CircleCI

CircleCI is a CI/CD SaaS built by Circle Internet Services, Inc. (San Francisco; CEO Jim Rose; ~358 employees; private, $1.7B valuation, $352M raised total, last Series F $100M in 2021). Self-hosted CircleCI Server runs v4.10.0 (2026), on Nomad 1.11.3 job scheduler with MongoDB 7.0. Credits cost $0.0006 each ($15 per 25,000). Linux Docker resource classes: Small 5 credits/min, Medium 10, Large 20, XLarge 40, 2XLarge 80; macOS M4 Pro Medium 200, Large 400 credits/min (20-40x Linux rate). Free tier: 30,000 credits/mo, 5 users, 30x concurrency. Performance plan: $15/mo base + $15/user/mo, 80x concurrency, overage at $0.0006/credit. A 10-person team running ~20,000 Linux build-minutes/mo (Medium resource class) lands near $192/mo on Performance ($15 base + $75 for the 5 seats beyond the included 5 + $102 credit overage). Config schema has held at version 2.1 since 2019. G2 user rating: 4.4/5 (509 reviews). Current version/status: SaaS continuously deployed; self-hosted CircleCI Server v4.10.0 (2026). License: proprietary SaaS (self-hosted Server under commercial license). Pricing: Free: 30,000 credits/mo, 5 users, 30x concurrency; Performance: $15/mo base + $15/user/mo plus $15 per additional 25,000 credits (80x concurrency); Scale: custom annual billing, unlimited concurrency and GPU access. Maintained by Circle Internet Services, Inc. — private company, CEO Jim Rose, ~358 employe

Also known as: circle-ci

🧊Why learn CircleCI?

Pick CircleCI when a 5-20 engineer team runs Docker-heavy build/test pipelines and needs Large/XLarge resource classes plus layer caching and test splitting to cut wall-clock time — the credit overhead pays for itself in developer-hours saved. Skip it for solo devs, OSS maintainers, or pre-revenue startups: GitHub Actions gives unlimited free minutes on public repos and simpler $0.008/min private billing, undercutting CircleCI's credit math until volume climbs. If your whole stack already lives in GitLab, GitLab CI's flat $0.01/min beats CircleCI's variable resource-class pricing too. Honest weakness, straight from G2 reviewers: credit burn from Docker layer caching and macOS runners is opaque, with no built-in warning before a team blows through its monthly allotment. Known weakness: Credit consumption from Docker layer caching and macOS runners is opaque — G2 reviewers report costs spiking unpredictably with no built-in warning before a team's monthly credits run out.

See how it ranks →

Compare CircleCI

CircleCI vs Github Actions→CircleCI vs Gitlab Ci→CircleCI vs Jenkins→

Learning Resources

CircleCI Configuration Reference

CircleCI Price List

CircleCI Orbs Registry

CircleCI Server Release Notes

Related Tools

Docker Github Actions Gitlab Ci Kubernetes Yaml

Alternatives to CircleCI

Github Actions Gitlab Ci Jenkins

Other CI/CD Tools

.env is a file format and tool used to store environment variables, which are key-value pairs that configure application settings like API keys, database URLs, and other sensitive or environment-specific data. It allows developers to separate configuration from code, making applications more secure and portable across different environments (e.g., development, testing, production). Tools like dotenv in Node.js or python-dotenv in Python parse .env files to load these variables into the application's environment at runtime.

.htaccess (Hypertext Access) is a configuration file used on Apache web servers to control directory-level settings, such as URL redirection, access control, and performance optimizations. It allows developers to override global server configurations for specific directories without modifying the main server configuration files. This file is commonly used for tasks like enabling HTTPS, blocking IP addresses, or setting custom error pages.

.htaccess (Hypertext Access) is a configuration file used on Apache web servers to control directory-level settings, such as URL redirection, access control, and performance optimizations. It allows developers to override global server configurations for specific directories without modifying the main server configuration files. This file is commonly used for tasks like password protection, custom error pages, and enabling features like mod_rewrite for URL manipulation.

.htaccess Redirect

.htaccess redirect is a server-side configuration technique using the .htaccess file on Apache web servers to manage URL redirections, such as redirecting old URLs to new ones, enforcing HTTPS, or handling errors like 404 pages. It operates through directives like Redirect, RedirectMatch, and RewriteRule, allowing developers to control traffic flow without modifying server-wide settings. This method is essential for SEO, user experience, and maintaining link integrity during website migrations or updates.

.NET Interactive

.NET Interactive is an open-source tool that enables interactive programming experiences across multiple languages (C#, F#, PowerShell, SQL, HTML, JavaScript) within notebooks like Jupyter, Visual Studio Code, and Azure Data Studio. It allows developers to create and share executable documents that combine code, visualizations, and narrative text, facilitating data exploration, documentation, and teaching. The tool integrates with the .NET ecosystem, providing rich output capabilities and extensions for data science and machine learning workflows.

.NET Profiling Tools

.NET profiling tools are software utilities used to analyze the performance, memory usage, and behavior of .NET applications during execution. They help developers identify bottlenecks, memory leaks, and inefficiencies by collecting data on CPU usage, garbage collection, thread activity, and method execution times. These tools are essential for optimizing .NET applications to ensure they run efficiently and reliably in production environments.