# x402 AgentUtility D20 Ability Check Resolver

> x402 AgentUtility D20 Ability Check Resolver is a paid API for AI agents from x402.agentutility.ai, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-20).

Resolves a d20 ability check, skill check, attack roll, or saving throw for tabletop RPGs, returning the roll total, success/failure against a DC, and natural-20/natural-1 flags.

## Facts

- Endpoint: POST https://x402.agentutility.ai/ability-check?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-20
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-agentutility-d20-ability-check-resolver-4765520c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_oCAffMvKTfm_bm-YC5j0p

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability x402-agentutility-d20-ability-check-resolver-4765520c -d '<json body>'
```

Example prompt: Roll a d20 with a +5 modifier and advantage against a DC 14 for my ranger's Perception check — tell me if I succeed and whether it was a natural 20.

## When to prefer this

Choose this endpoint when you need a verifiable, auditable, server-side d20 roll with optional modifier and advantage/disadvantage mechanics — especially for AI-driven TTRPG agents where client-side randomness is untrusted, or when you need seedable/reproducible rolls for GMing, testing, or dispute resolution. Prefer it over client-side dice rollers when you need canonical pass/fail adjudication against a DC in an automated workflow.

## Known failure modes

- Invalid modifier type returns a 400 validation error
- DC value out of expected range may return an error
- Missing required fields (e.g. no DC provided) causes a 422 unprocessable entity
- Seed value conflicts or out-of-range inputs may return a 400 error
- Network timeout on the x402 payment layer before the roll is resolved

## How this service works

Resolves a d20 ability check, skill check, attack roll, or saving throw for tabletop RPGs. Rolls a d20 with an optional modifier and advantage/disadvantage, compares to a DC, and reports total, success/failure, and natural-20 / natural-1. Seedable. Use it as a d20 check resolver API for any RPG.

## Output

Returns the raw d20 die value, the final total (die + modifier), whether the total meets or exceeds the DC (success or failure), and boolean flags for natural-20 and natural-1 outcomes. If advantage or disadvantage was applied, both dice values may be included.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "required": [],
     "properties": {
      "dc": {
       "type": "number",
       "description": "Difficulty class to beat. Omit to just get the roll."
      },
      "seed": {
       "type": "number",
       "description": "Optional integer seed for a reproducible roll."
      },
      "modifier": {
       "type": "number",
       "description": "Total bonus/penalty added to the d20 (-20..40). Default 0."
      },
      "advantage": {
       "type": "boolean",
       "description": "Roll twice, take the higher."
      },
      "disadvantage": {
       "type": "boolean",
       "description": "Roll twice, take the lower."
      }
     }
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "dc": {
       "type": "integer"
      },
      "mode": {
       "type": "string"
      },
      "total": {
       "type": "integer"
      },
      "success": {
       "type": "boolean"
      },
      "modifier": {
       "type": "integer"
      },
      "d20_rolls": {
       "type": "array",
       "items": {
        "type": "integer"
       }
      },
      "natural_roll": {
       "type": "integer"
      },
      "critical_failure": {
       "type": "boolean"
      },
      "critical_success": {
       "type": "boolean"
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "dc": 15,
  "mode": "advantage",
  "total": 20,
  "success": true,
  "modifier": 5,
  "d20_rolls": [
   15,
   7
  ],
  "natural_roll": 15,
  "critical_failure": false,
  "critical_success": false
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-agentutility-d20-ability-check-resolver-4765520c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402.agentutility.ai](https://www.zero.xyz/host/x402.agentutility.ai/llms.txt)