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What is a sidechain?
A sidechain is a separate blockchain that runs alongside a main chain such as Ethereum, with its own validators and consensus rules, and is linked to it by a two-way bridge. Unlike a rollup, it does not post its transaction data back to the main chain.
What it means for you
A sidechain's security comes from its own validators, not from Ethereum, so if they act dishonestly Ethereum cannot correct it. Tokens moved there through the bridge are usually burned on one side and minted on the other, so their value depends on that bridge and its contracts working as intended.
A common mistake: “A sidechain is a kind of layer 2, so it has Ethereum's security.”
In fact: ethereum.org notes sidechains do not inherit Ethereum's security; they rely on their own validators. A rollup, by contrast, posts its transaction data to Ethereum.
How it works
A sidechain runs its own consensus, such as proof of authority, delegated proof of stake or a Byzantine-fault-tolerant scheme, and sets its own block parameters, which is how it reaches faster blocks and lower fees. Many sidechains are EVM-compatible, so Ethereum contracts can be deployed unchanged. A two-way bridge moves value by burning on one side and minting on the other. Because it relies on its own validators, a coordinated group of malicious validators could compromise the chain, and Ethereum's security does not extend to it.
Source: ethereum.org: Sidechains · checked 4 October 2026
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