mojo
Expert guidance for Mojo, the programming language by Modular that combines Python's usability with C-level performance. Helps developers write high-performance AI/ML code, optimize numerical computations with SIMD and parallelism, and gradually port Python code to Mojo for orders-of-magnitude speedups.
Usage
Getting Started
- Install the skill using the command above
- Open your AI coding agent (Claude Code, Codex, Gemini CLI, or Cursor)
- Reference the skill in your prompt
- The AI will use the skill's capabilities automatically
Example Prompts
- "Review the open pull requests and summarize what needs attention"
- "Generate a changelog from the last 20 commits on the main branch"
Documentation
Overview
Mojo, the programming language by Modular that combines Python's usability with C-level performance. Helps developers write high-performance AI/ML code, optimize numerical computations with SIMD and parallelism, and gradually port Python code to Mojo for orders-of-magnitude speedups.
Instructions
Python Compatibility
# Mojo can run Python code directly and call Python libraries.
# Start with Python, optimize hot paths in Mojo.
from python import Python
fn main() raises:
# Import any Python library
let np = Python.import_module("numpy")
let plt = Python.import_module("matplotlib.pyplot")
# Use NumPy arrays as usual
let data = np.random.randn(1000)
let mean = np.mean(data)
let std = np.std(data)
print("Mean:", mean, "Std:", std)
# Plot with matplotlib
plt.hist(data, bins=30)
plt.title("Distribution")
plt.savefig("plot.png")
High-Performance Structs
# matrix.mojo — Custom matrix type with SIMD operations
# This runs 10-100x faster than equivalent NumPy for small matrices.
from math import sqrt
from algorithm import vectorize, parallelize
struct Matrix:
var data: DTypePointer[DType.float64]
var rows: Int
var cols: Int
fn __init__(inout self, rows: Int, cols: Int):
self.rows = rows
self.cols = cols
self.data = DTypePointer[DType.float64].alloc(rows * cols)
memset_zero(self.data, rows * cols)
fn __getitem__(self, row: Int, col: Int) -> Float64:
return self.data.load(row * self.cols + col)
fn __setitem__(inout self, row: Int, col: Int, val: Float64):
self.data.store(row * self.cols + col, val)
fn __del__(owned self):
self.data.free()
fn matmul(self, other: Matrix) -> Matrix:
"""Matrix multiplication using SIMD vectorization.
Processes multiple floating-point operations per CPU instruction.
On a modern CPU with 256-bit SIMD, this processes 4 float64 ops
at once — a 4x speedup over scalar code.
"""
var result = Matrix(self.rows, other.cols)
let simd_width = simdwidthof[DType.float64]()
@parameter
fn calc_row(row: Int):
for k in range(self.cols):
@parameter
fn dot[simd_width: Int](col: Int):
result.data.store[width=simd_width](
row * other.cols + col,
result.data.load[width=simd_width](row * other.cols + col)
+ self[row, k] * other.data.load[width=simd_width](k * other.cols + col)
)
vectorize[dot, simd_width](other.cols)
parallelize[calc_row](self.rows) # Parallelize across CPU cores
return result
fn frobenius_norm(self) -> Float64:
"""Compute the Frobenius norm using SIMD reduction."""
var sum: Float64 = 0.0
let simd_width = simdwidthof[DType.float64]()
@parameter
fn accumulate[width: Int](idx: Int):
let vals = self.data.load[width=width](idx)
sum += (vals * vals).reduce_add()
vectorize[accumulate, simd_width](self.rows * self.cols)
return sqrt(sum)
SIMD and Vectorization
# simd_example.mojo — Process data in parallel lanes
from algorithm import vectorize
from sys.info import simdwidthof
fn relu_activation(inout data: DTypePointer[DType.float32], size: Int):
"""Apply ReLU activation using SIMD.
Processes 8 float32 values simultaneously on AVX2 CPUs,
or 16 on AVX-512. The @parameter decorator ensures the
SIMD width is resolved at compile time.
