About Kouzouki
Kouzouki builds structural engineering calculators that show their work — every equation, every substitution, every code clause on screen, so the result can be checked rather than trusted blindly.
Why this site exists
Most structural design offices run on spreadsheets. They are quick to write and almost impossible to audit. The author leaves, the workbook stays, and three years later nobody can say which edition of the code a given cell was based on, whether a factor was applied twice, or why a hard-coded constant is there at all.
Kouzouki exists to replace that pattern. Each calculator states the standard and edition it works to, prints the governing equation with the actual numbers substituted in, and cites the clause the check comes from. If you disagree with a result, you can see exactly where it came from and check that step by hand.
What is on the site
The suite spans wood design to the AWC NDS and SDPWS, concrete, load-bearing masonry, foundations and geotechnical checks, hydraulics, metal building secondary framing, and conceptual cost estimating. A subset is free to use with no sign-up; the wider suite is available to members.
How the calculators are built
Every engine is written twice. The reference implementation is in Python; a second, independent implementation runs in JavaScript in your browser so results appear instantly without a round trip to a server. The two are held to agreement within a tight tolerance by an automated test suite, so a disagreement between them is treated as a defect rather than a rounding curiosity.
Results are locked down with golden-file regression tests: a large body of known-good outputs is stored and compared on every change, so a refactor cannot silently move a number. Individual adjustment factors are unit-tested in isolation, and boundary conditions are tested deliberately.
Validation against published examples
Testing that software agrees with itself proves only that it is consistent. To show it is correct, engines are checked against worked examples published by standards bodies and established references, and the comparison is published rather than asserted — including where agreement is not exact and why. The Manual J validation write-up is one worked example of that process, documenting a conduction match to 0.00% and explaining the single constant responsible for the residual difference in the total.
Who builds it
Kouzouki is an independent project built and maintained by a structural engineering practitioner who writes software — the tools come directly out of day-to-day design work, which is why they are organised around the checks engineers actually repeat rather than around what is easy to code.
What Kouzouki is not
These are engineering tools, not an engineering service, and using them does not create a professional relationship of any kind.
- No output from this site is a sealed, stamped or certified design.
- Results require review by a qualified engineer before being used on a real project.
- The engineer of record remains fully responsible for the design, the inputs, the applicability of the method, and the governing code edition in their jurisdiction.
- Codes are amended locally. Always confirm the adopted edition and any local amendments.
Full terms are on the terms of use page.
Corrections
Corrections are genuinely welcome — if you believe a calculator is wrong, the report will be investigated and fixed, because a calculator that quietly returns a wrong number is worse than no calculator at all. Custom calculators are also built on request.