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This fun little tool is mostly meant for role playing purposes, but if you find other uses for it, all the better. The tool is simple: Pick a summoning circle, click the circles to select them, click on runes in the menu to add them to the selected circle, change the colors as desired, click 'Summon a demon' to receive a randomized description of a demon, one which holds no bearings to the runes you've used, and you're done. Of course, you could use the circles as magical summoning circles for non-demons, as strange security mechanisms only the right runes can unlock, or for all sorts of other purposes. There's a lot of fun to be had with this, so let your imagination run wild.
With the 'turn to image' button you can turn the summoning circle you've created into a single image. It'll appear at the bottom as soon as you've clicked the button. Do note that the runes will be slightly smaller, this is done to ensure everything still looks alright.
If you need printable versions (for personal use only), here are two pdfs:Runes