# Free tools

Source: https://decka.dev/tools

Use browser tools to prepare activities, classroom experiments, and presentations. Each tool page includes its interactive interface and explanation.

- [Reaction Time Test](https://decka.dev/tools/reaction-time-test.md): Test your reaction time by catching a ruler that falls on screen, then read your time where you caught it. Free, no signup, and the same physics as a real ruler drop.
- [Gerrymandering Simulator](https://decka.dev/tools/gerrymandering-simulator.md): Draw five connected districts on a fixed town, count the seats your map produces, and compare it with every legal map of the same households and rules.
- [Payoff Matrix Calculator](https://decka.dev/tools/payoff-matrix-calculator.md): Edit a 2×2 payoff matrix to find pure and mixed Nash equilibria, including ties. Free, no signup. Turn your exact game into a classroom activity.
- [Repeated Prisoner’s Dilemma Simulator](https://decka.dev/tools/repeated-prisoners-dilemma-simulator.md): Compare repeated prisoner’s dilemma strategies over 1–100 rounds. Change payoffs, flip one action and inspect every score. Free, shareable and no signup.
- [Portfolio Risk Calculator](https://decka.dev/tools/portfolio-risk-calculator.md): Explore portfolio return and volatility with a free two-asset calculator. Change allocation and correlation, compare 50/50 examples, and share your assumptions.
- [Paired Period Calculator](https://decka.dev/tools/paired-period-calculator.md): Compare paired timing measurements with a free period calculator. Normalize elapsed times by cycle count, inspect sample spread, and distinguish SD from SEM.
- [Tax Incidence Calculator](https://decka.dev/tools/tax-incidence-calculator.md): Compare a per-unit tax on buyers or sellers using the same bid and ask schedules. See prices, trades and tax revenue. Free, no signup, with explicit assumptions.
- [Tier List Maker](https://decka.dev/tools/tier-list-maker.md): Paste a list, drop each item into a tier, and share the board as a link. Free, no signup, and it works with JavaScript switched off.
- [Icebreaker Questions](https://decka.dev/tools/icebreaker-questions.md): Icebreaker questions that have a concrete answer and hand the conversation back. Pick the room you are in. Free, no signup, and printable.
- [Word Cloud Generator](https://decka.dev/tools/word-cloud-generator.md): Paste any text and get a word cloud of what it actually says, with the filler words removed. Free, no signup, and you can download the picture.
- [Random Team Generator](https://decka.dev/tools/random-team-generator.md): Paste your names, pick how many teams or how many people per team, and get balanced groups instantly. Free, no signup, and you can reshuffle or print.
- [Charades Generator](https://decka.dev/tools/charades-generator.md): Get random charades words for kids, adults, movies, animals and more, at the difficulty you want. Free, no signup, and you can print the whole list.
- [Decision Wheel](https://decka.dev/tools/decision-wheel.md): Type your options, spin the wheel, get an answer. Free and no signup, with an option to remove each result so nobody is picked twice.
- [Drawing Prompt Generator](https://decka.dev/tools/drawing-prompt-generator.md): Random drawing prompts by category, graded on how hard they are to draw recognisably rather than on how obscure the word is. Free and no signup.
- [Bingo Card Generator](https://decka.dev/tools/bingo-card-generator.md): Paste a word list and get unique 3x3, 4x4 or 5x5 bingo cards, ready to print. Free, no signup, with an optional free centre square.
- [Exit Ticket Template](https://decka.dev/tools/exit-ticket-template.md): Five exit ticket formats with real prompts for seven subjects, ready to print or ask live. Free, no signup, and every question answers in one line.
- [Team Charter Template](https://decka.dev/tools/team-charter-template.md): A team charter built from questions the whole team answers, not headings one person fills in on their behalf. Free, no signup, with worked examples.