Bun vs Deno for Solo Developers

Quick Comparison

Bun Overview

Bun is the speed-focused JavaScript runtime built in Zig with JavaScriptCore. It's designed as an all-in-one toolchain: runtime, bundler, package manager, test runner, and TypeScript handler in one binary. The whole pitch is performance and developer experience improvements over Node.

Bun targets Node compatibility aggressively. It reads package.json, installs from npm, supports CommonJS and ES modules, and implements most Node built-in modules. The goal is "Node, but faster and with batteries included." If you know Node, you know Bun.

For solo devs, Bun is appealing because the iteration loop is faster, the toolchain is unified, and the migration cost from Node is low. You don't need to learn new APIs or restructure your imports. You just swap node for bun and most things work.

Deno Overview

Deno is the security-first, web-standards-first JavaScript runtime created by Ryan Dahl (also Node's creator). Deno was built to fix the things Dahl regretted about Node: the lack of security, the divergence from web standards, the npm-centric module system.

The original Deno used URL-based imports instead of npm, ran with explicit permission flags (no filesystem or network access without --allow-read or --allow-net), and shipped with TypeScript as a first-class citizen. Web standards like fetch, WebSocket, and Web Crypto were the runtime APIs, not third-party modules.

Deno 2, released in late 2024, was the pragmatism update. Full npm compatibility (you can deno install npm:react), package.json support, node_modules folder support, and a workspaces system. The web standards stayed, but the "no npm" stance softened to "npm works, but JSR is recommended."

Key Differences

Engine choice has performance implications. Bun uses JavaScriptCore, the engine in Safari. Deno uses V8, the engine in Chrome and Node. V8 is more aggressively optimized for long-running server workloads. JavaScriptCore has faster startup. For short-lived tasks like CLI tools or serverless functions, Bun usually wins. For long-running servers under load, the performance is close, sometimes V8 (Deno) wins.

Security model is the biggest philosophical difference. Deno requires explicit permission flags to access the network, filesystem, or environment variables. deno run server.ts won't access disk unless you pass --allow-read. This is genuinely safer for running untrusted code, like a script someone sent you. Bun trusts your code by default, the same as Node. For your own apps the security model rarely matters; for third-party scripts it does.

npm compatibility maturity. Both support npm now. Bun has had npm-native compatibility from day one and handles most edge cases. Deno 2's npm support is solid but newer, and some packages still hit compatibility issues. If you're depending on a finicky npm package with native modules, Bun is more likely to work without fuss.

Web standards adoption. Deno wins here. The runtime APIs ARE web standards: fetch, FormData, URL, WebSocket, ReadableStream, Web Crypto. Code you write for Deno often runs in browsers and Cloudflare Workers with no changes. Bun implements web standards too but with more Node-flavored polyfills mixed in.

Tooling unification. Both ship as single binaries with built-in TypeScript, test runners, bundlers, and formatters. Bun's formatter is fast but young; Deno's formatter (basically dprint) is mature. Both have task runners. Deno's permissions integrate with the runtime; Bun's tooling assumes trusted code.

Hosting and edge runtimes. Bun and Deno both run on most modern platforms. Deno has Deno Deploy, a first-party edge runtime that's basically Cloudflare Workers but Deno-flavored. Bun runs anywhere a Linux binary runs. For serverless specifically, Deno Deploy is more mature than Bun's serverless story.

When to Choose Bun

• You're migrating from Node and want minimal friction
• You need every existing npm package to work
• Speed and toolchain unification matter most
• You're building with Elysia or other Bun-native frameworks
• You want one binary that does everything

When to Choose Deno

• Security model matters (running untrusted scripts, multi-tenant code)
• You're writing code that should also run in browsers or Workers
• You want JSR's typed module registry over npm
• You're deploying to Deno Deploy or Supabase Edge Functions
• Web standards alignment matters for portability

The Verdict

Both are good in 2026 and the gap between them keeps shrinking. The choice often comes down to what you care about more: performance and Node compatibility, or web standards and security.

For solo devs migrating from Node and wanting the fastest path to working code, Bun is the easier transition. Your existing knowledge transfers almost completely. Your packages mostly just work. The toolchain is unified and the speed is real.

For solo devs starting fresh, especially if you want code that's portable across runtimes (Workers, browsers, Deno Deploy), Deno has the better foundation. Writing to web standards once and running everywhere is genuinely useful, and Deno 2 made the npm friction mostly disappear.

If you're undecided, default to Bun for backend APIs and CLI tools where performance matters and you want Node-style ecosystem access. Default to Deno when you're writing code that should run in multiple environments or when you're building security-sensitive scripts. Both runtimes are far enough along that you won't regret either choice.