Does the B2Pool API need a key?

No. Every endpoint under /api/v1/public is read-only and open, with no key, no registration and no CORS restriction. It is rate limited to 5 requests a second per address with a burst of 20, and answers 429 when you go past that.

Which URL should a pool tracker use?

https://b2pool.io/api/v1/public - one call that returns both pools with hashrate, fee, payout scheme, block counts and the chain's difficulty and subsidy. Clients that already speak Miningcore can use https://b2pool.io/api/pools instead, which returns the same pool list at the path they expect.

What is the block reward on BTCB2?

The subsidy is the same schedule as Bitcoin: 3.125 BTCB2 per block at present, halving every 210,000 blocks. On the shared pool only that subsidy is divided among miners; the transaction fees in the block stay with the pool. A profitability calculation should therefore use avgBlockReward, which is what miners were actually paid per block, rather than the whole coinbase.

Is BTCB2 mined with SHA-256?

No. BTCB2 is Bitcoin with BLAKE2b proof of work, the hardfork described in BIP-110, which took effect at block 961,640. The algorithm field in the API says blake2b for this reason. Hashrate for this chain is rented under Blake2B, sometimes still listed as Sia or SC.

One URL, everything.

A public read-only API for anyone listing, charting or comparing this pool. No key, no registration, no origin restriction. The shape is Miningcore's, because that is the one every pool scraper already has a parser for — if you have written a Miningcore adapter before, this needs nothing from you but the hostname.

https://b2pool.io/api/v1/public

JSON · cached 60 s · 5 req/s per address, burst 20 · answers 429 when you exceed it

If you are a tracker, this is the whole integration

One call, server-side, as often as once a minute. It returns both pools — shared and solo — with everything a listing or a profitability page needs.

Field	What it is
poolStats.poolHashrate	Pool hashrate in H/s.
networkStats.networkHashrate	Network hashrate, the same unit. The ratio of the two is the pool's true share — there is no scaling factor to apply between them.
networkStats.networkDifficulty	Network difficulty, same definition as the SHA-256 chain.
poolStats.connectedMiners	Distinct payout addresses currently mining. connectedWorkers counts machines.
poolFeePercent	1.0, on both pools.
blockReward	The nominal subsidy at the current height, in BTCB2.
avgBlockReward	What miners were actually paid, averaged over this pool's confirmed blocks — a block still maturing has not had its split booked yet, and averaging it in would overstate the figure. Use this one for profitability: see the note below, it is not the same as blockReward. Null until the pool has a confirmed block, which is why the solo pool reports null today.
blockTime	600 seconds. Same target as Bitcoin.
paymentProcessing	Scheme, minimum payout and what triggers a payout.
totalBlocks	Blocks found, with blocksLast24h, lastPoolBlockTime and lastPoolBlockHeight beside it.
poolEffort	Work done in the current round ÷ network difficulty. Above 1 is not an error — it means the round has had bad luck so far.
ports	Every port with its starting difficulty, floor and protocol.

Read this first On the shared pool only the block subsidy is divided among miners. The transaction fees in a block stay with the pool, and the 1% fee is taken from the subsidy. So the coinbase total is not what a miner earns: avgBlockReward is. On the solo pool the finder does take the whole coinbase, subsidy and fees, minus the 1% — which is why the two pools report different numbers in the same field. Each pool object states this in sharedRevenue and blockRewardNote so you do not have to remember it.

Endpoints

All under https://b2pool.io. Pool ids are btcb2 (shared) and btcb2-solo.

Path	Returns
/api/v1/public	Both pools, plus a map of every endpoint. Start here.
/api/v1/public/pools	The pool list on its own: {"pools":[…]}.
/api/v1/public/pools/{id}	One pool: {"pool":{…}}.
/api/v1/public/pools/{id}/blocks	Blocks found, newest first. ?page= 0–50, ?pageSize= 1–100. poolFee and minerReward are null while a block is still maturing — the split is not booked until it confirms, and a placeholder there would be a wrong number stated as a fact. subsidy, transactionFees and reward are chain facts and always present.
/api/v1/public/pools/{id}/payments	Payout transactions, newest first. Empty for the solo pool, which pays in the coinbase of its own block.
/api/v1/public/pools/{id}/performance	Hourly hashrate, miners and workers. ?hours= 1–336.
/api/v1/public/network	Chain facts: height, difficulty, hashrate, subsidy, next halving, coinbase maturity.
/api/pools	Alias for /api/v1/public/pools, at the path a Miningcore client asks for on its own. /api/pools/{id} and its sub-paths work the same way.

Every response is JSON with Access-Control-Allow-Origin: *, so a browser can read it directly. Times are ISO 8601 in UTC. Amounts are BTCB2 with 8 decimals, except where a field name ends in Sats. Hashrates are H/s throughout — pool and network alike.

Try it

Nothing to install, nothing to sign up for.

curl -s https://b2pool.io/api/v1/public | jq '.pools[0] | {
  hashrate: .poolStats.poolHashrate,
  miners:   .poolStats.connectedMiners,
  fee:      .poolFeePercent,
  scheme:   .paymentProcessing.payoutScheme,
  reward:   .avgBlockReward,
  network:  .networkStats.networkHashrate
}'

The chain is young, so a tracker may have no other source for its subsidy or difficulty. /api/v1/public/network carries those separately from anything about this pool, and you are welcome to use it that way.

Limits, and what is not in here

Rate limit: 5 / sPer address, burst 20. Over that you get 429, not 503 — we are not down, you are just early. Answers are cached 60 seconds, so polling faster buys you nothing.
Authentication: NoneRead-only, no key, no quota to register for. If you need a higher limit for a legitimate integration, ask.
Stability: AdditiveFields get added, not renamed or removed. The path carries v1; a breaking change would be v2 alongside it.
Not included: Per-miner detailPayments are aggregated per transaction rather than per address, and there is no per-region breakdown. Neither is needed to list a pool, and the chain already holds the payment detail for anyone who wants it.

Found something wrong in the numbers, or need a field that is not here? The pool is small enough that asking works. The protocol notes cover the mining side, and what this chain is covers the rest.