AtCoder vs Codility

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.

Codility offers Screen, Interview and Skills Intelligence for engineering hiring, technical interviews and workforce skills mapping. Screen provides online technical assessments with objective scores and detailed breakdowns across a library of more than 1,300 tasks. Interview supports live technical interviews in a VS Code environment, including whiteboarding, pair programming, live code execution, recordings and structured evaluation. Skills Intelligence maps engineering capabilities, identifies gaps and supports project staffing and development planning. Teams can configure AI use for each assessment, with tasks on prompt engineering, evaluating AI-generated code and working with AI tools. Codility connects with recruiting and HR systems including Greenhouse, Lever, Ashby, Workday, SAP and SmartRecruiters. Its public API supports invitations, result retrieval, completion alerts and custom reporting, with a limit of 500 requests per user per hour. Codility says its security program is ISO 27001 certified and covered by a SOC 2 Type II report; it also states that data is encrypted in transit and at rest. It states GDPR and CCPA compliance and WCAG 2.2 AA accessibility. The company was founded in 2009 and is headquartered in London.