What Are Starknet Appchains? Madara and Custom Rollups Explained

Starknet appchains are custom, application-specific rollups built using Starknet's technology stack — most notably the Madara sequencer client — allowing a project to launch its own dedicated zero-knowledge rollup rather than deploying as just another contract on the shared Starknet mainnet.

This mirrors a broader trend across the rollup ecosystem: as frameworks for launching custom chains have matured (see our overview of launching your own L2 rollup), more teams with significant, specific throughput or customization needs are choosing dedicated chains over shared general-purpose ones. Starknet's version of this uses Cairo, its own zero-knowledge-friendly programming language and proof system, rather than Ethereum's standard EVM.

What Madara actually is

Madara is an open-source sequencer client, built using the Substrate framework, that implements Starknet's execution and state model — allowing a team to run their own Starknet-compatible chain rather than relying on the shared Starknet mainnet sequencer. It's the core piece of infrastructure that makes launching a Starknet appchain practical without building an entire zk-rollup client from scratch.

Because Madara-based appchains use the same underlying execution environment (Cairo, Starknet's account and fee model) as Starknet mainnet, developers building on an appchain can often reuse tooling, contract patterns, and developer knowledge from the broader Starknet ecosystem, rather than learning an entirely separate stack.

Why a project would want a dedicated Starknet appchain

• Dedicated throughput. An appchain isn't competing with unrelated Starknet mainnet traffic for block space, which matters for applications with high, latency-sensitive transaction volume — certain gaming or high-frequency trading use cases, for example.
• Custom configuration. Appchains can adjust gas token choice, fee models, and permissioning in ways a shared mainnet deployment can't.
• Data availability flexibility. Like other rollup frameworks, Starknet appchains can choose where to post data — settling fully to Ethereum for maximum security, or using a cheaper alternative data-availability approach with a different trust trade-off (similar in spirit to the validium model discussed in our piece on how L2s inherit Ethereum's security).
• Revenue capture. Running your own sequencer means capturing sequencer fee revenue directly rather than paying it to a shared chain's operator.

The trade-offs

The same fragmentation concerns that apply to any dedicated rollup apply here: a Starknet appchain starts with its own isolated liquidity, requiring bridging for users to move assets in from Ethereum or Starknet mainnet, and it takes on the operational responsibility of running sequencer infrastructure (or contracting that out — see our explainer on Rollup-as-a-Service, a model that also applies to Starknet-based chains through relevant providers).

Cairo's differences from Solidity are also a real consideration. Teams with an existing EVM/Solidity codebase face a genuine porting effort to deploy on any Starknet-based chain, appchain or mainnet — this is different from, say, choosing an OP Stack-based appchain, where existing EVM contracts typically deploy with little modification.

Consideration	Starknet mainnet	Starknet appchain (Madara)
Block space	Shared with all Starknet activity	Dedicated to your application
Liquidity	Established, shared ecosystem	Starts isolated, needs bridging
Sequencer control	Starknet's shared sequencer	Operated by your team (or a RaaS provider)
Execution environment	Cairo/Starknet account model	Same Cairo/Starknet model

Where this fits in the broader L2 landscape

Starknet appchains are Starknet's answer to a question every major rollup ecosystem is answering in its own way — Optimism with the OP Stack and Superchain vision, Arbitrum with Orbit, Polygon with CDK and AggLayer. Each takes a different technical approach (optimistic vs. zk, EVM vs. Cairo) but shares the same underlying bet: that dedicated, app-specific chains built on a common, well-audited framework will outcompete both fully custom blockchains (too slow and expensive to build safely) and shared general-purpose chains (too congested and inflexible for some use cases) for the right applications.

What to check before building or transacting on one

Because appchains vary widely in their specific configuration, it's worth verifying directly: what data-availability model does this specific appchain use, and what's the actual trust assumption if it's not posting full data to Ethereum? Is the sequencer centralized, and if so, what's the plan to decentralize it? What's the chain's real, current liquidity and user base, distinct from Starknet mainnet's own numbers? These questions apply to any dedicated rollup, and Starknet appchains are no exception just because they share a technical lineage with a well-established mainnet.

Bottom line

Starknet appchains, built with tools like Madara, let developers launch dedicated Cairo-based rollups with their own sequencer, gas token, and configuration — trading shared liquidity and tooling maturity for dedicated throughput and customization. They're a good fit for applications with a clear, validated need for dedicated block space, and a poor fit for early-stage projects still figuring out product-market fit on a shared chain.