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Every tool runs in your browser.
Fast, free utilities for developers, DevOps engineers and electrical engineers — QR codes, JWTs and hashes alongside cron, CIDR, Ohm’s law and resistor codes. No accounts, no uploads, no waiting: nothing you type or drop here leaves this page.
Why it matters
Most everyday engineering tasks — decoding a token, checking a resistor value, sizing a trace — take about fifteen seconds of actual work. Finding a tool that does them without a sign-up wall, an interstitial, or a paste box that quietly uploads your data takes considerably longer.
KitBoxDev is the answer to that: open the page, do the thing, close the tab. The client-side-only constraint is the whole design, not a feature.
Cryptographic work uses the browser’s own Web Crypto API rather than a bundled implementation, and the whole site keeps working offline once loaded.
You can paste a production JWT, an authenticator secret, or a customer’s data into a tool here without that being a security incident — because there is no server for it to reach.
The catalog
35 tools, grouped by who reaches for them
Search filters every collection at once from the home page, and CtrlK opens the command palette from inside any tool. Star the ones you use and they float to the top.
Developer Tools
12Fast, free utilities for everyday developer work — QR codes, JWTs, hashes, JSON and more. No accounts, no uploads.
- 01
QR Code Generator
Turn text or URLs into crisp QR codes and download them as PNG or SVG.
Generator - 02
QR Code Reader
Decode QR codes from an image, a drag-and-drop file, or your webcam.
Decoder - 03
TOTP Generator
Turn an authenticator secret or otpauth QR code into live one-time passwords, with a 30-second countdown and one-click copy.
Generator - 04
Text Scrambler
Shuffle characters or words with a reproducible seed and adjustable intensity.
Text - 05
JWT Debugger
Decode and verify a JSON Web Token, or sign a new one — HMAC, RSA, ECDSA and Ed25519, both halves on one page.
Decoder - 06
Base64 Encode / Decode
Encode and decode Base64 for text and files, with URL-safe support.
Converter - 07
Encrypt / Decrypt Text
Encrypt and decrypt text with a passphrase (AES-GCM/CBC) or an RSA public key — output as Base64.
Crypto - 08
Hash Generator
Compute MD5, SHA-1, SHA-256, and SHA-512 digests, or Argon2 password hashes with a pepper.
Generator - 09
JSON Formatter
Pretty-print, minify, and validate JSON with precise error positions and a tree view.
Text - 10
UUID Generator
Generate one or thousands of v4 UUIDs and copy them all at once.
Generator - 11
URL Encoder / Decoder
Percent-encode or decode URLs and query-string components.
Converter - 12
Regex Tester
Test a JavaScript regular expression live — highlighted matches, capture groups, a replace preview, and a library of common patterns.
Text
DevOps Tools
10Fast, free utilities for everyday operations work — cron expressions, CIDR maths, YAML, permissions and certificates. Everything runs in your browser.
- 01
Cron Expression Parser
Read a cron line in plain English, expand every field, and see the next ten firings in local time and UTC.
Decoder - 02
CIDR / Subnet Calculator
Turn an IPv4 or IPv6 prefix into netmask, broadcast, usable range and host count — then split it, compare it, or aggregate a range.
Network - 03
chmod / Unix Permissions Calculator
Bind permission checkboxes, octal and symbolic modes together — including setuid, setgid, sticky and what a umask leaves behind.
Reference - 04
Uptime & SLA Calculator
Convert an availability target into allowed downtime per day, month and year, track the error budget, and chain several services together.
Calculator - 05
Kubernetes Resource Converter
Convert CPU and memory quantities between every suffix Kubernetes accepts, and catch the ones that mean a billion times what you meant.
Converter - 06
YAML ↔ JSON Converter
Convert either way with key order and comments-free fidelity, then see every scalar whose written form and parsed value disagree.
Converter - 07
.env File Converter
Parse a dotenv file the way real readers do — quoting, escapes, comments — and retype it as JSON, YAML, docker flags, Compose, a Secret or a ConfigMap.
Converter - 08
htpasswd Generator
Build Apache basic-auth lines with bcrypt, $apr1$, {SHA} or plain text, verify an existing hash, and collect several users into one file.
Generator - 09
docker run to Compose Converter
Turn a docker run command into a Compose service — with every flag either translated or listed with the reason it could not be.
Converter - 10
Certificate & CSR Decoder
Read an X.509 certificate, a chain or a signing request — subject, SANs, validity, key, extensions and fingerprints, all decoded in your browser.
Decoder
Electrical Engineering Tools
13Fast, free calculators and references for everyday electronics — Ohm’s law, resistor codes, filters, timers and more. Everything runs in your browser.
- 01
Ohm’s Law Calculator
Enter any two of voltage, current, resistance or power — the other two are solved instantly.
Calculator - 02
Voltage Divider Calculator
Solve a resistive divider for any unknown, handle a loaded output, and pick standard-value resistor pairs.
Calculator - 03
LED Series Resistor Calculator
Size the series resistor for one or more LEDs, with a safe standard value, real current and power.
Calculator - 04
555 Timer Calculator
Compute astable frequency and duty or monostable pulse width, and reverse-design resistors for a target.
Calculator - 05
PWM Duty Cycle Calculator
Convert between frequency, duty cycle, on/off times and average voltage, with a bit-depth resolution helper.
Calculator - 06
Battery Life Estimator
Estimate how long a battery lasts from its capacity, average load current and a real-world derating factor.
Calculator - 07
Resistor Color Code Calculator
Decode 4-, 5-, and 6-band resistors to a value, tolerance and tempco — or turn a value into its colour bands.
Decoder - 08
Capacitor Code Decoder
Decode a 3-digit ceramic capacitor code and tolerance letter to a value — or encode a capacitance back to its code.
Decoder - 09
Wire Gauge & Ampacity Reference
Look up AWG wire properties and ampacity, size a gauge for a target current, and estimate voltage drop over a run.
Reference - 10
RC / RL Filter Calculator
Compute time constant, cutoff frequency and step response for a first-order RC or RL filter, with preferred-value design.
Calculator - 11
Engineering Unit Converter
Convert voltage, current, power, energy, frequency, charge and more between units — including logarithmic dBm, dBW and dBV.
Converter - 12
PCB Trace Width Calculator
Size a PCB trace for a target current and temperature rise with IPC-2221, then read its resistance, voltage drop and power loss.
Calculator - 13
Logic Gate Simulator
Type a boolean expression and get its full truth table and canonical sum-of-products — AND, OR, NOT, XOR, NAND, NOR, XNOR.
Simulator
Under the hood
How it stays fast, private and honest
01 Architecture
No backend to leak
There is no server-side processing, no database and no account system. Every tool is plain client-side code, so your input has nowhere to go.
02 Cryptography
The browser’s own Web Crypto
Hashes, JWT signatures and encryption run through the platform’s Web Crypto API rather than a hand-rolled implementation bundled into the page.
03 Delivery
Prerendered, then offline
An Angular app prerendered to static HTML and served from a CDN. It keeps working offline once loaded, and installs as a progressive web app if you want it in the dock.
04 Navigation
Keyboard first
Ctrl K opens the command palette over the whole catalog from inside any tool, and / jumps straight to search on the home page.
05 Editorial
Every page cites its method
Tool pages carry the formula or specification they implement, worked examples and the caveats — IPC-2221 for trace width, RFC 6238 for TOTP, the AWG geometric definition for wire gauge. Estimates are labelled as estimates.