# rust-no-std

A skill that walks your agent through no_std Rust: the core/alloc/std boundary, global allocators, panic handlers and host-side testing.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 474 installs · ★ 267
- Author: mohitmishra786
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/rust/rust-no-std/SKILL.md
- Updated: 2026-06-27
- HTML: https://affpapa.org/en/nevibecode/skills/rust-no-std

## What it does

The skill guides an agent through `#![no_std]` code — library crates for embedded and bare-metal targets that cannot link against `std`. It lays out what `core` offers without an OS or heap, how `alloc` differs, and how to opt into `Vec`, `String` and `Box` behind an `alloc` feature.

Inside you get crate structure examples, a comparison table of `core` vs `alloc` vs `std`, a global allocator built on `linked-list-allocator`, and several `#[panic_handler]` options: a spin loop, `defmt` with `cortex_m::asm::udf`, or ready-made crates such as `panic-halt` and `panic-probe`. Testing has its own section — `#![cfg_attr(not(test), no_std)]` keeps `std` available only in test mode, while `cargo check --target thumbv7em-none-eabihf` verifies compliance without hardware. For flashing with probe-rs and defmt logging the skill points to `skills/embedded/embedded-rust`, and for cross-compilation target setup to `skills/rust/rust-cross`.

Scope is the catch: the full embedded workflow and target configuration live in other skills, so an RTIC or probe-rs project needs them alongside this one. Tests on the embedded target itself won't run either — bare metal has no test runner, and the author suggests defmt-test or probe-run instead.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill rust-no-std -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/rust-no-std/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/rust-no-std/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill rust-no-std -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/rust-no-std/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill rust-no-std -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/rust-no-std/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install mohitmishra786/low-level-dev-skills rust-no-std
```

2. **Manually: put the files in place**
- File: `.github/skills/rust-no-std/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill rust-no-std -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/mohitmishra786/low-level-dev-skills --path skills/rust/rust-no-std
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/rust-no-std/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill rust-no-std -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/rust/rust-no-std/SKILL.md

## When to use it
- write a parser crate that works without std
- use Vec and String in no_std via the alloc feature
- pick a global allocator for an embedded target
- choose a panic handler for debugging or production
- run no_std crate tests on the host machine

## Example prompts
- help me write a no_std crate that parses bytes with borrowed slices
- how do I use Vec in no_std and which allocator should I add
- set up host testing for my no_std crate with cfg_attr

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: dc662ddf69960335.

BEGIN THIRD-PARTY FILE dc662ddf69960335
````text
---
name: rust-no-std
description: "Guide no_std Rust development for embedded and bare-metal targets. Use when writing #![no_std] crates, understanding core vs alloc vs std, implementing custom global allocators, selecting panic handlers for embedded, or testing no_std crates on the host without hardware."
user-invocable: true
triggers:
  - write a no_std Rust crate
  - use Vec or String without std in Rust
  - implement a global allocator in Rust
  - handle panics in no_std embedded Rust
  - test a no_std crate on the host
  - set up no_std with the alloc feature
  - difference between core alloc and std in Rust
---

# Rust no_std

## Purpose

Guide agents through `#![no_std]` Rust development: what `core` and `alloc` provide vs `std`, implementing custom global allocators, panic handler selection for embedded targets, and strategies for testing `no_std` crates on the host machine.

## When to Use

Use this skill when writing or debugging `#![no_std]` Rust code — library crates for embedded targets, or bare-metal firmware that cannot link against `std`. For the full embedded development workflow (probe-rs flashing, defmt logging, RTIC), use `skills/embedded/embedded-rust`. For cross-compilation target setup, use `skills/rust/rust-cross`. This skill focuses specifically on the `no_std` / `core` / `alloc` boundary and panic handler selection.

## Examples

- "I need a parser crate that works without std" → structure with `#![no_std]`, feature-gate alloc APIs, use borrowed slices for core API
- "How do I use Vec in a no_std environment?" → add `alloc` feature, provide a global allocator (e.g., `linked-list-allocator`), use `alloc::vec::Vec`
- "How do I test my no_std crate on my laptop?" → use `#![cfg_attr(not(test), no_std)]` to allow std in test mode, or `cargo test --target x86_64-unknown-linux-gnu`

## Workflow

### 1. no_std crate structure

```rust
// src/lib.rs
#![no_std]

// core is always available (no OS needed)
use core::fmt;
use core::mem;
use core::slice;

// alloc: heap collections — requires a global allocator
#[cfg(feature = "alloc")]
extern crate alloc;
#[cfg(feature = "alloc")]
use alloc::{vec::Vec, string::String, boxed::Box, format};

pub fn add(a: u32, b: u32) -> u32 {
    a + b
}
```

```toml
# Cargo.toml
[features]
default = []
alloc = []       # opt-in to heap allocation

[dependencies]
# no_std-compatible dependencies only
```

### 2. core vs alloc vs std
````
END THIRD-PARTY FILE dc662ddf69960335

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