# Bitcoin Transaction Fee Rates & Cost Estimator

> Bitcoin Transaction Fee Rates & Cost Estimator is a paid API for AI agents from chain.openverbs.com, paid per call via x402, $0.006/call, status unknown (last checked 2026-09-15).

Returns live recommended Bitcoin fee rates (sat/vB) for five confirmation-speed tiers and estimates total fee cost for a transaction of a given virtual size.

## Facts

- Endpoint: POST https://chain.openverbs.com/v1/btc-fees
- Price: $0.006/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/bitcoin-transaction-fee-rates-cost-estimator-9da70f57
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_utkTWbJHLl1TNH6Xxa5Kb

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-transaction-fee-rates-cost-estimator-9da70f57 -d '<json body>'
```

Example prompt: What are the current Bitcoin fee rates for each confirmation speed, and how much would a 250 vbyte transaction cost in sats and BTC if I go with the next-block tier?

## When to prefer this

Use this endpoint when an agent needs to make fee-tier decisions before constructing or broadcasting a Bitcoin transaction, or when a user wants to know the real-time cost of sending Bitcoin at different confirmation speeds. It is purpose-built for Bitcoin fee estimation with per-tier breakdown and cost calculation in a single call, making it preferable to generic blockchain explorers that may not provide multi-tier fee estimates or cost projections.

## Known failure modes

- txvBytes out of range (below 1 or above 1,000,000) returns a validation error
- Mempool data temporarily unavailable returns a 503 or error response
- Malformed request body returns a 400 bad request
- Network timeout if mempool source is slow to respond

## How this service works

Live recommended Bitcoin transaction fee rates (in sat/vB) for next-block, ~30-minute, ~1-hour, economy and minimum confirmation targets, straight from the mempool. Also estimates the total fee (in sats and BTC) for a transaction of the given virtual size, so an agent can pick a fee tier and know the cost before broadcasting.

## Output

A structured response containing recommended fee rates in sat/vB for five tiers (next-block, ~30-minute, ~1-hour, economy, minimum), plus the estimated total fee in satoshis and BTC for a transaction of the requested virtual size at each tier, sourced live from the Bitcoin mempool.

## 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",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "properties": {
      "txvBytes": {
       "type": "integer",
       "default": 140,
       "maximum": 1000000,
       "minimum": 1,
       "description": "Virtual size of the transaction in vbytes, used to estimate the total fee at each tier. Defaults to 140 (a typical 1-in/2-out native-segwit spend)."
      }
     },
     "additionalProperties": false
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/bitcoin-transaction-fee-rates-cost-estimator-9da70f57/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from chain.openverbs.com](https://www.zero.xyz/host/chain.openverbs.com/llms.txt)