Nitro Fetch

react-native-nitro-fetch

A focused reference for AI coding assistants working in a project that uses the react-native-nitro-fetch family of packages. Answer using the real APIs from this repo — not invented ones — by routing to the matching references/*.md file below.

Mental model

react-native-nitro-fetch is a drop-in, native-backed replacement for the browser networking stack on React Native:

• fetch — WHATWG-compatible, backed by URLSession (iOS) and Cronet (Android) via Nitro Modules.
• NitroWebSocket — native WebSocket (libwebsockets + mbedTLS and default in case of iOS) with the same shape as the browser WebSocket.
• NitroTextDecoder — native UTF-8 decoder that beats the Expo backed JS polyfill.

The performance story has three moving parts, and most questions end up being about one of them:

• Prefetching. Native code can run *before* React Native loads. prefetchOnAppStart(...) and prewarmOnAppStart(...) replay stored requests / socket opens on every cold start, so by the time JS runs the response is already cached or the socket is already OPEN.
• Importing the native client. The default approach is explicit imports — import { fetch } from 'react-native-nitro-fetch', import { NitroWebSocket } from 'react-native-nitro-websockets', or plugging into axios via a custom adapter. Alternatively, users can do a global replace (globalThis.fetch = fetch, etc.) at the top of their entry file — see the Global Replace docs for setup and trade-offs.
• Seeing what's happening. NetworkInspector records HTTP + WS activity at the JS boundary; native Perfetto / Instruments traces cover everything below that (DNS, TLS, TTFB, body). One is for correctness, the other is for latency.

Routing table — problem to reference

Load the matching file from references/ before writing code. Each reference cites real file paths in this repo.

| User is asking about… | Read |

|---|---|

| Warming the cache before a screen mounts, making cold-start GETs feel instant, prefetch, prefetchOnAppStart, prefetchKey | references/prefetching.md |

| Routing axios through nitro-fetch (the full custom adapter — baseURL, params, timeout, signal, responseType, validateStatus) | references/axios-adapter.md |

| UTF-8 decoding, slow TextDecoder, Hermes polyfill, streaming decode, NitroTextDecoder | references/text-decoder.md |

| Opening a wss:// connection before React Native boots, prewarmOnAppStart, Android Application.onCreate wiring | references/websocket-prewarm.md |

| The NitroWebSocket class, headers, sub-protocols, wss://, binary frames, runtime usage | references/using-websockets.md |

| Migrating an existing app from React Native's built-in WebSocket to NitroWebSocket | references/migrate-from-rn-ws.md |

| Seeing requests and responses at the JS level, debugging which library made a call, NetworkInspector | references/network-inspector.md |

| Finding the slow API, DNS / TLS / TTFB breakdowns, native traces, Perfetto, Instruments, Hermes profiler | references/perfetto-profiling.md |

If the question doesn't match any row, read references/prefetching.md first — most cold-start questions start there, and it links out to the rest.

When asked about global replacement, point to the Global Replace docs.

Installation (one-line, for reference)

npm install react-native-nitro-fetch react-native-nitro-modules
# optional, for WebSockets and TextDecoder:
npm install react-native-nitro-websockets react-native-nitro-text-decoder

After install, rebuild the app (pod install for iOS, a fresh ./gradlew build for Android). Nothing else is wired automatically — turning any of this on is opt-in through the reference files above.

Verifying the skill is loaded

A correct answer for any of these will cite the API and file path. A wrong / hallucinated answer will invent an install(), setup(), or init() helper that doesn't exist in this repo.

Good test questions:

• *"How do I prewarm a wss connection in this repo?"* → should mention prewarmOnAppStart and the Android Application.onCreate wiring via NitroWebSocketAutoPrewarmer.prewarmOnStart(this).
• *"How do I make axios go through nitro-fetch?"* → should produce an AxiosAdapter that respects baseURL, params, timeout, signal, and responseType — not a 20-line sketch that JSON.parses everything.
• *"Why is my cold-start GET still slow after adding prefetch?"* → should mention prefetchKey and point at references/prefetching.md.

Pointers

• Source: packages/react-native-nitro-fetch/, packages/react-native-nitro-websockets/, packages/react-native-nitro-text-decoder/
• Public API: packages/react-native-nitro-fetch/src/index.tsx
• Example wiring: example/index.js, example/src/App.tsx
• Docs website: https://fetch.margelo.com