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Top #2 Web Development Company in the world

We are big on creating eminently successful businesses - products we have developed from scratch so far have raised in excess of $495,000,000 in funding!

No one failed projects

In addition, we were named as "Best & innovative development company on the market" (c) RBC

Plus, we became "Top #2 Web Development Company in the world" (c) Manifesto

Under-the-hood:

  • $10,000+
  • $50 - $99 / hr
  • 50 - 249
  • London, England
  • Founded 2008

1 Locations

  • London , England
Total Reviews
13
Average Referral Rating
4.9 /5
Most Common Project Size

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    4xxi Review Insights

    Overall Review Rating

    4.9
    • Quality 4.9
    • Schedule 4.8
    • Cost 4.8
    • Willing to Refer 4.9

    Top Mentions

    • high-quality work (7)
    • communicative (4)
    • proactive (4)
    • timely (4)
    • unique expertise (4)
    • well-organized projects (4)
    • exceptional performance (3)
    • reasonable pricing (3)

    Review Highlights

    • Strategic Insights and Recommendations

      4xxi is not just an execution partner but also provides strategic insights and recommendations. Clients valued their ability to look at projects from different angles and offer innovative ideas to enhance the final product.

    • Innovative and Creative Solutions

      4xxi is recognized for their innovative and creative approach to problem-solving. They often go beyond the scope to deliver unique solutions that meet and exceed client expectations.

    • Challenges with Initial Project Management

      Some clients experienced initial challenges with project management, including the need to rotate project managers. These issues were typically resolved over time, leading to more effective collaborations.

    • Commitment to Client Success

      Many clients emphasized 4xxi’s dedication to their projects, highlighting the team's passion, energy, and commitment to client success. This dedication often led to successful product launches and positive feedback from end-users.

    • High-Quality Deliverables

      Clients consistently reported high satisfaction with the quality of 4xxi’s deliverables, including bug-free software, well-architected solutions, and robust performance. This reflects their commitment to excellence.

    • Comprehensive Development Services

      4xxi provides comprehensive development services, including frontend and backend development, QA, project management, and design. This full-service approach ensures cohesive and well-integrated solutions.

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    Mobile App Dev for Social Platform

    • Mobile App Development
    • $200,000 to $999,999
    • Jan. 2020 - Ongoing
    5.0
    Quality
    5.0
    Schedule
    5.0
    Cost
    5.0
    Willing to Refer
    5.0

    "They are a fantastic team and we wouldn't be where we are today without them!"

    Nov 11, 2020
    Director & Co-Founder, Challenge Social
    Josh Lewis
    • Software
    • United Kingdom
    • 1-10 Employees
    • Online Review 
    • Verified

    4xxi was hired by a social platform to redevelop their mobile app for iOS and Android. They were also tasked with coding their website and provide maintenance and support.

    Custom Software Development for Advertising Firm

    • Custom Software Development
    • $200,000 to $999,999
    • June 2013 - Sep. 2017
    5.0
    Quality
    5.0
    Schedule
    5.0
    Cost
    5.0
    Willing to Refer
    5.0

    “I was very impressed by the quality of their work and their development speed.”

    Jul 24, 2018
    VP of Engineering, Virool inc
    Alexander Petrov
    • Advertising & marketing
    • San Francisco, California
    • 51-200 Employees
    • Online Review 
    • Verified

    4xxi provided UI development services for various customer dashboards for an online platform. The team created accessible and manageable dashboards for analytics, billing, campaign management, and reports.

    Platform Dev for Auditing Firm

    • Web Development
    • $50,000 to $199,999
    • Feb. - May 2017
    5.0
    Quality
    5.0
    Schedule
    5.0
    Cost
    5.0
    Willing to Refer
    5.0

    "They can look at a startup from different angles and provide insight on how to improve."

    Apr 20, 2018
    Owner, Auditing Firm
    Anton Petrov
    • Financial services
    • Russia
    • 1-10 Employees
    • Phone Interview 
    • Verified

    4xxi developed a complex platform for auditing services, handling the programming and design for the whole infrastructure. They provided all documentation and will handle the next version’s build in the future.

