Hello Codeforces!

Today I want to share my project Copeforces, a problem solving toolkit I made for competitive programmers.

I built it to make common competitive programming workflows faster, cleaner, and easier to visualize while practicing, upsolving, or debugging ideas.

You can try it here:

• copeforces.netlify.app

What is Copeforces?

Copeforces is a web-based toolkit for competitive programming. It brings many small but useful utilities into one place, so I do not need to keep switching between notes, scratch files, calculators, visualizers, and reference pages.

It is designed especially for:

• Practicing algorithms
• Upsolving problems
• Debugging ideas
• Testing generated cases
• Visualizing graph/tree/search/DP concepts
• Quickly checking common formulas, limits, and implementation references

Main Features

• Contest Utilities: calculators, base converter, binary tools, ASCII/character tables, overflow checker, float precision tester, big integer calculator, expression evaluator, and more.
• Debug Tools: helpers for comparing output, checking frequencies, and debugging common mistakes.
• Test Generator: random arrays, strings, trees, graphs, queries, matrices, and custom constraints.
• String Algorithms: prefix function, Z-function, hashing, palindrome tools, and pattern matching helpers.
• Number Theory: gcd/lcm, modular arithmetic, prime tools, sieve, factorization, divisors, and related utilities.
• Matrix and Grid Tools: rotation, transpose, prefix matrix, matrix multiplication, matrix exponentiation, flood fill, grid BFS/DFS, and spiral traversal.
• Search Visualizers: binary search, lower/upper bound, answer-space binary search, ternary search, and step-by-step traces.
• Trees and Graphs: graph/tree input, traversal visualization, node stats, LCA, diameter, BFS/DFS, and drawing/analysis support.
• Dynamic Programming: knapsack, LCS, coin change, LIS, and visual DP tables.
• Greedy Tools: activity selection, fractional knapsack, job sequencing, and other greedy helpers.
• Quick Reference: complexity tables, STL complexity, math formulas, geometry formulas, bit tricks, mod values, EPS values, limits, and integer ranges.

Built-in Drawing Board

One of the most useful parts is the right-side drawing board powered by Excalidraw.
You can keep notes, draw graphs, sketch ideas, and reason visually while using the tools on the left side.

This is helpful when solving graph, tree, geometry, DP, or constructive problems where drawing the idea makes the solution much clearer.

Dark Mode / Light Mode

If you want to switch between dark mode and light mode, just click on the logo icon at the top-left corner of the page.

Why I Think It Is Useful

Competitive programming often needs many tiny tools. Usually we open several tabs or write quick scripts again and again. Copeforces tries to keep those things together in one clean interface.

It is not meant to replace thinking or implementation practice. Instead, it is a companion tool for learning, debugging, visualizing, and checking ideas faster.

Links

• https://copeforces.netlify.app

I made Copeforces for my own competitive programming workflow, and I hope it helps others too.

If you try it, feedback and suggestions are very welcome.
Hope it helps some of you during practice and upsolving!