About StackTools

Fast developer utilities that run entirely in your browser — no signup, no friction.

StackTools is a collection of free online tools for developers: format JSON, decode JWTs, convert curl to fetch, generate hashes and UUIDs, explore the JavaScript event loop visually, and more.

Our flagship JavaScript Execution Visualizer helps students and interview candidates understand call stacks, microtasks, macrotasks, hoisting, and closures step by step.

Browse the full catalog on the tools directory or read practical explainers in our guides.

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