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What Is a Sidechain?

A sidechain is its own blockchain that talks to a parent chain through a peg or bridge. It has its own miners or validators, its own rules, and its own failure modes. Coins "move" by locking on one side and minting a representation on the other. Polygon PoS, historically, is the example people mean. A Layer 2 rollup is a different animal: it posts data back to Ethereum so Ethereum can reconstruct state. A sidechain asks you to trust its own validator set.

How It Actually Works

• Lock-and-mint or a federated peg connects the two ledgers. Speed and cheap fees come from not waiting on the parent for every transaction.
• Security does not automatically inherit. If the sidechain's validators collude or the bridge contract fails, the pegged asset is an IOU on a crime scene. Same lesson as bridges generally.
• Teams blur the words "L2," "sidechain," and "appchain" because "L2" sells. Ask where data lives and who can halt the chain.

Risks and Common Mistakes

• Parking size on a sidechain because fees are cute. Cheap is not inherited security.
• Wrong-network sends. Addresses look the same. The state machines do not.

When It Matters

Any time a product says it is "on Ethereum" and the fine print is a different validator set. Check L2Beat for the rollup side of that spectrum.

Related Terms

• Layer 2
• Bridge
• Data availability

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