Foldr.Space
x402 - HTTP 402 Payment Required, revived

5¢ per upload. USDC on Base.
No subscription.

Foldr.Space is the file backend for autonomous agents. Pay per upload, with no credit card, no signup tax, no monthly minimum - just a Base wallet and 5¢ in USDC.

Get an API keySee the upload tutorial

Why x402 over a subscription?

Agents already hold wallets

Autonomous agents don't fill out billing forms. They sign transactions. x402 slots straight into the existing wallet they use for everything else on-chain.

Pay only when you upload

No monthly fee, no committed quota. An agent that does ten uploads pays 50¢; an agent that does ten thousand pays $500. Linear, predictable, no surprise overages.

Settled on-chain, idempotent

Every payment leaves a tx hash you can audit. Retries with the same Idempotency-Key never double-charge.

How a paid upload looks

1

Agent posts the file

POST /api/v1/files
Authorization: Bearer fs_…
Content-Type: multipart/form-data

(file=@report.pdf)
2

Foldr returns 402 with x402 requirements

HTTP/1.1 402 Payment Required

{
  "x402Version": 1,
  "accepts": [{
    "scheme": "exact",
    "network": "base",
    "maxAmountRequired": "50000",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "payTo": "0x0fF790fBBF1D26E533cCaf9c9C01EBE728509f74",
    "resource": "https://foldr.space/api/v1/files",
    "description": "5¢ per upload",
    "maxTimeoutSeconds": 60
  }]
}
3

Agent signs and retries

POST /api/v1/files
Authorization: Bearer fs_…
X-PAYMENT: <base64 of signed payment payload>
Idempotency-Key: ulid-xyz…

(file=@report.pdf)

The signed payload is an EIP-3009 transferWithAuthorization for 0.05 USDC, verified by Coinbase's x402 facilitator and settled on-chain after the upload succeeds.

Foldr returns 201 with the file

HTTP/1.1 201 Created

{
  "success": true,
  "file": {
    "id": "f5c…",
    "downloadUrl": "https://foldr.space/api/v1/files/f5c…",
    "publicUrl": "https://foldr.space/f/abc…",
    "size": 184223,
    "isPermanent": true
  }
}

Pricing

Pay-per-upload

5¢ / upload

Settled in USDC on Base via x402.

  • Permanent storage included
  • Idempotent writes - same key never charges twice
  • No subscription, no minimums, no overage cliffs
  • Tx hash on every payment - full audit trail
Pro tier

$25 / month

For high-volume agents - bypass per-call charges.

  • 100 GB storage included
  • 1M requests / month
  • Up to 100 MB per file (5 GB on Enterprise)
  • No per-upload charge

What you actually get

Idempotency-Key

Stripe-style retry safety on every write endpoint. Same key + same body replays the response - no double-charge.

Capability tokens

Time-bounded, use-capped, revocable share links. Hand a capability to a downstream model without giving up the API key.

Per-key folders

agent_folders scoped to your API key. Hierarchical, with denormalized counts.

Webhooks

file.uploaded, file.deleted, capability.minted with HMAC-signed deliveries and retry backoff.

MCP server

Streamable-HTTP at /api/mcp. 20+ tools - Claude Desktop / Cursor / Windsurf compatible.

OpenAPI 3.1

Full spec at /openapi.json. Codegen-friendly, agent-discoverable.

FAQ

What is x402?▾

An open HTTP payment protocol that revives the 402 Payment Required status. Servers describe the payment they want; clients sign a stablecoin transfer payload and retry with the X-PAYMENT header. Verified + settled by a facilitator (we use Coinbase’s).

How much does an upload cost?▾

5¢ USDC per upload. Pro tier API keys at $25/mo bypass per-call charges entirely.

Which network and asset?▾

Base mainnet, USDC contract 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913.

Do I still need an API key?▾

Yes. The API key identifies which agent owns the resulting file (so list/move/delete work). x402 handles payment, the API key handles identity - separate concerns.

Are payments idempotent?▾

Yes. Send the same Idempotency-Key on retry and the original response replays without re-charging. The x402_payments ledger is keyed on (api_key_id, idempotency_key).

What if my agent doesn’t support x402 yet?▾

Top up account credits via /api/v1/agent/account/top-up and uploads debit from your balance instead. Same 5¢ per upload, same endpoints, no wallet required.

Build on Foldr.Space

Get an API key in seconds, point your agent's wallet at our 402 endpoint, and start uploading. Free for Pro+, 5¢ per upload otherwise.

Get an API keyView OpenAPI spec