Free online developer tools

47 tools

Small utilities developers reach for daily: JSON and YAML formatters, Base64 and URL encoders, regex testers, JWT decoders, diff viewers and cron helpers. Prefer tools marked as running in your browser when you paste tokens, keys or production data, because nothing is uploaded.

Showing 1–24 of 47

0.550score
Web Worker vs Main Thread Benchmark
MiladSadeghi
Crunches 50,000 log lines either on the main thread or in a Web Worker, so you can feel the difference in UI blocking.
ArtifactNo sign-upIn-browser★ 4developer tools
0.530score
Local Text Compare
JayAnthKolli46
Side-by-side comparison and merging of text, code, Word, PowerPoint and PDF files, running offline, with extra text clean-up commands.
ArtifactNo sign-upIn-browser★ 1developer tools
0.478score
Chrome Built-in Model Playground
Simon Willison
Runs prompts against the language model built into Chrome, downloading it on first use.
ArtifactAINo sign-upIn-browserdeveloper tools
0.478score
Linux in the Browser
Simon Willison
Boots a small Linux image through the v86 x86 emulator so you can run shell commands in a tab.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
Mermaid to ASCII
Simon Willison
Renders Mermaid flowcharts and sequence diagrams as Unicode box-drawing text using a WebAssembly library.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
Mermaid to Unicode Box Art
Simon Willison
Renders Mermaid flowchart and sequence diagrams as terminal-style Unicode box art in the browser.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
MicroPython Sandbox
Simon Willison
Runs MicroPython in WebAssembly and stores the code in the URL so snippets are easy to share.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
MicroQuickJS Sandbox
Simon Willison
Executes ES5-style JavaScript in a small WebAssembly engine and keeps the code in the page address.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
Python Comment Stripper
Simon Willison
Removes comments from Python code using the real tokenizer on Pyodide, leaving strings and docstrings intact.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
Python REPL in the Browser
Simon Willison
An interactive Python prompt running on Pyodide with several runtime versions and command history.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
QuickJS Sandbox
Simon Willison
Runs JavaScript inside a QuickJS WebAssembly sandbox with a synchronous fetch helper and example snippets.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
Redis Array Playground
Simon Willison
Runs the Redis AR* array commands against an in-memory instance compiled to WebAssembly.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
SLOC Counter
Simon Willison
Counts source lines by language from pasted code, a GitHub repo or a ZIP and estimates effort with COCOMO.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
SQLite AST Viewer
Simon Willison
Parses SQLite SELECT queries into an abstract syntax tree shown as JSON and Python.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
SQLite Bytecode Explorer
Simon Willison
Shows the VDBE bytecode SQLite generates for a query, using EXPLAIN.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
SQLite Output Formatter
Simon Willison
Runs SQLite in WebAssembly and shows query results in about twenty formats including boxes, CSV, JSON and Markdown.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
SQLite Query Explainer
Simon Willison
Runs a query in browser-based Python SQLite and annotates EXPLAIN and query plan output in plain English.
ArtifactNo sign-upIn-browserdeveloper tools
0.478score
SQLite Syntax Playground
Simon Willison
Formats, parses, validates and tokenizes SQLite SQL in the browser using a compiled parser.
ArtifactNo sign-upIn-browserdeveloper tools
0.477score
APSW SQLite Query Explainer
Simon Willison
Analyzes SQLite queries with APSW running in an in-browser Python environment.
ArtifactNo sign-updeveloper tools
0.477score
Bugzilla Bug Viewer
Simon Willison
Displays a Bugzilla bug with its comments and history as a clean timeline.
ArtifactNo sign-updeveloper tools
0.477score
Claude Code Timeline Viewer
Simon Willison
Shows a Claude Code session .jsonl file as a searchable, filterable timeline.
ArtifactNo sign-updeveloper tools
0.477score
Claude Token Counter
Simon Willison
Counts tokens for text and image attachments across several Claude models using Anthropic token-counting API and your key.
ArtifactAINo sign-updeveloper tools
0.477score
Clipboard Viewer
Simon Willison
Shows every format present on your clipboard after a paste, including text, HTML and images.
ArtifactNo sign-updeveloper tools
0.477score
Codex Session Timeline Viewer
Simon Willison
Opens a Codex rollout .jsonl file as a searchable, filterable timeline.
ArtifactNo sign-updeveloper tools