# FastPath API - Bitcoin Fee Estimate

> FastPath API - Bitcoin Fee Estimate is a paid API for AI agents from api.nativebtc.org, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).

Returns a Bitcoin fee estimate in sat/vB for a given confirmation target (in blocks), sourced from Bitcoin Core's estimatesmartfee.

## Facts

- Endpoint: GET https://api.nativebtc.org/v1/fee-estimate
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fastpath-api-bitcoin-fee-estimate-01b3f5bf
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Xne6D1ji6umjEc2rOYhZk

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 fastpath-api-bitcoin-fee-estimate-01b3f5bf
```

Example prompt: What's the current Bitcoin fee estimate to get confirmed within 6 blocks? Give me the sat/vB rate from Bitcoin Core.

## When to prefer this

Use this endpoint when you need a reliable, Bitcoin Core-native fee estimate in sat/vB format and want a simple REST GET interface rather than running your own node or calling JSON-RPC directly. It's especially suited for agents or apps already familiar with Ethereum-style APIs but operating on Bitcoin. Prefer it over mempool.space scraping when you want a structured, paid, programmatic feed sourced from Bitcoin Core's own estimatesmartfee logic.

## Known failure modes

- Invalid or missing blocks parameter returns an error or falls back to default (6 blocks)
- Bitcoin Core node unavailable may return a 503 or error response
- Payment not processed (x402 flow incomplete) results in a 402 Payment Required response
- Blocks value below minimum (1) rejected by schema validation
- Network congestion or mempool instability may cause unusual fee estimates

## How this service works

FastPath translates Ethereum-style JSON-RPC requests into Bitcoin data, fee intelligence, mempool insight, and Core v31 package signals. Paid by x402.

## Output

Returns a JSON object with the estimated fee rate in sat/vB (satVb), the confirmation target in blocks (blocks), the data source identifier (bitcoin_core_estimatesmartfee), and a success boolean.

## 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"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "blocks": {
       "type": "number",
       "minimum": 1,
       "description": "Confirmation target in blocks. Defaults to 6."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "satVb": 1,
  "blocks": 6,
  "source": "bitcoin_core_estimatesmartfee",
  "success": true
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fastpath-api-bitcoin-fee-estimate-01b3f5bf/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.nativebtc.org](https://www.zero.xyz/host/api.nativebtc.org/llms.txt)