Open-source AI dev-tools

Four small tools for making the Claude API legible — observe a single call, replay an agent trace, compare prompts side by side, build a tool-use loop interactively. Same design language, distinct angle each.

context-lens

context-lens

See a Claude prompt before you ship it — tokens, context-window position, cost, caching boundaries.

claudoscope

claudoscope

X-ray your Claude API calls: prompt caching, tokens and cost, visualized live.

agent-replay

agent-replay

Replay a Claude agent's tool-calling loop, step by step on a cinematic timeline.

prompt-lab

prompt-lab

A/B test your Claude prompts side by side — output, cost and latency, compared.

tool-lab

tool-lab

Interactive Claude tool-use sandbox — define tools, mock responses, watch the agent loop live.

Read the writing

Each tool has one or two long-form posts explaining the engineering decision behind it — the protocol-level details, the failure modes it surfaces, and what it changes about how you ship.