DB Fiddle
db-fiddle.com
Run a schema and a query against real MySQL, Postgres or SQLite
No sign-up
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db-fiddle.com
Run a schema and a query against real MySQL, Postgres or SQLite
aistudio.google.com
Prompt playground with model, temperature and system-prompt controls
hoppscotch.io
Sends HTTP, GraphQL and WebSocket requests from a browser tab
mail-tester.com
Send one email to the address it gives you and get a spam score out of ten
mailinator.com
Any address at mailinator.com already has an inbox you can read without signing up
mailtrap.io
Catches the emails your app sends in a fake inbox so no real person gets them
regex101.com
Builds and explains a regular expression while you type it
webpagetest.org
Loads your page from a chosen city and browser and films the result
Cuts across
A tag is orthogonal to the category tree — that is what makes it worth having.