> ## Documentation Index
> Fetch the complete documentation index at: https://docs.classiq.io/llms.txt
> Use this file to discover all available pages before exploring further.
# Fault-Tolerance Engine
The Fault-Tolerance (FT) Engine lowers a logical quantum circuit onto a 3-D surface-code
lattice and estimates the logical error rate you would observe when running it on
error-corrected hardware. You use it to explore how a circuit behaves under a physical
noise model and how much its logical error improves as you increase the code distance.
Here's a routed program rendered by the engine — drag to orbit, scroll to zoom, and toggle between the surface-code and logical views:
**This viewer is fully interactive — go ahead and play with it!** Drag to orbit, scroll to zoom, right-drag to pan, and switch between the surface-code and logical views.
The workflow runs in four stages, each covered on its own page:
Turn a physical noise description into logical error-rate information.
Lower a transpiled Clifford+T circuit onto the surface-code lattice.
Render the routed program as an interactive 3-D visualization.
Combine routing and noise to estimate total error across code distances.
The stages are sequential: the routed program and the logical noise feed the final error
estimate. For the full API, see the
[Error Correction SDK reference](/sdk-reference/error-correction).