"""
let simd_width = simdwidthof[DType.float32]() # 8 on AVX2
@parameter
fn apply_relu[width: Int](idx: Int):
let values = data.load[width=width](idx)
let zeros = SIMD[DType.float32, width](0)
data.store[width=width](idx, values.max(zeros))
vectorize[apply_relu, simd_width](size)
fn softmax(inout data: DTypePointer[DType.float32], size: Int):
"""Numerically stable softmax with SIMD operations."""
# Find max for numerical stability
var max_val: Float32 = data.load(0)
for i in range(1, size):
let val = data.load(i)
if val > max_val:
max_val = val
# Compute exp(x - max) and sum
var sum: Float32 = 0.0
for i in range(size):
let exp_val = math.exp(data.load(i) - max_val)
data.store(i, exp_val)
sum += exp_val
# Normalize
let inv_sum = 1.0 / sum
let simd_width = simdwidthof[DType.float32]()
@parameter
fn normalize[width: Int](idx: Int):
data.store[width=width](idx, data.load[width=width](idx) * inv_sum)
vectorize[normalize, simd_width](size)
Parallelism
# parallel.mojo — Multi-core parallel processing
from algorithm import parallelize, vectorize
from time import now
fn parallel_image_processing(
inout pixels: DTypePointer[DType.uint8],
width: Int,
height: Int,
):
"""Apply grayscale conversion in parallel across CPU cores.
Each row is processed by a different core, and within each row,
SIMD processes multiple pixels simultaneously.
"""
@parameter
fn process_row(row: Int):
let row_offset = row * width * 3 # 3 channels (RGB)
for col in range(width):
let idx = row_offset + col * 3
let r = pixels.load(idx).cast[DType.float32]()
let g = pixels.load(idx + 1).cast[DType.float32]()
let b = pixels.load(idx + 2).cast[DType.float32]()
# Luminance formula: 0.299R + 0.587G + 0.114B
let gray = (0.299 * r + 0.587 * g + 0.114 * b).cast[DType.uint8]()
pixels.store(idx, gray)
pixels.store(idx + 1, gray)
pixels.store(idx + 2, gray)
parallelize[process_row](height) # Each core handles a subset of rows
Installation
# Install Modular CLI
curl -s https://get.modular.com | sh -
# Install Mojo
modular install mojo
# Verify
mojo --version
# Run a Mojo file
mojo run my_program.mojo
# Build a binary
mojo build my_program.mojo -o my_program
Examples
Example 1: Building a feature with Mojo
User request:
Add a real-time collaborative python compatibility to my React app using Mojo.
The agent installs the package, creates the component with proper Mojo initialization, implements the python compatibility with event handling and state management, and adds TypeScript types for the integration.
Example 2: Migrating an existing feature to Mojo
User request:
I have a basic high-performance structs built with custom code. Migrate it to use Mojo for better high-performance structs support.
The agent reads the existing implementation, maps the custom logic to Mojo's API, rewrites the components using Mojo's primitives, preserves existing behavior, and adds features only possible with Mojo (like SIMD and Vectorization, Parallelism).
Guidelines
- Start with Python, optimize in Mojo — Use Python imports for prototyping; rewrite hot loops in native Mojo for 10-1000x speedups
- Use SIMD for data processing —
vectorizeprocesses multiple values per instruction; always prefer it over scalar loops for numeric data - Parallelize across cores —
parallelizedistributes work across CPU cores; combine withvectorizefor maximum throughput fnoverdef— Usefnfor performance-critical functions (strict typing, no overhead); usedeffor flexibility- Owned and borrowed references — Use
borrowed(default) for read-only,inoutfor mutation,ownedfor transfers; this enables zero-copy optimizations - Compile-time metaprogramming — Use
@parameterfor compile-time evaluation; SIMD widths, loop unrolling, and specialization happen at compile time - Profile before optimizing — Use
mojo build -O3and benchmark; not everything needs SIMD — focus on actual bottlenecks - Gradual migration — Port one function at a time from Python to Mojo; the interop layer makes incremental adoption easy
Information
- Version
- 1.0.0
- Author
- terminal-skills
- Category
- Development
- License
- Apache-2.0