architecture

An agent guide for the design and API structure of React Native Testing Library, a tool for testing mobile components as users would use them. It documents the library's TypeScript, React Native, and Jest codebase.

In plain words
What is it for?
Designing or reviewing library APIs, working on rendering and cleanup behavior, and contributing to the React Native Testing Library codebase.
Why use it?
It helps contributors understand the library's core principles, runtime, entry points, and public API before changing its implementation.

Agent

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/callstack/react-native-testing-library/architecture
Clone the repo
git clone --depth 1 https://github.com/callstack/react-native-testing-library
Per session 0 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 179 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00000 $0.00179
Opus 5 $0.00000 $0.00089
Sonnet 5 $0.00000 $0.00036
Haiku 4.5 $0.00000 $0.00018

Measured yesterday against content hash 66bc6f8c8bb8, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

architecture scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

agents/architecture.md · 22 lines

What it actually says

Architecture And API Design

Project overview

@testing-library/react-native provides utilities for testing React Native components in ways that resemble real usage and avoid implementation details.

  • Tech stack: TypeScript, React Native, Jest
  • Core principle: the closer tests are to real usage, the more confidence they provide
  • Runtime model: the library simulates the React Native runtime on top of test-renderer

API design principles

  • Prefer a small public API surface.
  • Expose underlying React and react-reconciler capabilities when Testing Libraries need them.
  • Render host elements only.
  • Provide escape hatches to fibers when needed.

Key entry points

  • src/pure.ts: side-effect-free core logic without auto-cleanup
  • src/index.ts: main entry point that re-exports pure and adds auto-cleanup side effects
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 22 lines · 0 tokens per session scan A 66bc6f8c8bb8

Subscribe to this mod's changes

architecture is an agent published in the GitHub repository callstack/react-native-testing-library (3,414 stars, last pushed 19d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 179 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.