
-  "execution_mode",
-  "capability",
-  "input",
-  "price",
-  "asset",
-  "network",
-  "pay_to",
-  "execution_url",
-  "payment_required_header",
-  "settlement_expectations",
-  "confirmation_expectations",
-  "instruction"
-]

AddedOct 10, 2026

TDQS

A3.5/5.0

Behavior4/5

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

Adds substantial context beyond annotations: the $0.01 USDC on Base cost, the x402 rail, that calling returns a payment challenge, and that it does not autonomously spend funds. This directly addresses the auth/payment dimension that readOnlyHint=false implies but does not explain.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three tight fragments with no waste; the payment cost and the purpose both land up front, followed by the critical no-auto-spend caveat. Efficient for the information conveyed.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists so return values need no explanation, and the payment/challenge behavior is covered. The only real gap is routing guidance against the numerous sibling audit tools, but the core call contract is complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% for the single 'text' parameter, so the schema already documents format and the 65536-byte limit. The description adds no syntax or constraint detail beyond it, making the baseline 3 correct.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource: 'Scores selected prompt structure signals using deterministic heuristics.' The 'prompt' qualifier distinguishes it from the many other audit siblings (mcp.schema_audit, openapi.quality_audit), though it never names or contrasts those siblings directly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No statement of when to use this versus the other audit tools, and no prerequisites beyond the payment behavior. The agent learns the cost and challenge flow but nothing about appropriate contexts or alternatives.

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

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