The Gamut Plotter

Enter the six red, green, and blue x and y coordinates of RGB working space profiles separated by spaces, followed by the profile name [optional], one per line.
Enter colors as css names, hex strings, or css functions, one per line [optional].
To omit a profile, precede it with two slashes: //
The legend may be moved with the mouse.

draw | show axes | white point: D50 D55 D60 D65

Enter the twelve x and y coordinates of CMYK profile cusps separated by spaces, and so on as above.

0.6653 0.3266 0.4762 0.5026 0.1323 0.5179 0.1298 0.1830 0.1876 0.0588 0.5097 0.2352 Gold Fibre Silk //0.6036 0.3381 0.4626 0.4957 0.2470 0.4975 0.1654 0.1981 0.2855 0.1941 0.5022 0.2685 Heavyweight Duo Matt black dimgray

The SVG code:

The cusps of a CMYK profile may be obtained using ArgyllCMS.
The command is iccgamut profile.icc which creates a gamut file profile.gam.
The gamut file contains the Lab coordinates of the cusps in the form:

CUSP_RED "48.338920 78.508402 75.320725"
CUSP_YELLOW "91.485695 -2.705177 116.513023"
CUSP_GREEN "39.337881 -85.333779 6.157227"
CUSP_CYAN "42.771206 -24.650806 -66.584845"
CUSP_BLUE "10.823126 56.617959 -69.110963"
CUSP_MAGENTA "45.503846 82.184014 -10.122959"

Paste the coordinates into the following field, one per line, then get the xy cusps:

CUSP_RED "48.338920 78.508402 75.320725" CUSP_YELLOW "91.485695 -2.705177 116.513023" CUSP_GREEN "39.337881 -85.333779 6.157227" CUSP_CYAN "42.771206 -24.650806 -66.584845" CUSP_BLUE "10.823126 56.617959 -69.110963" CUSP_MAGENTA "45.503846 82.184014 -10.122959"

Paste these twelve x and y coordinates into the coordinates field above, followed by the profile name [optional]:

Chromaticity diagram is loosely based on CIE1931xy blank.svg.
The image is the visual gamut as seen from above.

For more profile coordinates, see RGB Working Space Information at brucelindbloom.com,
and the RawTherapee ICC Profile Creator.