# PQS Compare - Head-to-Head Prompt Scoring Across Models

> PQS Compare - Head-to-Head Prompt Scoring Across Models is a paid API for AI agents from promptqualityscore.com, paid per call via x402, $1.25/call, status unknown (last checked 2026-09-13).

Scores a prompt against 8 quality dimensions, runs it through multiple LLMs (GPT-4o and Claude), compares outputs with scores, and returns an optimized prompt with a winner verdict.

## Facts

- Endpoint: GET https://promptqualityscore.com/api/score/compare
- Price: $1.25/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/pqs-compare-head-to-head-prompt-scoring-across-models-83e2f4b1
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap__ymt6Y6X6zB-T_hSMMnPG

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 pqs-compare-head-to-head-prompt-scoring-across-models-83e2f4b1
```

Example prompt: Run a PQS compare on this prompt against the software vertical and tell me which model wins and what the optimized version looks like: 'You are a senior engineer. Review the following code diff and list any bugs, performance issues, and security vulnerabilities in order of severity.'

## When to prefer this

Use this endpoint when you need to compare how multiple LLMs handle the same prompt side-by-side, get dimension-level quality scores, and receive an auto-optimized prompt rewrite — all in one call. Prefer this over the basic scoring endpoint when model selection matters or when you want a concrete recommendation on which model to use for a given prompt. Ideal for prompt QA pipelines before deploying to production, or when evaluating a new prompt for an AI agent.

## Known failure modes

- Empty or missing prompt field returns validation error
- Prompt exceeds 10,000 character limit
- Invalid vertical enum value causes rejection
- Payment not included or insufficient (x402 payment required at $1.25 USDC)
- LLM provider timeout causes incomplete comparison results
- Network error from upstream model providers

## How this service works

A Quality Gate For Prompts. Before they break production. Score any AI prompt against 8 dimensions, see what's weak, and get the fixed version in seconds.

## Output

Returns a JSON object with: the winning model name, per-model outputs and dimension scores (relevancy, completeness, faithfulness, reasoning_depth, total), a natural-language verdict explaining why one model outperformed the other, the original prompt, and an AI-optimized rewrite of the prompt. Also includes PQS version and the vertical used.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "prompt": {
   "type": "string",
   "maxLength": 10000,
   "minLength": 1,
   "description": "Prompt to score"
  },
  "vertical": {
   "enum": [
    "software",
    "content",
    "business",
    "education",
    "science",
    "crypto",
    "general",
    "research"
   ],
   "type": "string",
   "default": "general",
   "description": "Domain: software/content/business/education/science/crypto/general/research"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "winner": "claude",
  "results": {
   "gpt4o": {
    "model": "gpt-4o",
    "output": "PQS measures prompt quality across 8 dimensions before the prompt reaches the model - a pre-flight gate for AI-agent buyers.",
    "scores": {
     "total": 32,
     "relevancy": 9,
     "completeness": 8,
     "faithfulness": 8,
     "reasoning_depth": 7
    }
   },
   "claude": {
    "model": "claude-sonnet-4-6",
    "output": "PQS scores any LLM prompt on 8 dimensions pre-inference so x402 API buyers can reject low-quality inputs before paying.",
    "scores": {
     "total": 35,
     "relevancy": 9,
     "completeness": 9,
     "faithfulness": 9,
     "reasoning_depth": 8
    }
   }
  },
  "verdict": "Claude's response names the exact buyer action (reject) and ties to x402, giving the technical buyer a concrete decision rule.",
  "vertical": "general",
  "powered_by": "PQS - promptqualityscore.com",
  "pqs_version": "2.0",
  "original_prompt": "Explain PQS scoring in one sentence to an AI agent operator.",
  "optimized_prompt": "You are an AI-agent product manager. In one sentence (max 25 words), explain PQS scoring to a technical buyer evaluating x402 APIs."
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/pqs-compare-head-to-head-prompt-scoring-across-models-83e2f4b1/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from promptqualityscore.com](https://www.zero.xyz/host/promptqualityscore.com/llms.txt)