Bolt is StackBlitz’s AI-powered full-stack development environment that runs entirely in the browser using WebContainers technology, which executes a real Node.js runtime inside a WebAssembly sandbox without any local installation. Since launching in October 2024, Bolt has attracted more than 7 million users and reached $40 million in annualized recurring revenue by March 2025, earning a $700 million valuation and a $135 million Series B in January 2025. A May 2026 Microsoft Azure partnership expanded Bolt’s cloud deployment capabilities, and Claude Sonnet 4 was rolled out as the primary model for code generation.
Key capabilities
WebContainers in-browser runtime — Bolt runs a full Node.js environment inside the browser tab using StackBlitz’s WebContainers technology, allowing it to install npm packages, execute build tools, and serve a live preview without a remote server or local machine involvement.
Multi-model AI code generation — Bolt supports Claude, GPT-4o, and Gemini as generation backends, letting users switch models mid-project or choose based on task type. The agent handles multi-file edits, refactoring, and iterative feature development from natural-language instructions.
Integrated terminal and live preview — A full terminal pane and live browser preview run alongside the editor, giving developers immediate feedback on generated code with the ability to run commands, inspect logs, and interact with the running application in the same interface.
bolt.diy open-source self-hosted variant — StackBlitz maintains bolt.diy as a fully open-source, self-hostable version of Bolt that allows teams to run the environment on their own infrastructure, bring their own API keys, and customize the agent behavior without platform restrictions.
Autonomy level
Bolt operates at autonomy level 4. When given a description of an application or a change request, the agent plans the implementation, writes code across multiple files, installs dependencies, runs the application inside WebContainers, and iterates on visible errors without requiring step-by-step human guidance. The developer supervises outcomes and provides high-level direction, but implementation — including debugging cycles — is handled autonomously by the agent.
Strengths
- Entirely browser-based with zero local setup; the full development environment loads in a tab
- WebContainers executes real Node.js, enabling authentic package installs and build processes in-browser
- 7 million users and $40 million ARR demonstrate broad adoption and platform viability
- bolt.diy open-source variant gives teams a self-hosted option with full customization
- Microsoft Azure partnership adds enterprise-grade deployment targets
- Multi-model support (Claude, GPT-4o, Gemini) provides flexibility for different generation tasks
Limitations
- Browser-only — there is no local development mode or desktop client
- WebContainer sandboxing limits certain server-side operations such as native binaries and some filesystem behaviors
- Generated applications typically require significant refinement before they are production-ready
- Free tier imposes token and compute limits that constrain longer or more complex projects
- Primarily suited for greenfield web applications; integration into large existing codebases is not a supported workflow