Useful tools.
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Practical calculators, visualizers, simulators, and developer utilities. No ads, no signups, no paywalls.
3-Way & 4-Way Switch Circuit Wiring Interactive Simulator
Interactive educational circuit simulator demonstrating how 3-way and 4-way switches, traveler conductors, and common terminals operate in simplified AC circuits.
cURL to Playwright API & Grafana k6 Script Converter
Convert cURL commands directly into clean Playwright APIRequestContext tests, Grafana k6 load test scripts, and route mock interceptors with automatic noise stripping and secret masking.
Stair Stringer Calculator & 2D Framing Visualizer
Calculate exact stair risers, tread runs, stringer cut angles, 2x12 lumber stock, and bottom riser tread thickness deductions with IRC and IBC code compliance checks.
Peptide Reconstitution & Syringe Dosage Visualizer
Calculate exact insulin syringe units (U-100, U-50, U-30) for peptide reconstitution (Tirzepatide, Semaglutide, BPC-157). Features an interactive SVG syringe with animated plunger and tick-mark zoom.
4×6 Thermal Shipping Label Auto-Cropper & PDF Rotator
Free 100% client-side tool to crop full-sheet 8.5×11 shipping labels to 4×6 direct thermal format for Rollo, Zebra, Munbyn, and Dymo 4XL printers. Zero server uploads.
CAT Scale Trailer Tongue Weight & WDH Restoral Calculator
Calculate exact trailer tongue weight, gross trailer weight, and SAE J2807 Front Axle Load Restoral (FALR) from CAT Scale 2-pass and 3-pass tickets. Includes sway risk meter and payload checks.
California Final Paycheck Waiting Time Penalty Calculator (§ 203)
Calculate California Labor Code § 203 waiting time penalties, daily wage rates, unpaid accrued PTO, and statutory interest for late final paychecks. Generates an instant formal legal demand letter.
Audio Delay, Reverb & LFO Tempo Synchronizer Studio
Calculate exact milliseconds (ms), LFO frequencies (Hz), sample-accurate DAW buffer offsets, and tempo-synced reverb decay times for any BPM. Features live Web Audio API auditioning and tap tempo.
Picture Frame Mat Board Border & Optical Weighting Studio
Calculate exact mat board border widths, window opening cut dimensions, and optical bottom-weighting for custom picture frames. Features real-time SVG visualizer, double accent mat reveals, and Logan bevel mat cutter pencil marking guides.
Camper Van & RV Solar/Battery System Architect
Size rooftop solar panels, LiFePO4 lithium battery banks, MPPT charge controllers, and pure sine inverters with real-time power flow simulation and ABYC wire gauge safety.
Home EV Charger & Electrical Panel Load Calculator (NEC 220)
Calculate residential service panel capacity for Level 2 EV charging under NEC Article 220.82. Verify 100A, 150A, or 200A panel headroom, test smart splitter EVEMS bypasses, and generate 1-click permit worksheets.
Free Unlimited BRRRR Strategy Investment Deal Analyzer
Analyze Buy, Rehab, Rent, Refinance, Repeat (BRRRR) deals with zero signup or paywalls. Model hard money holding costs, cash-out refi proceeds, capital velocity, Infinite Return badges, and DSCR lender qualification with 1-click printable bank sheets.
Browse by Category
Explore specialized tools and calculators organized by technical discipline
Home Trades & Electrical
Interactive circuit simulators, wiring diagrams, and construction tools.
Developer & DevOps
Code translators, schema inferencers, and API test generators.
Shipping & E-Commerce
Thermal label croppers, barcode generators, and marketplace fee calculators.
Audio & Acoustics
Delay tempo synchronizers, room mode heatmaps, and synth simulators.
Optics & Photography
Multi-crop aspect ratio visualizers and star trailing simulators.
Automotive & Towing
Trailer sway physics engines, tongue weight meters, and EV energy tools.
Legal & Employment
FLSA overtime calculators, severance estimators, and labor compliance tools.
Health & Nutrition
Peptide reconstitution syringe calculators, macro splitters, and fasting trackers.
Real Estate & Finance
BRRRR strategy deal analyzers, DSCR commercial loan qualifiers, and capital velocity models.