@slidingbox/hydrate-dehydrate-mcp

An MCP server for handing a secret from one agent, machine, or person to another without leaving a copy behind.

store_secret encrypts on your machine and returns one token. Whoever holds the token gets the secret exactly once — the first successful read delivers it and destroys it, and a second read returns nothing. Slidingbox stores only ciphertext: the key travels in the token and is never sent to the server.

Code

store_secret("sk-live-...")  ->  sb_PApm-Ui...#0zgYgq2d...
                                 ^ pointer, on the server   ^ key, never sent

retrieve_secret("sb_PApm-Ui...#0zgYgq2d...")  ->  sk-live-...   (and it's gone)

Install

config.json

{
  "mcpServers": {
    "hydrate-dehydrate": {
      "command": "npx",
      "args": ["-y", "@slidingbox/hydrate-dehydrate-mcp"],
      "env": { "SLIDINGBOX_API_KEY": "sbk_..." }
    }
  }
}

That block goes in your MCP client's config — claude_desktop_config.json for Claude Desktop, or claude mcp add for Claude Code.

Paying for reads

Storing is free. Reading costs $0.02, and there are two ways to cover it:

Variable	What it does
`SLIDINGBOX_API_KEY`	An evaluation key (`sbk_<id>.<hmac>`). Covers a fixed number of reads for free. Get one instantly: `curl -X POST https://slidingbox.ai/v1/key` — no account, no email.
`SLIDINGBOX_PRIVATE_KEY`	A Base wallet holding USDC. Reads are paid per call over x402 — no account, no invoice, no subscription.
`SLIDINGBOX_URL`	Defaults to `https://slidingbox.ai`.
`SLIDINGBOX_NETWORK`	Defaults to `eip155:8453` (Base mainnet).

With neither set, store_secret still works and retrieve_secret tells you which one to configure. SLIDINGBOX_PRIVATE_KEY signs payments: give it a wallet funded for this purpose and nothing else.

What it is good for

Passing a credential between two agents that share no store and no account.
Sending a secret through a channel you would rather it not persist in — the token in the chat log is inert the moment it is read.
Proving a handoff happened once. A replayed token fails visibly instead of quietly serving a second copy.

What it is not

Not storage, backup, messaging, or key management. Secrets live 60–900 seconds and then expire. Not for protected health information or payment-card data.

How it works

Encryption is AES-256-GCM, done in this process before anything is sent. The server receives {ciphertext, iv} and a time-to-live, and returns an opaque pointer. That is the whole reason this is a local stdio server rather than a route on the API: a remote MCP server would have to receive your plaintext in order to encrypt it.

Payment, when a wallet is configured, is x402 — the read returns 402, the client signs an EIP-3009 authorization for $0.02 USDC, and retries. Paying wallets are screened against the OFAC SDN list before settlement; see https://slidingbox.ai/compliance.

API: https://slidingbox.ai/developers
Agent-readable: https://slidingbox.ai/llms.txt, https://slidingbox.ai/.well-known/slidingbox.json

Development

Terminal

npm install
npm test        # offline: crypto round-trip and token parsing
node server.mjs # speaks MCP over stdio

If this stops working

Slidingbox is a small product and may be retired. This server is built to say so rather than fail opaquely: a retired service answers 410, and a domain that no longer resolves is reported as a retirement, not as a stack trace. Nothing you store is ever held longer than 900 seconds, so a shutdown cannot strand data.