Vardiff (Variable Difficulty)

Vardiff, short for variable difficulty, is the system a mining pool uses to automatically set and adjust the share difficulty assigned to each connected miner. Rather than handing every device the same target, the pool raises or lowers your personal target based on how fast you find shares, aiming for a steady submission cadence regardless of whether you run a tiny hobby board or a large fleet.

Why pools use vardiff

A good difficulty has two jobs. It must be easy enough that your miner submits shares regularly, so the pool can estimate your hashrate and pay you smoothly. It must also be hard enough that the pool is not flooded with submissions from thousands of workers, which would waste server resources. Vardiff balances these by targeting a submission roughly every couple of seconds, scaling the target up for powerful machines and down for small ones.

What miners see

When vardiff raises your difficulty, you submit fewer but heavier shares; your expected payout is unchanged because each share counts proportionally more. During the brief moment a difficulty change takes effect, a small burst of rejected or stale shares is normal as the miner catches up to the new target. Low-power devices such as a single open-source board especially benefit, because vardiff prevents them from spamming easy shares.

The value vardiff is tuning is the worker's share difficulty, and transient changes can momentarily bump your reject rate.