# Synthex Forge MCP Eval Judge

> Synthex Forge MCP Eval Judge is a paid API for AI agents from x402.synthexforge.com, paid per call via x402, $0.15/call, status unknown (last checked 2026-10-23).

Grades a candidate LLM response against a multi-criterion rubric, returning a scored evaluation artifact signed with Ed25519 and SHA-256 on-chain via x402

## Facts

- Endpoint: POST https://x402.synthexforge.com/v1/mcp/eval/judge?utm_source=zero.xyz
- Price: $0.15/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-23
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/synthex-forge-mcp-eval-judge-196e21ed
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_G1fnWMgVCWkeZE87hKXte

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 synthex-forge-mcp-eval-judge-196e21ed -d '<json body>'
```

Example prompt: Grade this model response against my rubric: rubric has two criteria — fact-presence (weight 0.6, target 'Paris is the capital of France') and length-window (weight 0.4, min_len 20, max_len 200) — and the candidate answer is 'Paris, the capital of France, is known for the Eiffel Tower.' with reference 'Paris is the capital of France.' Label the job 'capital-city-eval'.

## When to prefer this

Choose this endpoint when you need a cryptographically attested, rubric-based evaluation of LLM outputs — especially for governance, compliance audit trails, or multi-criterion grading where the signed artifact matters. Prefer it over plain text diff tools or simple similarity APIs when you need provable, on-chain attestation of the eval result, or when you require flexible criterion types (token-overlap, exact-match, fact-presence, length-window, keyword-presence) in a single call.

## Known failure modes

- Missing required response_pair field returns a 400 validation error
- Malformed rubric array (missing kind or weight) may produce partial scores or a 422
- Payment not settled causes HTTP 402 with x402 v2 payment-required envelope before processing
- Invalid or unsupported criterion kind (e.g. typo) may cause criterion to be skipped or error
- Empty candidate text may yield a zero score without error
- Network or chain issues may delay attestation signing

## How this service works

Synthex Forge x402 Receive: 41 paid verification, attestation and governance endpoints (Ed25519 + SHA-256 signed artifacts) plus free verify/public-key/standard sibling routes. Paid routes answer HTTP 402 with an x402 v2 `payment-required` envelope (atomic USDC on Base mainnet, chain ID 8453). Free routes are declared with `security: []` per the x402scan discovery spec.

## Output

A JSON object containing an overall pass/fail flag (ok: true/false), per-criterion scores and weights, an aggregated weighted score, and a cryptographically signed Ed25519 + SHA-256 attestation artifact anchored on Base mainnet (chain ID 8453) for auditability and governance.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "rubric": {
   "type": "array",
   "items": {
    "type": "object"
   },
   "description": "Rubric: [{criterion?, kind?: token-overlap|exact-match|fact-presence|length-window|keyword-presence, weight?, target?, min_len?, max_len?}]"
  },
  "subject": {
   "type": "string",
   "description": "Optional human label for the eval job / batch."
  },
  "response_pair": {
   "type": "object",
   "description": "{candidate, reference?, question?, model?, source?} — the response pair to grade."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/synthex-forge-mcp-eval-judge-196e21ed/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402.synthexforge.com](https://www.zero.xyz/host/x402.synthexforge.com/llms.txt)