db<>fiddle

dbfiddle.uk is a free online SQL playground: write some DDL and some queries, run them against a real database engine, and get a permanent link to the result.

It is similar to tools like SQL Fiddle and rextester, but it is designed specifically to be friendly to markdown-based Q&A sites such as Stack Overflow and Codidact — output is markdown-ready, and the editor is built for longer, multi-step code rather than a single query.

What it does

• Many engines, many versions. SQL Server, Oracle, Postgres, MySQL, MariaDB, SQLite, Db2, DuckDB, Firebird and more. The home page always has the current list.
• Shareable, immutable results. Every run is saved and addressed by a short code. Fiddles are not enumerable, so a fiddle nobody links to is effectively private.
• Sample databases. Some versions come with a ready-made sample schema.
• Real isolation. Executions are against a genuine engine on a disposable VM, so DDL, transactions and server-level behaviour all work as they really do.
• Privacy first. Only the first three octets of your IP are logged. No cookies, no tracking scripts, no fingerprinting. Adverts are self-hosted, so an advertiser only learns you exist if you click.

Fiddles are covered by Creative Commons CC0; the code in this repo is AGPL-3.0 (see LICENSE).

Programmatic access

There is an HTTP API for LLMs. If you are an LLM, go read llms.txt.

How it fits together

The front end is a set of small AWS Lambda functions behind an HTTP API, deployed with AWS SAM (template.yaml):

Most of the application logic lives in the database. The Lambdas are thin: they call a single function in a per-route schema (sql/) and render the result.

Actually executing SQL is the back end's job: the run Lambda POSTs to a separate runner service, which dispatches to a Firecracker microVM per engine and version.

Working on it

The devcontainer (.devcontainer/) provides the AWS SAM CLI, Node and psql. Configuration comes from environment variables — see .devcontainer/.env.sample for the full list.

scripts/local.sh    # install deps, build assets, run the API locally on :3004
scripts/cdn.sh      # bundle and hash static assets, sync to the CDN bucket
scripts/db.sh       # psql shell on the fiddle database
scripts/api.sh      # (re)apply the SQL API
scripts/staging.sh  # deploy to staging.dbfiddle.uk
scripts/prod.sh     # deploy to dbfiddle.uk

Static assets are content-hashed at build time. scripts/cdn.sh writes layer/shared/manifest.json, basename to hashed name, and pages resolve every static URL through asset() in layer/shared/shared.mjs. The manifest is not committed; a deploy that skips scripts/cdn.sh fails on the missing file.

Back end

Every engine version runs in a Firecracker microVM (see run/) restored from a snapshot for each fiddle. run/cumbria.md is a rough and ready guide to setting up the host.