The server does very little. Since ADR/007 Core Application Logic on the Client, the server is primarily a file store: it lists, reads, writes and deletes files, handles authentication, serves the static client, and runs shell commands. When the Runtime API is enabled, it manages a Chrome sub-process and delegates calls to it. This makes the server's implementation language a relatively low-stakes, swappable choice, and over the project’s life it has changed several times.
The server has been, in turn: Node.js (earliest prototypes), then Deno for years, then Go (2025), and now Rust (2026). (The separate move of the client build toolchain from Deno to Node is ADR/009 Client Build Toolchain.) This is further discussed in On Tech Stacks.
Decision
The server is written in Rust (as of v2.10.0). The progression was Node.js -> Deno -> Go -> Rust:
Go (2025): once the server was just a file store, it was rewritten in Go: "significantly less memory and significantly smaller in size."
Rust (2026): the Go server was replaced by an adaptation of the Rust backend used elsewhere in the project, converging the whole codebase on TypeScript + Rust.
Consequences
Positive
Fewer languages. The stack converged from TypeScript + Go + Rust to just TypeScript + Rust: less to master and one backend to maintain.
Leaner runtime. Rust has no garbage collector and produces a small, single statically-compiled binary; memory use drops again.
Opens new doors. A Rust backend makes a future CRDT-based sync engine / real-time collaboration feasible where the Go ecosystem made it impractical — see ADR/002 Sync Engine.
Negative / trade-offs
Churn. Three server rewrites is real effort, and for a while two backends were maintained in parallel before converging.
Steeper language. Rust has a higher learning curve than Go or TypeScript, raising the bar for backend contributors. However, contributions to the backend were rare anyway, and generally unnecessary.
Alternatives considered
Revert the server to TypeScript (Deno or Node). Rejected: a JS runtime buys little for a process that just serves files and it is resource heavy.
Stay on Go. Rejected: Go meant maintaining a backend separate from the project's Rust code, and its ecosystem made the desired CRDT direction impractical.
