# Bitcoin Chain Tip Height

> Bitcoin Chain Tip Height 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 the current Bitcoin blockchain tip (latest block height), cryptographically signed with Ed25519 for independent verifiability.

## Facts

- Endpoint: GET https://obol-x402.fly.dev/v1/btc/tip
- 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-chain-tip-height-53fa56ea
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_u0ROB3qDHBDi-J0f-wkmL

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-chain-tip-height-53fa56ea
```

Example prompt: What's the current Bitcoin block height right now? I need the latest chain tip with a cryptographic signature so I can verify it independently.

## When to prefer this

Choose this endpoint when you need a lightweight, tamper-evident lookup of the current Bitcoin block height — especially when cryptographic verifiability of the response matters. Prefer over raw node RPC calls when you lack direct node access or need a signed attestation for downstream trust. Best for agents syncing height, triggering block-based workflows, or auditing chain progress.

## Known failure modes

- Service unavailable / 503 if fly.dev instance is down
- Payment required / 402 if x402 payment header is missing or invalid
- Stale tip if upstream Bitcoin node is temporarily unsynced
- Invalid signature if key rotation occurred and cached pubkey is outdated

## How this service works

Current Bitcoin chain tip height (latest block number) for agents syncing height. Cryptographically signed (Ed25519) — every response is independently verifiable via /.well-known/obol-pubkey.

## Output

Returns the current Bitcoin blockchain tip block height (latest block number), accompanied by an Ed25519 cryptographic signature that can be independently verified using the public key at /.well-known/obol-pubkey. Enables agents to confirm data authenticity without trusting the server.

## 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-chain-tip-height-53fa56ea/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)