title: Glossary
description: Key terms and concepts used throughout the JustAPI documentation for a high-performance FastAPI alternative built in Rust.
keywords: glossary, terminology, FastAPI alternative, Rust web framework, JustAPI concepts

A

APIRouter — A class for grouping related routes into modular files. Supports the same decorators as JustAPIApp.

ASGI — Asynchronous Server Gateway Interface, the Python standard for async web servers (used by Starlette/FastAPI/Uvicorn). JustAPI is a native Rust runtime and does not implement ASGI; it runs its own pipeline for maximum throughput.

B

BackgroundTasks — Post-response task execution. Register callables to run after the HTTP response is sent.

Bulkhead — Resilience pattern that limits concurrent requests to prevent resource exhaustion.

C

Circuit Breaker — Resilience pattern that stops calling a failing service when errors exceed a threshold.

CORS — Cross-Origin Resource Sharing. HTTP mechanism for controlling cross-origin requests.

D

Depends — Dependency injection function. Resolves and injects callable results into route handlers.

Dependency Injection — Design pattern where a component's dependencies are provided externally.

G

GIL — Global Interpreter Lock. CPython's mechanism preventing multiple threads from executing Python bytecode simultaneously.

GIL Pool — Subsystem managing GIL-bound worker threads for Python handler execution.

gRPC — High-performance RPC framework using Protocol Buffers.

H

Hyper — Rust HTTP library used by JustAPI for HTTP/1.1 and HTTP/2 parsing.

J

JSON-RPC 2.0 — Lightweight remote procedure call protocol using JSON encoding.

JustAPIApp — The core application class. Register routes, middleware, plugins, and configuration.

M

matchit — Rust radix-trie router library. Provides O(1) path matching.

MCP — Model Context Protocol. Protocol for exposing tools and context to AI agents.

Middleware — Request/response processing layer that runs before and after route handlers.

N

Native Fast Path — Route execution entirely in Rust with native=True. Maximum performance (724k+ RPS).

O

OpenAPI — Standard specification for REST API documentation. JustAPI auto-generates OpenAPI 3.1 specs.

OTel — OpenTelemetry. Observability framework for distributed tracing and metrics.

P

PyO3 — Rust bindings for Python. Used to build the JustAPI Python extension module.

Pydantic — Python library for data validation. JustAPI supports Pydantic v2 models as route schemas.

R

Radix Trie — Tree data structure used by matchit for O(1) route matching.

Rustls — Rust TLS library. Provides TLS 1.2/1.3 support.

S

Schema — JustAPI's built-in validation class. Supports Field constraints and Rust-side validation.

serde_json — Rust JSON serialization library. Used for response serialization.

SSE — Server-Sent Events. HTTP protocol for server-to-client streaming.

sqlx — Rust SQL library with compile-time query checking. Powers JustAPI's database layer.

T

Tokio — Rust async runtime. Powers JustAPI's network I/O and concurrency.

Z

Zero-Copy — Data transfer technique avoiding unnecessary memory copies. Used at the Rust↔Python FFI boundary.

See Also

• ADR Index — Architecture Decision Records
• Architecture Overview — High-level design
• Rust Core Deep Dive — Runtime internals