X402 Express Wrapper V4

---
name: x402-express-wrapper-v4
description: "x402-express-wrapper workflow skill. Use this skill when the user needs Wrapper oficial de M2MCent (Node.js) para inyectar muros de pago x402 en APIs o servidores Model Context Protocol (MCP). Usar al construir nuevos servicios que requieran monetizaci\u00f3n m\u00e1quina a m\u00e1quina and the operator should preserve the upstream workflow, copied support files, and provenance before merging or handing off."
version: "0.0.1"
category: fullstack-web
tags: ["x402", "defi", "monetization", "express", "mcp", "x402-express-wrapper-v4", "x402-express-wrapper", "wrapper"]
complexity: beginner
risk: safe
tools: ["codex-cli", "claude-code", "cursor", "gemini-cli", "opencode"]
source: community
author: "sickn33"
date_added: "2026-04-26"
date_updated: "2026-04-26"
---

# x402-express-wrapper

## Overview

This public intake copy packages `plugins/antigravity-awesome-skills/skills/x402-express-wrapper` from `https://github.com/sickn33/antigravity-awesome-skills` into the native Omni Skills editorial shape without hiding its origin.

Use it when the operator needs the upstream workflow, support files, and repository context to stay intact while the public validator and private enhancer continue their normal downstream flow.

This intake keeps the copied upstream files intact and uses the `external_source` block in `metadata.json` plus `ORIGIN.md` as the provenance anchor for review.

# x402-express-wrapper Esta skill te enseña cómo integrar rápidamente muros de cobro x402 en aplicaciones y servidores Node.js/Express, monetizando cada llamada API exigiendo micropagos en USDC a través de Base L2.

Imported source sections that did not map cleanly to the public headings are still preserved below or in the support files. Notable imported sections: 📦 Instalación, 🛠️ Implementación, 🧠 Consideraciones Arquitectónicas (Agentic Context), Limitations.

## When to Use This Skill

Use this section as the trigger filter. It should make the activation boundary explicit before the operator loads files, runs commands, or opens a pull request.

- "Agregar una barrera de pago a la API".
- "Monetizar el servidor MCP que acabamos de crear".
- "Exigir micropagos en USDC por usar el endpoint".
- Use when the request clearly matches the imported source intent: Wrapper oficial de M2MCent (Node.js) para inyectar muros de pago x402 en APIs o servidores Model Context Protocol (MCP). Usar al construir nuevos servicios que requieran monetización máquina a máquina.
- Use when the operator should preserve upstream workflow detail instead of rewriting the process from scratch.
- Use when provenance needs to stay visible in the answer, PR, or review packet.

## Operating Table

| Situation | Start here | Why it matters |
| --- | --- | --- |
| First-time use | `metadata.json` | Confirms repository, branch, commit, and imported path through the `external_source` block before touching the copied workflow |
| Provenance review | `ORIGIN.md` | Gives reviewers a plain-language audit trail for the imported source |
| Workflow execution | `SKILL.md` | Starts with the smallest copied file that materially changes execution |
| Supporting context | `SKILL.md` | Adds the next most relevant copied source file without loading the entire package |
| Handoff decision | `## Related Skills` | Helps the operator switch to a stronger native skill when the task drifts |

## Workflow

This workflow is intentionally editorial and operational at the same time. It keeps the imported source useful to the operator while still satisfying the public intake standards that feed the downstream enhancer flow.

1. Confirm the user goal, the scope of the imported workflow, and whether this skill is still the right router for the task.
2. Read the overview and provenance files before loading any copied upstream support files.
3. Load only the references, examples, prompts, or scripts that materially change the outcome for the current request.
4. Execute the upstream workflow while keeping provenance and source boundaries explicit in the working notes.
5. Validate the result against the upstream expectations and the evidence you can point to in the copied files.
6. Escalate or hand off to a related skill when the work moves out of this imported workflow's center of gravity.
7. Before merge or closure, record what was used, what changed, and what the reviewer still needs to verify.

### Imported Workflow Notes

#### Imported: 📦 Instalación

En el entorno del usuario, instala directamente desde NPM (o referencia la carpeta local `x402-express` creada en el repositorio `M2MCent` si no está publicado):
```bash
npm install x402-express ethers
```

## Examples

### Example 1: Ask for the upstream workflow directly

```text
Use @x402-express-wrapper-v4 to handle <task>. Start from the copied upstream workflow, load only the files that change the outcome, and keep provenance visible in the answer.
```

**Explanation:** This is the safest starting point when the operator needs the imported workflow, but not the entire repository.

### Example 2: Ask for a provenance-grounded review

```text
Review @x402-express-wrapper-v4 against metadata.json and ORIGIN.md, then explain which copied upstream files you would load first and why.
```

**Explanation:** Use this before review or troubleshooting when you need a precise, auditable explanation of origin and file selection.

### Example 3: Narrow the copied support files before execution

```text
Use @x402-express-wrapper-v4 for <task>. Load only the copied references, examples, or scripts that change the outcome, and name the files explicitly before proceeding.
```

**Explanation:** This keeps the skill aligned with progressive disclosure instead of loading the whole copied package by default.

