How the tools are built and checked

How a tool is built

1. Method first

   A tool starts as geometry, not as a page: the development method, the datum every dimension is measured from, and the cases where the method stops being valid.

   • Textbook methods only — parallel-line, radial-line and triangulation development, closed-form trigonometry. Nothing from any employer or client.
   • The reference cases are worked out by hand before any code runs, so the code is checked against an answer it did not produce.
   • What the tool does not account for is written down at the same time, and shown on the tool page next to the result.

2. Build

   The geometry is pure code with no interface attached, so the same functions drive the preview, the DXF, the printable template and the tests. Outputs are deterministic and carry a version tag.

   • Same inputs, same file, byte for byte — no timestamps, no randomness in generated geometry.
   • A generator-version comment in every exported DXF, so a part can be traced to the code that made it.
   • All internal maths in millimetres; inches are converted at the edges and tested to round-trip.

3. Verify

   Independent routes to the same answer: hand-derived golden cases, read-back with software that did not write the file, and — where the geometry is the product — a second implementation that re-derives the numbers.

   • Golden cases derived by hand: the 3-4-5 cone gives exactly 216°; the developed arc equals the true circumference; metric and imperial inputs produce identical millimetre geometry.
   • On every release ezdxf 1.4.4 reads back the DXF fixtures and every file the elbow, square-to-round, reducer, cone-segment and pipe tests write — every tool that exports DXF — checking version, units, entity counts, layers and that no entity is zero-length or zero-radius.
   • Renderer-parity suites for nine of the DXF tools: the preview and the exported file are decoded and required to describe the same geometry.
   • A real browser drives every tool — change inputs, download a DXF or CSV, print a template — under the site’s own content-security policy.

4. Release

   A new tool ships only when all of its checks pass in the same run as the rest of the site, and the release can be rolled back in one command.

   • Where the geometry is the product, a second implementation written separately in Python must agree with the first — so far for the K-factor calculator and bend chart, cone in segments, lobster-back elbow, square-to-round and eccentric reducer.
   • New tools cite the published method they follow.

5. Corrections

   When a tool is wrong, the report is reproduced first, a failing test is written for it, and the fix ships with that test, so the same mistake cannot come back unnoticed.