Terms of use
Last updated 2026-10-14.
What this is
Fourier Pen is a free tool made by Jeremy Lee that turns pictures into animated Fourier series drawings. Using it means you accept these terms.
Acceptable use
Use the text prompt feature for drawings you have a right to make. Do not send prompts intended to produce content that is illegal, that harasses a real person, or that the image model's own policies forbid. Do not try to circumvent the rate limits or use the prompt endpoint from anywhere other than this site. The endpoint may refuse requests at any time.
Your content
Pictures you upload stay in your browser and are yours. Drawings, files and videos you save are yours to use however you like. Images returned by the text prompt feature are generated by a third-party model (FLUX.1 schnell on Cloudflare Workers AI, or Google's Gemini if so configured); your use of them is subject to that provider's terms, and generated images may carry a watermark.
No warranty
The site is provided as is, with no warranty of any kind. The maths is correct to the best of the author's knowledge; the edge detection is not, and will miss or invent outlines. Nothing here is guaranteed to work in every browser.
Limitation of liability
To the extent permitted by law, the author is not liable for any loss or damage arising from use of this site.
Changes
This is a free service with a real running cost on the prompt feature. It may change, be rate limited more tightly, or stop at any time without notice. The source is on GitHub under the MIT licence, so you can always run your own copy.