AtCoder vs Eolymp

AtCoder is a free web service for competitive programming contests and practice. Users solve programming problems in Algorithm Contest and Heuristic Contest formats, and can run source code in a browser rather than setting up a local programming environment. Its practice library contains about 5,000 past problems with explanations, and it supports nearly all major programming languages, including C++, Python, Rust, Java, and C#. Beginner Contests take place weekly, Regular Contests about monthly, Grand Contests five to six times a year, and heuristic contests about monthly. Real-time participation in Algorithm or Heuristic contests changes a user's AtCoder rating. AtCoder Jobs lets users apply to companies using their rating for roles including internships and experienced positions. PAST is an online algorithm skills test available in Japanese and English, with problems updated every six months. AtCoder says it has about 200,000 registered users and about 10,000 participants in real-time contests weekly. Its terms limit members to one account and prohibit account sharing, lending, or transfer.

Eolymp provides tools for creating and hosting programming competitions and learning activities, from small practice rounds to official contests the maker says can involve thousands of participants. Organizers can run synchronized online contests or virtual contests with individual timers, then allow upsolving. Contests support IOI scoring with partial credit and ICPC scoring with time penalties. Problem-authoring tools cover statements, tests, checkers, solutions, validators, interactors and generators; problems can also be imported from Basecamp or Polygon. Courses bring together modules, learning materials, assignments and grades. The API uses HTTPS and JSON, offers API-key or OAuth 2.0 authentication, and has SDKs for Python, Go, PHP and JavaScript. Each space can connect supported AI clients through an MCP server, subject to the signed-in user's permissions. Free Services cost nothing and include problem materials, competition access and automatic solution testing. A new space can be tried free for 30 days with five seats and no payment details to start.