A mining pool is a work-distribution and reward-accounting service. The pool or job negotiator gives miners candidate work, miners return lower-difficulty shares that prove contributed hash rate, and a rare share below the Bitcoin network target becomes a valid block candidate. Pool shares are accounting evidence, not blocks, and pool control over job construction does not give authority over the consensus rules enforced by full nodes.
Solo mining has extremely high variance: a miner earns the whole block reward when it finds a block and nothing otherwise. A pool aggregates many miners and redistributes revenue according to measured contributions. The pool does not lower Bitcoin difficulty; it only makes income statistically smoother by sharing rare block events across participants.
Mining jobs originate from a block template or an equivalent construction pipeline. BIP22/BIP23 describe getblocktemplate-based work, while pool protocols distribute header-related fields, coinbase data and search-space parameters to workers. The miner hashes candidate headers; only a result satisfying consensus proof of work can become a block.
A share is a hash result below a pool-defined target that is much easier than the network target. Shares let the pool estimate how much probabilistic work each worker supplied over time. They are not added to the blockchain and do not create confirmations; they are metering records for reward accounting.
Pools deliberately set a share target so miners submit proofs frequently enough for measurement. Bitcoin's network target is far harder. A share that meets only the pool target earns accounting credit; if the same hash also falls below the network target, it is a block candidate. Variable difficulty changes submission frequency, not Bitcoin consensus difficulty.
PPS pays a fixed expected amount per accepted share and moves block-finding variance to the pool operator. FPPS typically adds an estimate of transaction-fee revenue to the expected subsidy component. PPLNS rewards shares within a recent work window when blocks are actually found, leaving more variance with miners. Exact formulas, fees, reserves and orphan handling are pool-specific and must be checked rather than inferred from the label alone.
In conventional pooled mining, the pool commonly constructs the block template and chooses the coinbase payout destination; miners mainly search the assigned space. That gives the pool influence over transaction selection and block construction but not the power to make invalid blocks valid. Full nodes independently validate any block the pool publishes.
Stratum V1 became the dominant practical protocol for distributing mining work but leaves substantial template control with the pool. Stratum V2 separates roles more cleanly, supports encrypted/authenticated transport and includes job-negotiation mechanisms intended to let miners construct or select more of their own block templates, reducing single-operator transaction-selection power when deployed.
Pool concentration matters because a small set of coordinators can influence transaction inclusion, software rollout and short-term hash distribution. But pool hash rate is not identical to miner ownership: miners can redirect machines to another pool. Concentration still creates real coordination and censorship risks, especially if switching costs, contracts or firmware integration reduce that mobility.
Shares can be rejected because they are stale, duplicate, malformed or outside the assigned job. Propagation latency between miner and pool, slow job updates and network instability increase wasted work. Pool-side stale-share rate therefore measures operational efficiency, but it is distinct from stale blocks on Bitcoin's chain.
A miner should verify pool fees, payout scheme, minimum payout, payout transaction policy, share difficulty, reject/stale rates, server endpoints, failover behavior, firmware compatibility and whether transaction-selection control sits with the pool or the miner. For meaningful revenue, compare expected payout against observable accepted shares and on-chain pool blocks rather than trusting dashboard labels alone.
For the clearest picture, read this entry together with Mining, Hashrate, Braiins Pool, Stratum V2, Mining Share, Pay Per Share. The reverse links also lead from Coinbase transaction, Marek “Slush” Palatinus, Braiins Pool, Stratum V1.