SeamJS

A compile-time rendering (CTR) framework: extract HTML skeletons from UI components at build time, inject server data through typed procedures at request time. Instead of blurring the server-client boundary, SeamJS re-establishes it — data fetching stays on the server as typed procedures, rendering stays on the client as UI components, and the framework bridges them through schema-driven codegen and template injection.

Status: core concepts validated with React; runtime adapters and client libraries in early development.

Design Philosophy

SeamJS is a rendering strategy, not a full-stack framework tied to specific technologies.

• UI stack: React-first for concept validation. The CTR pipeline (skeleton extraction + template injection) is UI-agnostic — adapting other frameworks (Vue, Svelte, Solid, ...) requires a corresponding skeleton extractor and client bindings. Community contributions welcome.
• API bridge: Currently uses JSON-RPC over HTTP. Not married to this approach — if a better protocol fits, open an issue or send a PR.
• Backend runtime: The server core defines a protocol, not a runtime. TypeScript and Rust implementations are provided as reference; any language can implement the seam protocol by serving the /_seam/* endpoints.

How CTR Differs

• vs SSG / SSR: SSG bakes data into HTML at build time (static); SSR renders full HTML at every request (dynamic). CTR splits the two — structure is extracted once at build time, data is injected per request. No server-side rendering runtime, no stale static pages.
• vs CSR / SSR: CSR ships an empty shell and renders everything client-side; SSR duplicates rendering logic on the server to produce HTML. CTR avoids both extremes — the server never runs UI components, it only fills typed slots in a pre-built skeleton. The client hydrates a known structure instead of reconciling server-rendered markup.

Packages

CLI

Package	Crate / npm	Description
cli/core	seam-cli	Build skeletons, generate typed clients, orchestrate dev servers
cli/pkg	@canmi/seam-cli	npm distribution wrapper for the CLI binary

Server Core

Package	Crate / npm	Description
server/core/typescript	@canmi/seam-server	Framework-agnostic server core (procedures, subscriptions, pages, HTTP layer)
server/core/rust	seam-server	Rust server core with built-in HTML template injector, built on axum
server/core/rust-macros	seam-macros	Proc macros: #[derive(SeamType)], #[seam_procedure], #[seam_subscription]

Server Adapters

Package	npm	Description
adapter/hono	@canmi/seam-adapter-hono	Hono middleware adapter
adapter/bun	@canmi/seam-adapter-bun	Standalone Bun server adapter
adapter/node	@canmi/seam-adapter-node	Node.js HTTP adapter

Client Libraries

Package	npm	Description
client/vanilla	@canmi/seam-client	Framework-agnostic client (RPC calls, SSE subscriptions)
client/react	@canmi/seam-react	React bindings (hooks, data provider, route definitions)

Template Engine

Package	npm	Description
server/injector	@canmi/seam-injector	HTML template injector (<!--seam:...--> marker replacement)

Examples

Example	Description
react-hono-tanstack	Fullstack demo: Hono server + React client with TanStack Query
server-rust	Standalone Rust backend
server-bun	Standalone Bun server
server-node	Standalone Node.js server
client-vanilla	Vanilla JS client
client-react	React client

Development

Prerequisites

• Bun — TypeScript build and test
• Cargo — Rust build and test
• Go — integration tests

Setup

bun install

Build

# TypeScript packages
bun run --filter '<pkg>' build

# Rust workspace
cargo build --workspace

Test

# TypeScript packages
bun run --filter '<pkg>' test

# Rust workspace
cargo test --workspace

# Go integration tests
cd tests/integration && go test -v
cd tests/fullstack && go test -v