That wasn't so hard. I already have the prototype done. I haven't used Inkscape in a while so watched some beginner tutorials. I'm using Inkscape v1.3.2

Previewing in SendCutSend:

The size I need is CR80 aka ISO/IEC 7810 ID-1

https://en.wikipedia.org/wiki/ISO/IEC_7810
85.60 mm × 53.98 mm (3.370 in × 2.125 in)
Rounded corners with a radius of 2.88–3.48 mm (about 1/8 in). Thickness of . 76 mm thick (I can ignore thickness).

Fortunately the size that I need is already built into Inkscape.

Files > Document Properties
Format: ID card, then rotate

The general shape was easy. Enable snapping, make a rectangle the full size of the document, then round the corners (Rx and Ry input boxes) to 3.5mm. Yay it's a credit card. Path > Object to Path. Then use the node editor to add nodes and create the shim shape.

The art is a trace of some Splatoon splatfest art. I used Inkscape's "freehand" tool to draw over a PNG. These were all open paths (lines that don't connect to a closed shape) so I thicken the line by setting the Stroke width, then Path > Stroke to Path.

Text is handled similarly. Create the text using the text tool. Then Path > Object to Path.

After all the funny shapes are converted to paths, they can be combined together. Now with 1 big Path for all the cutouts, I use Path > Difference to subtract the shapes from the shim shape.

Nice, done!

The biggest pain in the butt was the font. I had a lot of difficulty finding a good free and open source font that was compatible with laser cutting. The font needs to be a stencil with no free-floating islands. Everything that looked good was paid.

There are an infinite number of useless stencil-looking fonts online. I found one called "LaserCut", couldn't find any licensing details, and I had to modify the piece of crap anyway. The "m" has an unnecessary cut just to look cool, while the "o" and "0" had no cuts at all and caused error in SendCutSend! I manually edited the paths to fix "o" and "0".

I'm strongly considering making this myself now. As a follow-up to this project I'll make a laser-cutter-compatible font, free and open source.

FYI there is an open-source font for CNC engraving, but this is not the same requirements as cutting through the object.

Here's some of the prior art that I looked at for design inspiration. The product exists already, even commercially and wallet-sized.

https://www.amazon.com/Wallet-Shim-Credit-Gadgets-Stainless/dp/B0BNM9H776/

https://www.lockpickworld.com/products/shove-it-lock-bypass-tool-for-quick-entry

diff shape with a longer shimming edge, but less grabbing edge, also has a hole
https://grimworkshop.com/products/door-lock-bypass-card

plastic flexible version. I should consider making another out of plastic, the flex could allow it to snaking around door trim and attack the front of the latch
https://modernwarriorproject.com/product/lock-picking-thin-flexible-shims/