# ReqBin MCP

> ReqBin sends JSON payloads to an echo service and returns that exact data structure, letting you inspect how APIs receive your data. Use it to validate request formats, confirm data types (like prices or IDs), and debug complex API schemas before writing a line of code.

## Overview
- **Category:** developer-tools
- **Price:** Free
- **Tags:** api-testing, json-echo, debugging, request-validation, http-client

## Description

You know how bad API requests can be? You spend hours building an agent that looks perfect on paper, only for it to fail because a field name was misspelled or a number got treated like text. This server fixes that. It lets your AI client send data and see exactly what the receiving end gets back.

The whole point here is debugging. We're talking about inspecting raw JSON payloads in real-time. The core function you use is `echo_post_json`. When you run `echo_post_json`, you're sending a structured JSON payload to ReqBin, and the server immediately sends back that exact structure. That return data is what you analyze to make sure your agent’s output matches the API schema it needs to talk to.

**Echo Data Payloads:** You can send any custom JSON object—whether it's an ID number, a price point, or some complex nested array—and you get that identical structure back. This lets you verify the data payload *before* you commit your agent to making a real call. If you need to confirm how a specific system handles coordinates (latitude/longitude) or if a unique product SKU is being sent as a string versus an integer, this tool shows it right up front.

**Verify Schema Structure:** This capability lets you check the scaffolding of your JSON object. You're confirming that when your AI agent builds a payload for a specific endpoint—say, one that requires `user_id` nested under a root key called `customer_data`—that structure is correct. If it’s missing a closing bracket or if you accidentally swapped the order of keys, the echo response tells you immediately where the schema breaks down. You'll know if your agent is building objects with the required field names and nesting for that specific API.

**Test Data Types:** It’s critical to confirm data types are respected. When you run this through `echo_post_json`, it verifies whether numbers remain numeric, if boolean values (true/false) pass through correctly, or if strings stay exactly as they should. If the receiving system expects a float for pricing but your agent sends it with unnecessary quotes, the echo response will show that mismatch so you can adjust your prompt.

**Validate Connectivity:** You don't even need to send data to run a quick sanity check. The tool runs a default test right out of the gate, confirming that your AI client can connect and communicate with the entire echo service endpoint immediately. It’s a fast way to rule out connection issues or authentication failures before you get deep into complex payload testing.

Basically, if your agent is talking to an API, you need this server. You use `echo_post_json` to send the data, and that exact JSON structure comes back. Then you analyze it to confirm everything—the field names, the nesting, the data types—is locked down tight before writing a single line of production code.

## Tools

### echo_post_json
Sends a JSON payload to ReqBin and returns that exact data structure in the response for immediate inspection.

## Prompt Examples

**Prompt:** 
```
Send a test JSON payload to ReqBin with Id 123 and Price 50.00.
```

**Response:** 
```
I've sent the payload to ReqBin Echo. The server responded with the echoed data: Id 123 and Price 50.00. This confirms the request structure was sent correctly.
```

**Prompt:** 
```
Verify my request structure by echoing a JSON object with Quantity 5.
```

**Response:** 
```
Request sent. ReqBin Echo returned the following JSON: { "Quantity": 5 }. Your agent is correctly formatting the quantity field.
```

**Prompt:** 
```
Run a default ReqBin echo test to check connectivity.
```

**Response:** 
```
Connectivity test successful. I sent a default payload and ReqBin Echo successfully returned Id 78912, Quantity 1, and Price 18.00.
```

## Capabilities

### Echo Data Payloads
Send any custom JSON object—containing fields like IDs or prices—and receive that identical structure back.

### Verify Schema Structure
Check if your AI agent is building JSON objects with the correct field names and nesting for a specific API.

### Test Data Types
Confirm that numbers are treated as numbers, strings remain strings, and boolean values pass through correctly.

### Validate Connectivity
Run a default test to confirm your AI client can communicate with the echo service endpoint immediately.

