A transpiler you can actually read.

Tessera is a modular quantum circuit transpiler built on top of Qiskit. It takes a logical quantum circuit written against an idealized gate set with no hardware constraints, then produces a physically executable version of that circuit for a real quantum device. That means decomposing gates into the device's native basis, mapping logical qubits onto physical ones, routing around the device's connectivity limits by inserting SWAP gates where needed, and optimizing the result to reduce gate count and depth.

Every circuit in Tessera is represented as a TesseraCircuit : a lightweight intermediate representation that wraps Qiskit's QuantumCircuit and adds pass metadata, backend context, and layout information. Passes operate on this IR directly. Each one receives a TesseraCircuit and returns a modified one, with no shared mutable state between them.

Most transpilers in the quantum computing ecosystem are production systems optimized for correctness and performance across a huge range of hardware and circuit types. That's the right goal for a general-purpose tool, but it comes at a cost. The internals become hard to follow, the pass structure gets entangled, and understanding exactly what happened to your circuit requires digging through thousands of lines of framework code. For researchers, students, and engineers who want to reason carefully about the transpilation process, that opacity is a problem.

Tessera was built to be the opposite of that. It's small enough to read in an afternoon, structured so that each pass does exactly one thing, and designed so that adding a new backend or a new optimization touches as few files as possible. The goal isn't to replace Qiskit's transpiler. It's to give anyone curious about how transpilation actually works a codebase they can trace end-to-end without getting lost.