What Is the Stratum Protocol? How Miners Talk to Pools

Published July 22, 2026, 19:00 UTC

Every time a miner connects to a pool, they speak a common language called Stratum. It is the protocol that carries work down to your machine and shares back up to the pool, and it has quietly underpinned nearly all pooled and solo mining since 2012. This guide explains what Stratum is, the exact messages that flow across the wire, how difficulty and shares work, and where the newer TLS and Stratum V2 variants fit in.

Why Stratum exists

Before Stratum, miners polled the node with getwork and later getblocktemplate, repeatedly asking, "is there new work yet?" That was chatty and slow. Stratum flipped the model: the pool pushes new jobs to the miner the instant they are ready, and the miner streams shares back. It is efficient, it scales, and it is why one pool can serve thousands of machines over a single lightweight TCP connection each.

The Stratum V1 handshake, step by step

Classic Stratum V1 is a line-based JSON-RPC protocol. A session looks like this:

subscribe. The miner opens a TCP connection and sends mining.subscribe. The pool replies with a subscription id and the extranonce data the miner will use to make its work unique.
authorize. The miner sends mining.authorize with a username, which on a solo pool is your own wallet address, optionally with a worker name. On mkpool the password is just x.
set_difficulty. The pool sends mining.set_difficulty, telling the miner how hard each share must be. This can change at any time.
notify. The pool sends mining.notify with a job: the previous block hash, the coinbase parts, the merkle branches, and a flag for whether to drop old jobs. Every new network block triggers a fresh notify.
submit. When the miner finds a header below the target, it sends mining.submit with the nonce and timestamp. The pool checks it and returns accepted or rejected.

That loop, notify then submit, repeats for as long as you mine. It is elegant and simple, which is exactly why it spread everywhere.

Shares, difficulty, and vardiff

A share is a solution that meets the pool's difficulty target, not necessarily the network's. Think of difficulty as how many leading zeros the hash needs. Shares prove your miner is working and let a pool measure your contribution. Every so often a share happens to clear the far higher network target, and that is a real block.

Vardiff (variable difficulty) keeps this practical across wildly different hardware. A Bitaxe and an Antminer differ by two orders of magnitude in hashrate, so the pool hands each a difficulty that produces a sensible share rate: low for the Bitaxe so it still reports in regularly, high for the Antminer so it does not flood the connection. If you would rather pin a fixed value, most pools also offer fixed-difficulty ports, a choice we break down in our guide to picking the right tier on the connect page.

The problem with plain Stratum V1

Stratum V1 has one glaring weakness: it is plaintext. Your payout address, worker names, and every message travel readable across the internet. On an untrusted network a passive observer learns everything about your operation, and an active attacker can rewrite the session to redirect your hashrate to their own account while you see normal-looking accepted shares. This is not hypothetical; plaintext hashrate hijacking has been demonstrated many times.

Two modern fixes: TLS and Stratum V2

There are two ways to close that hole:

Stratum over TLS. Wrap the same V1 protocol in a TLS tunnel, exactly like HTTPS does for the web. It is a one-setting change on most firmware and stops both snooping and hijacking. Our Stratum TLS guide covers it end to end.
Stratum V2. A ground-up redesign that replaces JSON with compact binary framing, encrypts every session with the Noise protocol, authenticates the pool with a published authority key, and can even let miners choose their own transactions. It is the direction the whole industry is moving, explained fully in Stratum V2 explained.

Stratum in solo mining

Solo mining uses the exact same protocol. The only difference from a shared pool is accounting: on a solo pool your address is your account, and a share that solves a block pays the whole reward to you. Whether you run a Bitaxe or a farm, the Stratum conversation is identical, which is why the same firmware talks to any compliant pool. To see it in action, pick a chain on the connect page and point a miner at it, then read what solo mining is for the economics behind those shares.

Frequently asked questions

What is the Stratum protocol?

Stratum is the communication protocol between a miner and a mining pool. The pool pushes work (block templates and jobs) to the miner, and the miner submits shares back as proof it is hashing. It replaced older getwork and getblocktemplate polling with an efficient push model and is now the near-universal standard.

What does a Stratum share actually contain?

A share is a submitted block-header solution that meets the pool's current difficulty target. It proves the miner did a known amount of work. Most shares are only good enough for the pool's target, but occasionally a share is good enough to satisfy the network target, which means it solves a real block.

What is the difference between Stratum V1 and Stratum V2?

Stratum V1 is the original 2012 JSON protocol: simple, universal, and unencrypted. Stratum V2 is a modern redesign that encrypts the session with Noise, authenticates the pool with a public key, uses compact binary framing, and can let miners choose their own transactions. V2 is more secure and more efficient.

What is vardiff in Stratum?

Vardiff, or variable difficulty, means the pool automatically raises or lowers the share difficulty to match your hashrate. A small miner gets low difficulty so it still submits shares regularly; a big miner gets high difficulty so it does not flood the pool. It keeps the share rate in a healthy range for any device.

Is the Stratum protocol encrypted?

Plain Stratum V1 is not: everything travels as readable JSON, which is why it can be sniffed or hijacked on an untrusted network. You can wrap V1 in TLS for encryption, or use Stratum V2, which builds encryption and pool authentication into the protocol itself.

What port does Stratum use?

There is no single fixed port; pools publish their own. mkpool uses ports in the 3300 to 3400 range, with different ports for vardiff, fixed difficulty tiers, TLS, and Stratum V2. The connect page for each chain lists every port and what it is for.

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← back to all articles

What Is the Stratum Protocol? How Miners Talk to Pools

Why Stratum exists

The Stratum V1 handshake, step by step

Shares, difficulty, and vardiff

The problem with plain Stratum V1

Two modern fixes: TLS and Stratum V2

Stratum in solo mining

Frequently asked questions

What is the Stratum protocol?

What does a Stratum share actually contain?

What is the difference between Stratum V1 and Stratum V2?

What is vardiff in Stratum?

Is the Stratum protocol encrypted?

What port does Stratum use?

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Keep reading

Where to Buy a Bitaxe in 2026: Trusted Vendors and Models Compared

What Is a Bitaxe? The Open-Source Solo Miner Explained

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Why Stratum exists

The Stratum V1 handshake, step by step

Shares, difficulty, and vardiff

The problem with plain Stratum V1

Two modern fixes: TLS and Stratum V2

Stratum in solo mining

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