mtool

mtool (multi-tool)

mtool is a Swiss army knife CLI utility written in Go, using exclusively standard library packages.

Motivation

The goal of this project was to write a practical CLI tool in Go that incorporates as many standard library modules as feasible without any third-party dependencies. Rather than contriving artificial usage, each package is pulled in naturally through a set of subcommands that solve real, everyday tasks: serving files, fetching URLs, hashing data, inspecting TLS certificates, benchmarking endpoints, converting images and more.

The result is a single-binary multi-tool that leverages 91 unique standard library packages.

Origin Story

This project started from a prompt I gave Claude. The goal was partly a fun experiment: build a useful CLI using only Go's standard library. The result ended up being far more practical than I expected. After that, I kept refining the codebase with Claude by adding more subcommands and tests as well as improving security and squashing bugs.

LLM Prompt

Write an actual *useful* program in Go that uses as many Go packages
from the standard library that you deem feasible. Make it a CLI-based
tool that can actually compile. No third-party packages are
allowed. The main goal of this exercise is to see how many standard
library packages you can shove into an actually somewhat useful
program. Do you accept this challenge?

Disclaimer

This software was developed with the assistance of AI (Anthropic Claude). It is provided "as is", without warranty of any kind, express or implied. Use at your own risk. The author assumes no liability for any damages arising from its use.

Use Cases

• Minimal / distroless Docker containers - A single static binary replaces curl, openssl, sha256sum, base64, tar, gzip, and more. A FROM scratch image with just mtool can be under 15 MB.
• CI/CD pipelines - Hash verification, archive creation, secret generation, and endpoint benchmarking without installing multiple tools or adding dependencies.
• Air-gapped / restricted environments - No package manager or network access needed. Copy one binary and get a full toolkit.
• Incident response - Drop a single binary onto a system to hash files, inspect TLS certificates, check DNS records, or fetch URLs.
• Embedded / IoT systems - Constrained environments where installing a full toolchain is impractical.
• Cross-platform developer tooling - Consistent behavior across macOS, Linux, and Windows without platform-specific alternatives.

Installation

Go Install

go install -ldflags="-s -w" github.com/jftuga/mtool/v2@latest

Homebrew

brew tap jftuga/homebrew-tap
brew update
brew install jftuga/tap/mtool

Source

git clone https://github.com/jftuga/mtool.git
cd mtool
CGO_ENABLED=0 go build -trimpath -ldflags='-s -w' -o mtool .

Requires Go 1.26 or later. No third-party dependencies.

Usage

mtool <command> [options]

Run mtool <command> -h for help on any subcommand.

Subcommands

Examples

Serve files over HTTP

mtool serve -addr :9000 -dir ./public -gzip

Serve files over HTTPS with self-signed certificate

mtool serve -addr :4443 -dir . -tls
# Access with: curl -k https://localhost:4443

Fetch a URL

mtool fetch -headers https://example.com
mtool fetch -trace https://example.com
mtool fetch -method POST -body '{"key":"val"}' -output response.json https://api.example.com

Hash files

mtool hash -algo sha256 myfile.txt
echo "hello" | mtool hash -algo md5
mtool hash -algo sha3-256 myfile.txt
mtool hash -algo sha256 -hmac "secret-key" myfile.txt
mtool hash -algo crc64 myfile.txt
mtool hash -algo adler32 myfile.txt
mtool hash -algo fnv64 myfile.txt

Encode and decode

echo "hello world" | mtool encode -format base64
echo "aGVsbG8gd29ybGQK" | mtool decode -format base64
echo "hello" | mtool encode -format base32
echo "hello" | mtool encode -format ascii85
echo "foo bar" | mtool encode -format url
echo '<div class="test">foo & bar</div>' | mtool encode -format html
echo '&lt;div&gt;foo &amp; bar&lt;/div&gt;' | mtool decode -format html
echo "Héllo wörld" | mtool encode -format qp
echo "H=C3=A9llo" | mtool decode -format qp
echo "hello" | mtool encode -format utf16 > output.utf16
mtool decode -format utf16 output.utf16

System information

mtool info
mtool info -format json
mtool info -format xml -env
mtool info -format csv

Create archives

mtool archive -format zip -output backup.zip src/ docs/ README.md
mtool archive -format tar.gz myproject/
mtool archive -format tar.zlib myproject/
mtool archive -extract backup.zip
mtool archive -extract -output ./dest archive.tar.gz
mtool archive -extract archive.tar.bz2

Generate secrets

mtool generate -mode password -length 32
mtool generate -mode password -length 16 -charset alnum
mtool generate -mode token -length 64
mtool generate -mode uuid -count 5
mtool generate -mode bigint -length 256

Benchmark an HTTP endpoint

mtool bench -n 500 -c 20 https://example.com
mtool bench -n 1000 -c 50 -method POST https://api.example.com/health
mtool bench -n 500 -c 20 -jitter 100ms https://example.com

Inspect TLS certificates

mtool inspect -mode tls google.com
mtool inspect -mode tls -port 8443 internal.example.com

