# WebCrypt MCP Server

Adds cryptographic primitives directly to AI coding agents via Web Crypto API. It runs with zero runtime dependencies on Node.js 18 or newer.

- MCP server · `type=mcp` · Claude Code, Codex, Cursor, GitHub Copilot, Windsurf (Devin Desktop), Cline, Zed, Gemini CLI · ★ 11
- Author: putervision
- License: MIT · policy=link-only · description only; the file stays with the author
- Source: https://github.com/putervision/WebCrypt
- Updated: 2026-08-21
- HTML: https://affpapa.org/en/nevibecode/mcp/webcrypt-mcp-server

## What it does

This server gives coding agents a local security toolkit. It handles symmetric AES-256-GCM encryption, RSA-4096 hybrid public keys, and SHA hashing digests. It also includes post-quantum algorithms such as Kyber and Dilithium. Agents can encrypt tokens before saving them to disk.

Six tools handle cryptographic workflows: `encrypt_payload`, `decrypt_payload`, `manage_keys`, `crypto_hash`, `sign_verify`, and `pqc_kem_sign`. Everything relies on the native `crypto.subtle` engine. No extra packages are needed.

The server expects Node.js 18 or higher. Without runtime Web Crypto support, calls fail immediately.

## Requirements
- Needs: Node.js (commands run via npx)

## Install

### Claude Code (native platform)

**Platform CLI**
```bash
claude mcp add webcrypt -- npx -y webcrypt
```

### Codex

**Platform CLI**
```bash
codex mcp add webcrypt-mcp-server -- npx -y webcrypt
```

### Cursor

**Config file**
File `.cursor/mcp.json`:
```json
{
    "mcpServers": {
        "webcrypt-mcp-server": {
            "command": "npx",
            "args": [
                "-y",
                "webcrypt"
            ]
        }
    }
}
```

### GitHub Copilot

**Config file**
File `.vscode/mcp.json`:
```json
{
    "servers": {
        "webcrypt-mcp-server": {
            "type": "stdio",
            "command": "npx",
            "args": [
                "-y",
                "webcrypt"
            ]
        }
    }
}
```

### Gemini CLI

**Platform CLI**
```bash
gemini mcp add webcrypt-mcp-server npx -y webcrypt
```

## When to use it
- encrypt agent secrets before writing files to disk
- sign code diffs and release builds with digital signatures
- generate ephemeral JWK keypairs for agent communication
- calculate cryptographic hashes using SHA-256 or SHA-512

## Example prompts
- Generate a fresh RSA-4096 keypair using `manage_keys` and display the public key
- Encrypt the `.env` contents using `encrypt_payload` with symmetric AES-256-GCM
- Verify the release bundle hash with `sign_verify`

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