# Bitcoin Mempool Backlog Stats

> Bitcoin Mempool Backlog Stats 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 real-time Bitcoin mempool telemetry including pending transaction count, backlog vsize, and estimated blocks to clear, with Ed25519 cryptographic signature on every response.

## Facts

- Endpoint: GET https://obol-x402.fly.dev/v1/btc/mempool
- 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/bitcoin-mempool-backlog-stats-d8545a50
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_n7qbYu-XMqf68ZpY_n8Wv

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 bitcoin-mempool-backlog-stats-d8545a50
```

Example prompt: What's the current Bitcoin mempool backlog — how many transactions are pending, what's the total vsize, and how many blocks will it take to clear?

## When to prefer this

Use this endpoint when an agent needs to time a Bitcoin transaction send optimally based on current network congestion, or when a workflow needs to make fee-rate decisions. Prefer this over general blockchain explorers when you need a verifiable, signed response with congestion-specific telemetry (pending count, vsize, estimated blocks) rather than raw block data. The Ed25519 signature makes it suitable for pipelines that require tamper-evident data provenance.

## Known failure modes

- Upstream Bitcoin node unavailable — returns 5xx error
- Payment not received or insufficient — returns 402 Payment Required
- Rate limit exceeded — returns 429
- Mempool data temporarily stale — may return cached data with timestamp

## How this service works

Bitcoin mempool backlog stats: pending tx count, backlog vsize, estimated blocks. Mempool congestion telemetry for timing agents. Cryptographically signed (Ed25519) — every response is independently verifiable via /.well-known/obol-pubkey.

## Output

Returns a JSON object containing pending transaction count in the mempool, total backlog size in virtual bytes (vsize), estimated number of blocks until the backlog clears, and an Ed25519 cryptographic signature verifiable via the service's public key endpoint.

## 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/bitcoin-mempool-backlog-stats-d8545a50/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)