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bitcoin-fees-advisor

bitcoin-fees-advisor is a REST + SSE API for Bitcoin fee estimation, updated every 10-30 seconds. It aggregates data from multiple sources and provides a complete fee management toolkit for production wallets, exchanges, and payment processors.

Use it when you need to:

  • Display accurate sat/vB fee tiers to users before transaction signing
  • Calculate RBF bump amounts for stuck transactions (BIP125)
  • Plan CPFP child transactions to accelerate a stuck parent
  • Target a specific confirmation window (confirm within N seconds at probability P)
  • Optimize a batch of transactions for minimum total cost
  • Monitor mempool conditions in real time via SSE

Endpoints​

Fee recommendations​

GET /fees - Current fee tiers

Returns fast / medium / slow sat/vB values.

# Basic fee tiers
curl https://api.overblock.io/bitcoin-fees/fees \
  -H "X-API-Key: your-token"

# With txType: adds estimatedVsize and estimatedFeeSat
curl "https://api.overblock.io/bitcoin-fees/fees?txType=p2wpkh" \
  -H "X-API-Key: your-token"

Supported txType values: p2pkh, p2sh-p2wpkh, p2wpkh, p2tr, p2wsh-2of3.

GET /fee-advisor/market - Full mempool state

Returns mempool tx count, total vbytes, fee histogram, thresholds for 1/3/6 blocks, miner bias, and avg block interval.

Advanced fee tools​

POST /fee-advisor/rbf-bump - RBF replacement fee calculator

Given a stuck transaction, returns the minimum fee rate required to replace it per BIP125.

curl -X POST https://api.overblock.io/bitcoin-fees/fee-advisor/rbf-bump \
  -H "X-API-Key: your-token" \
  -H "Content-Type: application/json" \
  -d '{
    "currentFeeRateSatVb": 20,
    "currentFeeSat": 2820,
    "vsize": 141,
    "targetBlocks": 1
  }'

POST /fee-advisor/deadline - Deadline-based fee

Returns the fee rate needed to confirm a transaction within deadlineSec seconds at targetProbability.

POST /fee-advisor/cpfp - CPFP child fee planner

Given a stuck parent transaction, calculates the required fee for a child transaction to accelerate confirmation via CPFP.

POST /fee-advisor/batch - Batch transaction planner

Optimally distributes N transactions across time to minimize total fee cost, given a deadline.

Strategies: minimize_cost (wave scheduling), uniform (even distribution), asap (all immediately).

Transaction monitoring​

GET /tx-status?txids=abc,def - Transaction status

Returns status for each txid: in_mempool, confirmed, replaced_by_rbf, or unknown.

Note: only tracks transactions observed since the crawler started. Historical lookups are not supported.

GET /address-seen?addresses=addr1 - Address activity

Returns whether an address has been seen in the mempool or confirmed blocks since startup.

Real-time streaming (SSE)​

GET /fees/stream - Fee update stream

Server-Sent Events stream. Emits fees events (fast/medium/slow) and mempool events (tx count, vbytes). Throttled to at most one update per 30 seconds. Heartbeat every 25 seconds.

GET /events/stream?txids=abc&addresses=addr1 - Transaction watch stream

Emits events for specific txids and addresses: tx.seen, tx.confirmed, tx.replaced, address.activity.

Update interval​

Fee recommendations are refreshed every 10-30 seconds based on mempool activity. During high congestion, updates are more frequent.

Billing​

  • Free - rate-limited requests per minute
  • PAYG / requests - per API call, micro-USD per request
  • Subscription / credits - monthly request credits pool

Next steps​

Related reading: Bitcoin Fee Estimation for Developers · Integrating Fee Estimation into a Wallet