DropEngine x402 Agent Services

check_change

Paid Change / Diff Check ($0.001 USDC). Checks normalized text on a public HTTPS page against a previous SHA-256 hash, returning a compact diff when a prior snapshot is available.

Agent entry points: risky external action → use Agent Action Gate when a combined action-specific safety assessment is needed; unclear capability/provider → use free /api/discover; constrained comparison between callable alternatives → use paid route_tool; known single capability → call the direct tool; multi-step objective → read the matching workflow recipe and call only relevant steps. Workflows are stateless recipes, not executors; calls are paid separately and are not bundle charged. Agent Action Gate does not approve payment, sign or broadcast transactions, evaluate seller reputation, replace transaction simulation, replace route_tool, or replace human approval.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`url`	Yes
`previous_hash`	Yes

Output Schema

TableJSON Schema

Name	Required	Description	Default
`diff`	Yes
`meta`	No
`next`	No
`error`	No
`cached`	Yes
`result`	No
`status`	No
`changed`	Yes
`payment`	No
`success`	Yes
`summary`	Yes
`agent_ux`	No
`checked_at`	Yes
`change_type`	Yes
`change_score`	Yes
`current_hash`	Yes
`previous_hash`	Yes
`data_age_seconds`	Yes
`baseline_available`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed7 schema fields changedOct 8, 2026

addedOutput schema / properties / agent_ux

Added value: +{
+  "additionalProperties": false,
+  "properties": {
+    "error": {
+      "anyOf": [
+        {},
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "meta": {
+      "additionalProperties": {},
+      "propertyNames": {
+        "type": "string"
+      },
+      "type": "object"
+    },
+    "next": {
+      "items": {},
+      "type": "array"
+    },
+    "payment": {
+      "additionalProperties": false,
+      "properties": {
+        "execution_status": {
+          "enum": [
+            "not_started",
+            "succeeded",
+            "failed",
+            "unknown"
+          ],
+          "type": "string"
+        },
+        "status": {
+          "enum": [
+            "not_required",
+            "required",
+            "settled",
+            "failed",
+            "unknown"
+          ],
+          "type": "string"
+        }
+      },
+      "required": [
+        "status",
+        "execution_status"
+      ],
+      "type": "object"
+    },
+    "result": {},
+    "status": {
+      "enum": [
+        "succeeded",
+        "failed",
+        "partial",
+        "outcome_unknown"
+      ],
+      "type": "string"
+    }
+  },
+  "required": [
+    "status",
+    "result",
+    "error",
+    "meta",
+    "payment",
+    "next"
+  ],
+  "type": "object"
+}

addedOutput schema / properties / error

Added value: +{
+  "anyOf": [
+    {},
+    {
+      "type": "null"
+    }
+  ]
+}

addedOutput schema / properties / meta

Added value: +{
+  "additionalProperties": {},
+  "propertyNames": {
+    "type": "string"
+  },
+  "type": "object"
+}

addedOutput schema / properties / next

Added value: +{
+  "items": {},
+  "type": "array"
+}

addedOutput schema / properties / payment

Added value: +{
+  "additionalProperties": false,
+  "properties": {
+    "execution_status": {
+      "enum": [
+        "not_started",
+        "succeeded",
+        "failed",
+        "unknown"
+      ],
+      "type": "string"
+    },
+    "status": {
+      "enum": [
+        "not_required",
+        "required",
+        "settled",
+        "failed",
+        "unknown"
+      ],
+      "type": "string"
+    }
+  },
+  "required": [
+    "status",
+    "execution_status"
+  ],
+  "type": "object"
+}

addedOutput schema / properties / result
```
Added value: +{}
```

addedOutput schema / properties / status

Added value: +{
+  "enum": [
+    "succeeded",
+    "failed",
+    "partial",
+    "outcome_unknown"
+  ],
+  "type": "string"
+}

Changed1 schema field changedSep 29, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "additionalProperties": false,
+  "properties": {
+    "baseline_available": {
+      "type": "boolean"
+    },
+    "cached": {
+      "type": "boolean"
+    },
+    "change_score": {
+      "type": "number"
+    },
+    "change_type": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "changed": {
+      "type": "boolean"
+    },
+    "checked_at": {
+      "type": "string"
+    },
+    "current_hash": {
+      "type": "string"
+    },
+    "data_age_seconds": {
+      "type": "number"
+    },
+    "diff": {
+      "anyOf": [
+        {
+          "additionalProperties": false,
+          "properties": {
+            "added": {
+              "items": {
+                "type": "string"
+              },
+              "type": "array"
+            },
+            "removed": {
+              "items": {
+                "type": "string"
+              },
+              "type": "array"
+            }
+          },
+          "required": [
+            "added",
+            "removed"
+          ],
+          "type": "object"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    },
+    "previous_hash": {
+      "type": "string"
+    },
+    "success": {
+      "const": true,
+      "type": "boolean"
+    },
+    "summary": {
+      "additionalProperties": false,
+      "properties": {
+        "price_changed": {
+          "type": [
+            "boolean",
+            "null"
+          ]
+        },
+        "stock_changed": {
+          "type": [
+            "boolean",
+            "null"
+          ]
+        }
+      },
+      "required": [
+        "price_changed",
+        "stock_changed"
+      ],
+      "type": "object"
+    }
+  },
+  "required": [
+    "success",
+    "changed",
+    "baseline_available",
+    "current_hash",
+    "previous_hash",
+    "change_score",
+    "change_type",
+    "diff",
+    "summary",
+    "cached",
+    "data_age_seconds",
+    "checked_at"
+  ],
+  "type": "object"
+}

First observedSep 28, 2026

TDQS

B3.3/5.0

Behavior3/5

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

With no annotations, the description carries the full burden, and it does disclose real traits: paid at $0.001 USDC, requires a public HTTPS page, calls are billed separately and not bundle-charged, and the diff is returned only 'when a prior snapshot is available'. It omits what happens when no snapshot exists, payment authorization mechanics, and error behavior, so it is partial rather than thorough.

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

Conciseness3/5

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

The first sentence is tight and front-loaded with the cost and the action. The following block is long generic boilerplate about Agent Action Gate, /api/discover, route_tool and workflow recipes that is largely irrelevant to invoking this specific tool, and its list of 'does not...' exclusions is repetitive.

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

Completeness3/5

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

An output schema exists, so return-value explanation is not needed, and the description does cover cost, the public-HTTPS precondition, and the conditional diff. With 0% schema coverage on both required params and no annotations, the edge cases (no prior snapshot, hash mismatch, payment failure) are left unspecified for a paid tool.

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 description coverage is 0%, so the description must compensate. It adds meaning to both params: the url must be a public HTTPS page, and previous_hash is a SHA-256 hash. That is genuinely useful, but it does not cover format/length constraints or failure modes for a stale or mismatched hash.

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?

The first sentence gives a specific verb+resource: 'Checks normalized text on a public HTTPS page against a previous SHA-256 hash, returning a compact diff'. This is a clear, concrete capability. It stops short of naming the neighbouring siblings it is distinct from (check_url, scan_content), so it lands at 4 rather than 5.

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

Usage Guidelines3/5

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

The 'Agent entry points' block gives generic meta-routing ('known single capability → call the direct tool', 'multi-step objective → read the recipe'), but never states when to pick check_change over check_url or scan_content, nor the precondition that a prior snapshot must exist to get a diff. Usage is implied rather than instructed.

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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