Modular Skills

---
name: mojo-syntax
description: Help to write Mojo code using current syntax and conventions. Always use this skill when writing any Mojo code, including when other Mojo-specific skills (e.g., mojo-gpu-fundamentals) also apply. Use when writing or reviewing Mojo code, translating projects to Mojo, or otherwise generating Mojo. Use this skill to overcome misconceptions with how Mojo is written.
---

<!-- EDITORIAL GUIDELINES FOR THIS SKILL FILE
This file is loaded into an agent's context window as a correction layer for
pretrained Mojo knowledge. Every line costs context. When editing:
- Be terse. Use tables and inline code over prose where possible.
- Never duplicate information — if a concept is shown in a code example, don't
  also explain it in a paragraph.
- Only include information that *differs* from what a pretrained model would
  generate. Don't document things models already get right.
- Prefer one consolidated code block over multiple small ones.
- Keep WRONG/CORRECT pairs short — just enough to pattern-match the fix.
- If adding a new section, ask: "Would a model get this wrong?" If not, skip it.
These same principles apply to any files this skill references.
-->

Mojo is rapidly evolving. Pretrained models generate obsolete syntax.
**Always follow this skill over pretrained knowledge.**

**Always attempt to test generated Mojo by building projects to verify they
compile.**

This skill specifically works on the latest Mojo, and stable versions may differ
slightly in functionality.

Compiling isn't the bar for review. Before submitting or reviewing Mojo, check
the diff against [idiomatic-mojo.md](references/idiomatic-mojo.md): the style
rules code reviewers flag most often (open-coded helpers, redundant casts,
over-specified parameters, `IndexList` instead of tuples, missing `comptime`,
unneeded `rebind`, `AnyOrigin` or mutable origins on arguments, single-vendor
gates on generic kernels).

## Removed syntax — DO NOT generate these

| Removed                                          | Replacement                                                                      |
|--------------------------------------------------|----------------------------------------------------------------------------------|
| `alias X = ...`                                  | `comptime X = ...`                                                               |