Inspect DNS records

mtool inspect -mode dns github.com

Transform text

# Case conversion
echo "hello world" | mtool transform -mode upper
echo "HELLO WORLD" | mtool transform -mode lower

# Sort lines
cat names.txt | mtool transform -mode sort
cat scores.txt | mtool transform -mode sort -numeric -reverse
cat data.txt | mtool transform -mode sort -field 3 -numeric
cat mixed.txt | mtool transform -mode sort -ignore-case

# Search and replace with regex
cat log.txt | mtool transform -mode grep -pattern "ERROR|WARN"
cat messy.txt | mtool transform -mode replace -pattern "\s+" -replacement " "

# Text statistics and word frequency
cat document.txt | mtool transform -mode count
cat document.txt | mtool transform -mode freq

# Deduplicate and reverse
cat dupes.txt | mtool transform -mode uniq
echo "hello" | mtool transform -mode reverse

Convert images

mtool image photo.png photo.jpg
mtool image -quality 75 screenshot.png compressed.jpg
mtool image photo.jpg photo.gif
mtool image -format png input.gif output.png

Encrypt and decrypt files

mtool encrypt -password "my-secret" document.pdf document.pdf.enc
mtool decrypt -password "my-secret" document.pdf.enc document.pdf

# Or use an environment variable for the password
export MTOOL_PASSWORD="my-secret"
mtool encrypt document.pdf document.pdf.enc
mtool decrypt document.pdf.enc document.pdf

Compress and decompress

mtool compress -format gzip largefile.txt largefile.txt.gz
mtool compress -d -format gzip largefile.txt.gz largefile.txt
mtool compress -format zlib data.bin data.bin.zlib
mtool compress -d -format zlib data.bin.zlib data.bin
mtool compress -format lzw data.bin data.bin.lzw
mtool compress -d -format lzw data.bin.lzw data.bin
mtool compress -d -format bzip2 data.bz2 data.txt
mtool compress -level 9 -format gzip archive.tar archive.tar.gz

Note: bzip2 supports decompression only (Go's compress/bzip2 package provides a reader but no writer).

Timestamps

mtool time -mode now
mtool time -mode toepoch "2024-01-15T10:30:00Z"
mtool time -mode fromepoch 1700000000
mtool time -mode convert -zone America/New_York "2024-01-15T10:30:00Z"
mtool time -mode fromepoch -format "2006-01-02" 1700000000

JSON processing

echo '{"name":"alice","age":30}' | mtool json -mode pretty
echo '{"name":"alice","age":30}' | mtool json -mode compact
echo '{"name":"alice"}' | mtool json -mode validate
echo '{"user":{"name":"alice"}}' | mtool json -mode query -query .user.name
echo '{"items":[{"id":1},{"id":2}]}' | mtool json -mode query -query ".items[0].id"

Network utilities

mtool net -mode check localhost:8080
mtool net -mode scan -start 80 -end 443 example.com
mtool net -mode wait -timeout 30s localhost:5432
mtool net -mode echo -addr :9999

JWT decoding

mtool jwt eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0.dozjgNryP4J3jVmNHl0w5N_XgL0n3I9PlFUP0THsR8U
mtool jwt -raw <token>

Tests

Run with go test -v ./...

The test suite contains 70 test functions spread across 15 subcommand-specific files (e.g., cmd_hash_test.go, cmd_crypt_test.go). Most subcommands are tested through round-trip verification: data is processed through a command and then reversed or decoded to confirm the output matches the original input. This pattern covers encoding/decoding in all eight formats, compression/decompression across gzip, zlib, LZW, and bzip2, encryption/decryption with correct and incorrect passwords, and archive creation and extraction for tar.gz, zip, and tar.zlib. Image conversion is tested through a full PNG to JPEG to GIF to PNG chain, verifying file output at each step.

Where round-trips don't apply, tests verify correctness against known values (hash digests, epoch timestamps), check output structure (JSON pretty-printing, JWT header/payload labels, time format labels), or confirm error handling (invalid JSON, wrong password, unsupported formats, out-of-range indices). The network tests spin up local TCP listeners to exercise port checking, scanning, waiting, and echo without depending on external services. Shared test helpers for capturing stdout, writing temp files, and asserting output content live in testhelpers_test.go.

Shell Script Integration Tests

In addition to Go unit tests, the testing-harness/ directory contains 19 shell scripts that test the compiled mtool binary end-to-end. Each script exercises every flag of its subcommand, including server start/stop, stdin piping, round-trip verification, and error cases. Run them with:

go build -o mtool .
bash testing-harness/test-all.sh

Personal Project Disclosure

This program is my own original idea, conceived and developed entirely:

• On my own personal time, outside of work hours
• For my own personal benefit and use
• On my personally owned equipment
• Without using any employer resources, proprietary information, or trade secrets
• Without any connection to my employer's business, products, or services
• Independent of any duties or responsibilities of my employment

This project does not relate to my employer's actual or demonstrably anticipated research, development, or business activities. No confidential or proprietary information from any employer was used in its creation.