Free online developer tools

4 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 1–4 of 4

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
0.477score
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
llm-lib Demo
Simon Willison
Try one JavaScript library against OpenAI, Anthropic or Gemini models by picking a provider and pasting a key.
ArtifactAINo sign-updeveloper tools
0.477score
OpenAI Prompt Caching Playground
Simon Willison
Sends prompts with different structures to OpenAI and shows how many tokens were served from cache.
ArtifactAINo sign-updeveloper tools