// GLOSSARY -- WEB3 INFRASTRUCTURE

What is Sidechain?

1 min read Updated

A sidechain is an independent blockchain with its own consensus mechanism that runs parallel to a main chain and is connected via a two-way bridge — providing scaling but without inheriting the main chain's full security.

WHY IT MATTERS

Sidechains offer scaling through independence. Unlike rollups (which post data to L1 for security), sidechains maintain their own security through their own validators. This means they can be faster and cheaper but don't inherit Ethereum's security guarantees.

The key difference from rollups: if a sidechain's validators are compromised, funds can be stolen. If a rollup's sequencer is compromised, users can still withdraw through L1 because the data is posted there.

Polygon PoS is the most prominent example — technically a sidechain with its own PoS consensus, connected to Ethereum via bridges. It offers very low costs but different security properties than rollups.

FREQUENTLY ASKED QUESTIONS

Sidechain vs rollup?
Rollups inherit L1 security (data posted to Ethereum). Sidechains have independent security (own validators). Rollups are more secure; sidechains are cheaper and can be faster.
Are sidechains less safe?
They depend on their own validator set. A sidechain with many honest validators is reasonably safe. But the security guarantee is weaker than rollups that inherit Ethereum's full validator set.
Is Polygon a sidechain or L2?
Polygon PoS is technically a sidechain. Polygon zkEVM is a true L2 (rollup). The Polygon ecosystem includes both, and the project is transitioning toward ZK-based security.

FURTHER READING

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