Rustbox vs E2B: Choosing a Sandbox for AI Agents and Untrusted Code

The choice comes down to workload scope: Are you building a persistent workspace for an agent, or a fast execution boundary for a product?

E2B describes its sandbox as a fast, secure Linux VM created on demand for agents. Its SDK and documentation are directed at building coding agents, executing file operations, operating full interactive shells, and handling complex multi-step developer operations.

Rustbox is designed to be narrower and faster. You send a code payload, choose one of the curated languages, pass optional standard inputs, and receive a structured result with stdout, stderr, execution time, memory usage, limits, and a specific verdict (e.g. `accepted`, `time_limit`, `memory_limit`, `runtime_error`).

E2B relies on Firecracker-powered microVMs. This model isolates execution at the VM level, providing standard Linux file layout, shells, and package capabilities inside an isolated virtual container. It is a powerful pattern when an agent behaves like a human developer—running arbitrary packages, running custom background tasks, or interacting with a virtual disk.

Rustbox focuses on a secure sandbox boundary optimized specifically for rapid-fire code runs. The internal architecture uses kernel-level isolation (utilizing cgroups, namespaces, and seccomp profiles) to control CPU, memory, processes, and network egress boundaries. To preserve our strict defensive posture, this article intentionally does not repeat the exact sandbox construction details, as our architecture represents a core element of Rustbox's defense-in-depth model.

WORKLOAD latency is highly dependent on environment startup. This is where the product shapes diverge significantly.

For repeated, high-frequency executions where a user is waiting in real time (such as clicking "Run Code" on an assessment screen or evaluating an LLM tool call synchronously), Rustbox's execution pipeline eliminates startup delays. E2B is optimized for scenarios where an environment stays warm for minutes while an agent interacts with it.

E2B provides maximum environment flexibility. It supports custom Docker templates, letting you pre-bake specific operating system dependencies, packages, and startup files. If your agent requires a complex toolchain (e.g. LaTeX engines, custom databases, or arbitrary compiled binaries), E2B lets you construct a tailored VM template.

Rustbox supports a curated catalog of 8 languages: Python, C, C++, Java, JavaScript, TypeScript, Go, and Rust. By targeting the primary languages used in assessments, standard coding platforms, and common developer SDKs, we maintain high optimization and instant resource pooling. The tradeoff is simple: less arbitrary customization, in exchange for predictable, high-performance execution.

E2B allows full outgoing network access by default, which can be custom-routed or disabled. Its persistence model supports pausing and resuming sandboxes, preserving disk and memory state across hours.

Rustbox executes jobs as isolated runs. In `judge` mode, the network namespace is closed by default to guarantee security and prevent data exfiltration. In `agent` mode, outgoing connections are securely routed through our embedded proxy, allowing controlled HTTPS connections (port 443 only) with strict byte caps and rate limits.