An error budget sets the maximum allowed probability that a quantum algorithm fails during execution. In resource estimation, it is a constraint alongside the program and the assumed fault-tolerant architecture. section 9.4
The budget shapes the estimated implementation by requiring the estimator to:
- Search for error-correction and magic-state-distillation parameters that execute the program within the permitted failure probability. section 9.4
- Translate logical resource demands—including qubits, gates, measurements, and circuit depth—into physical resource estimates. section 9.4

