To perform the sequence alignment, Alignment Sandbox runs the C tool seq-align directly in the browser using WebAssembly. For details about the compilation from C to WebAssembly, see the biowasm project.
Alignment Sandbox uses the aioli library to run the WebAssembly module in a WebWorker.
Thanks for making this tool, great for teaching. For the sequence: CGACTAGCT and CAGACCTACCTT, with match 3, mismatch -3, gap open extension -2, the local alignment back tracking is not correct. See attached screenshot. The 9 position should be chosen (orange), not 2, then 6 position but not 5. Can you please check what happened to the backtrack code?