Monty is a minimal, secure Python interpreter written in Rust for running code written by AI agents.
It avoids the latency and cost of container sandboxes: a new sandbox starts in under a millisecond and can only reach the host through the functions and mounts you explicitly provide.
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Python 3.14 subset sandbox with no filesystem, environment or network access
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Sub-millisecond sandbox startup from a pool of worker subprocesses
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Host functions and inputs exposed explicitly via external_lookup and inputs
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Serializable snapshots that pause at host calls and resume execution later
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Packages for Python (pydantic-monty), JavaScript/TypeScript (@pydantic/monty) and Rust
Freemium
OSS Monty is free and open source under the MIT License as Python, JavaScript and Rust packages; Full Monty is a commercial server that runs the same sandbox behind a WebSocket with OS-level isolation and horizontal scaling.
Best for
Agent developers implementing code mode or tool chaining who need to run LLM-generated Python safely with minimal overhead.
Not ideal for
Workloads that need full CPython compatibility, third-party packages or arbitrary system access inside the sandbox.
A lightweight, production-ready sandbox from the Pydantic team that makes running agent-written Python cheap and safe.
Monty reached its first stable release, v1.0.0, on September 25, 2026, dropping the experimental label and adding features such as percent formatting and the format() builtin.
As of
Is Monty free?+
Monty is Freemium. OSS Monty is free and open source under the MIT License as Python, JavaScript and Rust packages; Full Monty is a commercial server that runs the same sandbox behind a WebSocket with OS-level isolation and horizontal scaling. Check the official site for current plans.
Is Monty open source?+
Yes - Monty is open source. OSS Monty is free and open source under the MIT License as Python, JavaScript and Rust packages; Full Monty is a commercial server that runs the same sandbox behind a WebSocket with OS-level isolation and horizontal scaling.
How much does Monty cost?+
OSS Monty is free and open source under the MIT License as Python, JavaScript and Rust packages; Full Monty is a commercial server that runs the same sandbox behind a WebSocket with OS-level isolation and horizontal scaling. Pricing changes often - verify on the official site.
Who is Monty best for?+
Agent developers implementing code mode or tool chaining who need to run LLM-generated Python safely with minimal overhead.
Who is Monty not ideal for?+
Workloads that need full CPython compatibility, third-party packages or arbitrary system access inside the sandbox.
What are the best Monty alternatives?+
The closest Monty alternatives on ai.dosa.dev are Pieces for Developers, agenttrace, Vibe Kanban - all listed under Developer Productivity & Workflow.
Who makes Monty?+
Monty is developed by Pydantic. It is listed in the Developer Productivity & Workflow category on ai.dosa.dev.
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