justapi Runtime

A production-grade Python web framework written in Rust. Rust owns the
network/protocol stack; Python executes only application logic.

10-20x faster than FastAPI — see BENCHMARKS.md.

Project Status

Phase 40 — The JustAPI 2.0 "Singularity" Release (in progress)

All 39 prior phases complete. See PLAN.md for the full roadmap.

Architecture

Kernel → epoll/io_uring → Connection Manager → tokio task
  → TLS (rustls) → HTTP parse (hyper) → Router (matchit)
  → Middleware chain (Rust: auth/CORS/rate-limit/compression)
  → Python boundary (typed, zero-copy request view via PyO3)
  → Application code (native Python handler)
  → Rust serializer (serde_json/simd-json)
  → Response write → Socket

justapi provides a single native Python API (Tier B) — the FastAPI
replacement that runs entirely in Rust with zero-copy Python integration.

Quick Start

Python Native API

from justapi import JustAPIApp

app = JustAPIApp()

@app.get("/hello/{name}")
async def hello_handler(request):
    name = request["path_params"]["name"]
    return {"message": f"Hello {name}!"}

app.run("127.0.0.1:8080")

Install the package:

pip install justapi

Or build from source with maturin:

cd crates/justapi-py
maturin develop --release

CLI

# Run server with Rust-defined routes
justapi serve --addr 127.0.0.1:8080

# Generate a client SDK from your API
justapi gen-client --lang python

Features

Development

Prerequisites

• Rust 1.85+ (edition 2021)
• Python 3.11+

Building

cargo build --workspace               # debug build
cargo build --workspace --release      # release build
cargo test --workspace                 # run all tests (236+)
cargo clippy --workspace --tests -- -D warnings # lint
cargo fmt --check                      # format check
cargo miri test -p justapi-core        # memory safety (nightly)

Benchmarking

See BENCHMARKS.md for methodology and results.

# Install load generator
cargo install oha

# Run baseline benchmarks
bash benchmarks/run_baselines.sh

Project Structure

crates/
  justapi-core/   — networking, protocol, scheduler, memory
  justapi-py/     — PyO3 bindings, native Python API
  justapi-cli/    — `justapi` CLI binary
  justapi-bench/  — internal benchmark harness
python/
  justapi/        — pip-installable Python package
fuzz/              — cargo-fuzz targets (6 targets)
docs/              — documentation
skills/            — reusable knowledge modules for development
benchmarks/        — workload scripts for performance testing

Documentation

• PLAN.md — Living roadmap and current status
• AGENTS.md — Development rules and conventions
• DECISIONS.md — Architecture decision records
• BENCHMARKS.md — Performance results ledger
• docs/security/ — Security policies and pentest guide
• docs/plugins.md — Plugin development guide

License

MIT