DropEngine x402 Agent Services

simulate_transaction

Paid Transaction Preflight ($0.02 USDC on Base). Simulates an unsigned Base transaction before an autonomous agent signs or broadcasts it. Returns RPC execution/revert status, gas estimate, known top-level method decoding, direct ERC-20 transfer/approval calldata, unlimited approval warnings, and machine-readable risk. Standard JSON-RPC does not expose full internal token state changes; do not treat calldata decoding as a complete state diff. Never send a private key or seed phrase. This tool never signs, holds keys, or broadcasts.

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
`to`	Yes
`data`	Yes
`from`	Yes
`chain`	Yes
`value`	Yes

Output Schema

TableJSON Schema

Name	Required	Description	Default
`meta`	No
`next`	No
`chain`	Yes
`error`	No
`cached`	Yes
`result`	No
`status`	No
`payment`	No
`success`	Yes
`agent_ux`	No
`chain_id`	Yes
`degraded`	Yes
`warnings`	Yes
`approvals`	Yes
`checked_at`	Yes
`risk_level`	Yes
`risk_score`	Yes
`estimated_gas`	Yes
`gas_price_wei`	Yes
`revert_reason`	Yes
`analysis_scope`	Yes
`contract_calls`	Yes
`recommendation`	Yes
`simulated_block`	Yes
`token_transfers`	Yes
`estimated_usd_cost`	Yes
`simulation_success`	Yes
`contract_reputation`	Yes
`estimated_native_cost`	Yes
`native_balance_changes`	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"
+}

First observedSep 28, 2026

TDQS

A4/5.0

Behavior5/5

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

With no annotations, the description carries the full burden and does so well: it enumerates the returned signals (revert status, gas estimate, method decoding, ERC-20 transfer/approval calldata, unlimited-approval warnings, machine-readable risk), discloses a hard limitation (no full internal token state diff), and states the safety contract (never signs, holds keys, or broadcasts; never send a private key).

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 paragraph is dense and well front-loaded, but the 'Agent entry points' paragraph is generic cross-tool routing boilerplate that is not specific to this tool and repeats the same 'does not replace...' caveat twice, diluting focus.

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?

Return values are covered by the output schema and the description redundantly restates them; safety and limitations are well covered. The gap is parameter-level semantics for 5 undocumented required fields, which the schema alone does not explain.

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

Parameters2/5

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

Schema description coverage is 0% across 5 required parameters, and the description adds no per-parameter meaning for chain, from, to, value, or data. It implies 'unsigned transaction' and mentions ERC-20 calldata decoding, but an agent still gets no guidance on the value units, data encoding expectations, or chain field values beyond the schema enum.

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

Purpose5/5

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

States a precise verb+resource+scope: simulates an unsigned Base transaction before signing/broadcasting. It is clearly distinguishable from sibling audit/simulation tools (token_security_audit, preflight_action) and names the paid cost and chain up front.

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

Usage Guidelines4/5

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

The 'Agent entry points' block gives an explicit routing map (risky external action -> Agent Action Gate, unclear capability -> discover, comparison -> route_tool, known capability -> direct tool) and states what this tool does not replace. However, it never states directly when to prefer simulate_transaction over close siblings like preflight_action.

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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