## Use Cases

### Building a Payment Gateway Client
The developer needs to send transaction data. They run `echo_post_json` with sample fields: { "user_id": 500, "amount": 99.99, "currency": "USD"}. The echo response confirms the amount is a float and the currency is a string, validating the payment payload structure before integrating it with Stripe.

### QA Checking Order Forms
The QA engineer must confirm that all required fields for an order are present. They use `echo_post_json` multiple times, deliberately leaving out a field like 'shipping_address'. The echo response fails to include the expected key, signaling a schema bug in the front-end form logic.

### Integrating Microservices
An integrator needs Service A's output to match Service B's input. They run `echo_post_json` simulating Service A’s response. By inspecting the echoed data, they find that 'user_name' is capitalized in the output but must be lowercase for Service B.

### Debugging Agent Output
The agent fails when calling an external API because it formatted dates wrong. The user runs `echo_post_json` with various date formats until the echoed response shows the required ISO 8601 structure, fixing the data formatting issue in the prompt.

## Benefits

- Confirm data types instantly. When you run `echo_post_json`, the server confirms if your fields—like quantities or prices—are being treated as numbers or strings, saving tricky type-mismatch bugs later.
- Validate complex schemas quickly. Need to ensure a payload has an ID, a status code, and multiple items? Send it via `echo_post_json` and inspect the response to guarantee every field is present.
- Bypass mock server setup. You don't need to build or manage local mock endpoints. Just call `echo_post_json` and get real-time feedback on your structure, right inside your chat agent.
- Test edge cases easily. Want to see what happens if you omit a field? Send a partial payload using the tool. The echo response immediately highlights which required parts are missing or malformed.
- Verify connectivity fast. Use the default test function in `echo_post_json` to confirm your client is talking to ReqBin without needing any setup keys or environment variables.

## How It Works

The bottom line is: you get immediate feedback on your request's structure without needing to set up any mock servers or complex local environments.

1. Initiate the connection by calling `echo_post_json` and providing the JSON data you want to test.
2. The ReqBin server processes the input and returns an echo response that mirrors your submitted payload.
3. Review the returned JSON structure. This output confirms whether the field names, data types, and format are ready for a production API call.

## Frequently Asked Questions

**Can I send custom fields like Price and Quantity to the echo service?**
Yes! Use the `echo_post_json` tool. You can optionally provide an Id, Quantity, and Price. The server will send these to ReqBin and return the echoed JSON so you can verify the structure.

**What happens if I run the echo tool without any parameters?**
If no specific fields are provided, the `echo_post_json` tool sends a default payload (Id: 78912, Quantity: 1, Price: 18.00) to verify that the connection to ReqBin is working correctly.

**Is this tool intended for production data storage?**
No. This is a debugging and testing tool. It uses ReqBin's Echo API to reflect back the data you send, making it ideal for verifying that your AI agent is formatting JSON requests correctly.

**Does running `echo_post_json` require specific API keys or authentication?**
No, you don't need complex credentials. The public echo endpoint is designed to be accessible for basic testing without requiring special API keys. This keeps connectivity checks simple for developers.

**What happens if I send improperly formatted JSON when using `echo_post_json`?**
The server will reflect the error, allowing you to debug your payload structure immediately. Because it's an echo service, syntax errors are visible in the response data.

**Which AI clients support the `echo_post_json` tool?**
You can connect any MCP-compatible client to this server. This includes platforms like Claude, Cursor, VS Code, and Windsurf. Any agent that uses the Model Context Protocol will work here.

**Is there a rate limit if I run `echo_post_json` many times during heavy QA testing?**
The service is built for debugging, but like any hosted resource, usage limits apply. For large-scale automated testing, monitor your request volume to prevent hitting potential API quotas.

**When I use `echo_post_json`, can I guarantee the response structure matches my input?**
Yes. The tool functions as a direct echo utility. Its main purpose is reflecting your exact request payload, so the output data structure will match what you sent it.