This is a Javascript program for designing Celtic knots. Initially the display is a simple weave of intersecting threads. You can design a knot by clicking on the points where the threads intersect. The program ensures that your knot is always properly woven (over then under). Your knot will look best if it has some symmetry or pattern to it (for bonus points, use a single thread).

Click once on any intersection point to make a horizontal cut. The threads rejoin and now run horizontally past the point. Click again to make a vertical cut, making the threads run vertically past the point. Click a third time to restore the point to its original state with the threads running diagonally through it. If you want to draw a smaller knot, just cut around its perimeter.

This program only helps with rectangular knots, not circles or triangles. It also has quite limited drawing skill. For example, click “Demo” and compare the long curves in its central knot with the hand-drawn ones in the original (click on the icon there to see the knot being drawn). However, you can get a pretty good idea of what a rectangular knot would look like if drawn well.

There are three standard reference books about drawing Celtic knots. The simplest and most recent is Iain Bain's Celtic Knotwork (published in 1986, ISBN 0-8069-8638-7). More comprehensive, but less accessible, is his father’s book Celtic Art, the Methods of Construction by George Bain (published in 1951, ISBN 0-0946-1830-5). The earliest standard reference is Celtic Art in Pagan and Christian Times by J. Romilly Allen (published in 1904, Methuen & Co.).

This copy of the program uses a 30 by 20 grid of squares. If your design needs more space, use the large version, which has finer threads and a 60 by 40 grid.

If you like this sort of design, it’s worth visiting Direct Imagination, who publish a CD-ROM version of the wonderful Grammar of Ornament.