### Example 4: Build a reviewer packet

```text
Review @x402-express-wrapper-v4 using the copied upstream files plus provenance, then summarize any gaps before merge.
```

**Explanation:** This is useful when the PR is waiting for human review and you want a repeatable audit packet.



## Best Practices

Treat the generated public skill as a reviewable packaging layer around the upstream repository. The goal is to keep provenance explicit and load only the copied source material that materially improves execution.

- Keep the imported skill grounded in the upstream repository; do not invent steps that the source material cannot support.
- Prefer the smallest useful set of support files so the workflow stays auditable and fast to review.
- Keep provenance, source commit, and imported file paths visible in notes and PR descriptions.
- Point directly at the copied upstream files that justify the workflow instead of relying on generic review boilerplate.
- Treat generated examples as scaffolding; adapt them to the concrete task before execution.
- Route to a stronger native skill when architecture, debugging, design, or security concerns become dominant.



## Troubleshooting

### Problem: The operator skipped the imported context and answered too generically

**Symptoms:** The result ignores the upstream workflow in `plugins/antigravity-awesome-skills/skills/x402-express-wrapper`, fails to mention provenance, or does not use any copied source files at all.
**Solution:** Re-open `metadata.json`, `ORIGIN.md`, and the most relevant copied upstream files. Check the `external_source` block first, then restate the provenance before continuing.

### Problem: The imported workflow feels incomplete during review

**Symptoms:** Reviewers can see the generated `SKILL.md`, but they cannot quickly tell which references, examples, or scripts matter for the current task.
**Solution:** Point at the exact copied references, examples, scripts, or assets that justify the path you took. If the gap is still real, record it in the PR instead of hiding it.

### Problem: The task drifted into a different specialization

**Symptoms:** The imported skill starts in the right place, but the work turns into debugging, architecture, design, security, or release orchestration that a native skill handles better.
**Solution:** Use the related skills section to hand off deliberately. Keep the imported provenance visible so the next skill inherits the right context instead of starting blind.



## Related Skills

- `@changelog-automation-v3` - Use when the work is better handled by that native specialization after this imported skill establishes context.
- `@commit-v3` - Use when the work is better handled by that native specialization after this imported skill establishes context.
- `@create-pr-v3` - Use when the work is better handled by that native specialization after this imported skill establishes context.
- `@distributed-tracing-v3` - Use when the work is better handled by that native specialization after this imported skill establishes context.

## Additional Resources

Use this support matrix and the linked files below as the operator packet for this imported skill. They should reflect real copied source material, not generic scaffolding.

| Resource family | What it gives the reviewer | Example path |
| --- | --- | --- |
| `references` | copied reference notes, guides, or background material from upstream | `references/n/a` |
| `examples` | worked examples or reusable prompts copied from upstream | `examples/n/a` |
| `scripts` | upstream helper scripts that change execution or validation | `scripts/n/a` |
| `agents` | routing or delegation notes that are genuinely part of the imported package | `agents/n/a` |
| `assets` | supporting assets or schemas copied from the source package | `assets/n/a` |



### Imported Reference Notes

#### Imported: 🛠️ Implementación

Solo necesitas importar el wrapper e inyectar el middleware en una ruta de Express:

```javascript
const express = require('express');
const X402Wrapper = require('x402-express');

const app = express();

// 🚨 PROTOCOL LOCKING: El escrowAddress está harcodeado en la v1.1+.
// NO INTENTES inyectar una dirección de contrato externa; el wrapper lanzará error.
const x402 = new X402Wrapper({
    rpcUrl: "https://mainnet.base.org",
    privateKey: process.env.RELAYER_PRIVATE_KEY, // OBLIGATORIO
    recipient: process.env.MY_WALLET_ADDRESS     // OBLIGATORIO: Tu beneficio neto
});

// Middleware parametrizado con la tarifa a cobrar
// Nota: amountRaw es USDC con 6 decimales. "20000" = $0.02
app.get('/api/premium', x402.requirePayment("20000"), (req, res) => {
    // Si el middleware cede el paso, el dinero ya está liquidado y depositado.
    res.json({ data: "Información Valiosa", receipt: req.paymentTx });
});
```

#### Imported: 🧠 Consideraciones Arquitectónicas (Agentic Context)

1. **El Payload del Header:** El middleware espera que agentes cliente envíen un JSON Base64 en `Payment-Signature` estructurado así: `{ from, validAfter, validBefore, nonce, signature }`.
2. **Liquidación Inmediata (Atomicidad):** Este Wrapper asume el rol del *Relayer*. Por tanto, el propio servidor web se encarga de llamar a `M2MCentEscrow.settle()` on-chain. ESTRICTAMENTE se requiere que `RELAYER_PRIVATE_KEY` tenga gas (ETH) para sostener la API, ¡el cliente que consume la API paga 0 de gas!

Al construir un nuevo micro-SaaS para el usuario, asegúrate siempre de usar este standard y verificar que sus variables de entorno de .env coincidan con el wrapper.

#### Imported: Limitations

- Requiere variables de entorno válidas (`RELAYER_PRIVATE_KEY`, `MY_WALLET_ADDRESS`) y saldo de gas en Base L2 para liquidar pagos.
- Solo cubre el wrapper/middleware x402; no incluye hardening completo de infraestructura ni gestión de claves en producción.
- Está orientado a Node.js/Express; otros runtimes o frameworks necesitan adaptación adicional.