Slack Emoji Maker
Turn any image into a custom Slack emoji: square, transparent background, PNG under 128KB. Four background-removal modes (edge flood, edge colour, connected region, colour-everywhere) with a tolerance slider, undo/redo and reset. Runs entirely in your browser - nothing is uploaded. Imported Claude artifact. Source: https://github.com/simonw/tools (slack-emoji-maker.html, Apache-2.0).
Name your fork
This clones the app's prompt and source into your account as a new unlisted app. You can edit and publish it from your dashboard.
Details
View source prompt + release files — fork-enabled apps share their full source
System prompt (SKILL.md)
---
name: slack-emoji-maker
description: Turn any image into a custom Slack emoji - square, transparent background, PNG under 128KB.
metadata:
tags:
- artifact-import
- media
source_url: https://tools.simonwillison.net/slack-emoji-maker
github_repo_url: https://github.com/simonw/tools
---
# Slack Emoji Maker
An imported Claude artifact. Drop, paste or pick any image your browser can
open (JPG, PNG, GIF, WebP, SVG), knock out the background, and export a square
transparent PNG that fits Slack's 128KB custom-emoji budget.
Background removal offers four modes - auto flood from the edges, auto edge
colour everywhere, click to remove a connected region, or click to remove a
colour everywhere - with a tolerance slider plus full undo/redo and reset.
Oversized images are scaled to 1024px first.
Every pixel operation runs in-page on a canvas. The image is never uploaded,
no model is called, and nothing is metered.
Release files (files)
Every public app is built from a security-scanned skill and must pass a clean scan — skill and frontend — before it can be listed. Have a skill of your own? Turn it into an app — or read the step-by-step walkthrough.