# Obol BTC Next-Block Fee Estimator

> Obol BTC Next-Block Fee Estimator is a paid API for AI agents from obol-x402.fly.dev, paid per call via x402, $0.01/call, status down (last checked 2026-09-15).

Returns a single Bitcoin next-block fee estimate in sat/vB for the fastest transaction confirmation

## Facts

- Endpoint: GET https://obol-x402.fly.dev/v1/btc/fee/next-block
- Price: $0.01/call
- Payment: x402
- Status: down
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/obol-btc-next-block-fee-estimator-ce85707d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_HmpTrdx-TFtFj6ja45nAH

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability obol-btc-next-block-fee-estimator-ce85707d
```

Example prompt: What's the current Bitcoin next-block fee in sat/vB? I need the fastest confirmation fee estimate so I can build my BTC transaction right now.

## When to prefer this

Choose this endpoint when you need the single fastest, simplest Bitcoin next-block fee estimate with minimal overhead. It is ideal for agents building BTC transactions that require urgent confirmation and need just one actionable sat/vB number without additional mempool context or congestion analysis. If you also need mempool congestion tier, broadcast advice, or multi-asset price data, consider the sibling bundle endpoint instead.

## Known failure modes

- Mempool data temporarily unavailable — service may return an error or stale estimate
- Network connectivity issues to the fly.dev backend may produce timeouts
- Payment failure (x402) if USDC balance is insufficient or payment not processed
- Rate limiting if too many calls are made in rapid succession

## How this service works

Returns the next-block Bitcoin fee estimate in sat/vB, along with an Ed25519 attestation for verification. Useful for fee-aware routing and transaction timing.

## Output

A single numeric fee rate in satoshis per virtual byte (sat/vB) representing the estimated cost to get a Bitcoin transaction confirmed in the very next block.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {}
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/obol-btc-next-block-fee-estimator-ce85707d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from obol-x402.fly.dev](https://www.zero.xyz/host/obol-x402.fly.dev/llms.txt)