Lyn

Lyn is a lightweight Backend TypeScript framework with Bun.

What and Why Lyn?

Lyn is:

• Fast
• Type-safe
• Secure with built-in authentication
• Runs everywhere

Lyn isn't here to replace existing frameworks. It was born from the need for a simple way to build things faster, with the best quality and developer experience.

Most frameworks serve as a foundation for your products. However, I often need something simpler with authentication and security built-in by default.

That's why Lyn focuses on being the easiest tool for POCs, solopreneurs, and agencies.

Lyn leverages Bun and the best JavaScript libraries for the job.

Code example

Code:

new Lyn()
  .get("/text", () => {
    return "Hello World";
  })
  .get("/json", () => {
    return {
      message: "Hello World",
    };
  })
  .get(
    "/:name",
    ({ params }) => {
      return {
        message: "Hello " + params.name,
      };
    },
    {
      params: z.object({
        name: z.string(),
      }),
    }
  )
  .get(
    "/test",
    ({ query }) => {
      return {
        message: `Hello ${query.name} ${
          query.isAdmin ? "is admin" : "is not admin"
        } and you are ${query.age} years old`,
      };
    },
    {
      query: z.object({
        name: z.string(),
        isAdmin: z.boolean(),
        age: z.number(),
      }),
    }
  )
  .post("/", ({ set }) => {
    set.status = 201;
    return {
      message: "Hello World",
    };
  })
  .post(
    "/users",
    ({ body, set }) => {
      set.status = 201;
      return {
        message: "Hello " + body.name,
      };
    },
    {
      body: z.object({
        name: z.string(),
      }),
    }
  )
  .listen(3000);

Run it (Bun >= 1.3.6, NODE_ENV is required):

bun install
NODE_ENV=development bun run dev

Documentation

• Getting started
• Routing
• Validation
• Responses & errors
• Configuration — env variables, logging
• Testing

Contributing with an AI agent? See CLAUDE.md (also available as AGENTS.md).

Roadmap:

• Register Routes
• Request lifecycle
• Body validation
• Params validation
• Query validation
• Add a logger
• Environment variables
• Example Project
• Auth
• Documentation
• Publish
• Do a Security Checklist

Contact

X @RouretLucas

License

MIT