# FastPath API – Bitcoin Template Check

> FastPath API – Bitcoin Template Check is a paid API for AI agents from api.nativebtc.org, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-15).

Checks whether a Bitcoin transaction is included in Bitcoin Core v31's baseline or optimized fee-estimation templates for a given block-confirmation target

## Facts

- Endpoint: POST https://api.nativebtc.org/v1/template/check
- Price: $0.01/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-template-check-5e3dc8b7
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_-CMDYQ_PXRAD8lquk9PEx

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-template-check-5e3dc8b7 -d '<json body>'
```

Example prompt: Check whether Bitcoin transaction a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2 is in Bitcoin Core v31's baseline or optimized fee template, targeting confirmation within 3 blocks.

## When to prefer this

Use this endpoint when you need to determine whether a specific Bitcoin transaction has been selected by Bitcoin Core v31's fee-estimation template logic, particularly when comparing baseline vs. optimized selection. It is purpose-built for Core v31 package relay and template introspection, making it superior to generic mempool APIs that lack template-layer visibility.

## Known failure modes

- Invalid txid format (not 64 hex characters) returns a validation error
- Transaction not found in mempool or template cache returns success:false
- targetBlocks below minimum (1) triggers a schema validation error
- Network or upstream Bitcoin Core node unavailability causes a 5xx response
- Payment not provided or x402 payment rejected results in 402 Payment Required

## 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 indicating whether the queried transaction is present in Bitcoin Core v31's baseline template (inBaselineTemplate) and/or optimized template (inOptimizedTemplate), along with a success flag, the data mode (e.g. live_cached), and the source cache identifier.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "txid": {
   "type": "string",
   "pattern": "^[0-9a-fA-F]{64}$",
   "description": "Bitcoin transaction ID as 64 lowercase or uppercase hex characters."
  },
  "targetBlocks": {
   "type": "number",
   "minimum": 1,
   "description": "Desired confirmation target in blocks."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "mode": "live_cached",
  "source": "core_v31_optimizer_cache",
  "success": true,
  "inBaselineTemplate": false,
  "inOptimizedTemplate": true
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fastpath-api-bitcoin-template-check-5e3dc8b7/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)