    Intranet Dev for Private Investment Firm

    • Web Development
    • $50,000 to $199,999
    • Feb. 2015 - Ongoing
    5.0
    Quality
    5.0
    Schedule
    5.0
    Cost
    5.0
    Willing to Refer
    5.0

    “Working with 4xxi has been one of the best commercial experiences of my business life.”

    Jan 19, 2018
    President, Emanuel Quant Services
    Steven Emanuel
    • Financial services
    • New York City, New York
    • 1-10 Employees
    • Phone Interview 
    • Verified

    4xxi integrated numerous data sources into one tool that displayed all the desired information in a singular report. The project consisted of an iterative and collaborative process.

    Web Dev for VPN Firm

    • Web Development
    • Confidential
    • Mar. 2017 - Ongoing
    5.0
    Quality
    5.0
    Schedule
    5.0
    Cost
    5.0
    Willing to Refer
    5.0

    “4xxi builds software to their own quality standards, which are high even compared to Silicon Valley.”

    Oct 20, 2017
    Director of Product, AnchorFree
    Sergey Fedorov
    • IT Services
    • San Francisco, California
    • 51-200 Employees
    • Phone Interview 
    • Verified

    4xxi assisted with a VPN website update. The team provided consultation guidance, then collaborated in designing and developing the new platform using PHP and JavaScript.

    Web Dev for Financial Services Firm

    • Web Development
    • Confidential
    • Oct. 2015 - Ongoing
    5.0
    Quality
    5.0
    Schedule
    4.5
    Cost
    5.0
    Willing to Refer
    5.0

    "They are so responsive, thoughtful, great communicators, and really challenge and ask the right questions."

    Sep 19, 2017
    General Manager, WorthFM
    Emily Jipson
    • Financial services
    • Philadelphia, Pennsylvania
    • 1-10 Employees
    • Phone Interview 
    • Verified

    4xxi built a robo-advisory platform using Ruby and React. They were responsible for project management, backend development, architecture, some design and QA.

    Cross-Platform App Dev for Productivity App

    • Mobile App Development
    • Confidential
    • June 2013 - Ongoing
    5.0
    Quality
    5.0
    Schedule
    4.5
    Cost
    5.0
    Willing to Refer
    5.0

    “We would not be here today if 4xxi was not involved in this project.”

    Sep 15, 2017
    CEO, Productivity App
    Anonymous
    • Software
    • New York City, New York
    • 1-10 Employees
    • Phone Interview 
    • Verified

    4xxi developed a cross-platform app for iOS, Android, and the web. The app is designed for coordinated communication in crisis situations. 

    iOS and Android Native Dev for Concierge Service App

    • Mobile App Development
    • $50,000 to $199,999
    • Aug. 2016 - July 2017
    5.0
    Quality
    4.5
    Schedule
    5.0
    Cost
    5.0
    Willing to Refer
    5.0

    "[T]hey go that extra mile to answer questions and solve problems."

    Sep 6, 2017
    CEO, Iterium
    Kirill Garbar
    • IT Services
    • London, England
    • Phone Interview 
    • Verified

    Using a framework built in PHP and Symfony, 4xxi built mobile concierge apps for the iOS and Android platforms. The projects involved continuous integration, back-end development, and scripting. 

    Web Dev for Ratings & Reviews Platform

    • Web Development
    • $200,000 to $999,999
    • Sep. 2012 - Ongoing
    4.5
    Quality
    4.5
    Schedule
    4.5
    Cost
    4.0
    Willing to Refer
    4.5

    "Within the project guidelines and deliverables they excelled, came up with suggestions and were proactive."

    Aug 31, 2017
    Former CEO, Industry Index
    Gayle Meyers
    • Advertising & marketing
    • New York City, New York
    • Phone Interview 
    • Verified

    4xxi acted as the engineering team, building an online platform from the ground up. They provided frontend and backend development and API integration. The platform grew from zero users to over 5,000 users. 

    Web Dev for Health & Wellness Sharing Platform

    • Web Development
    • $50,000 to $199,999
    • July 2016 - Ongoing
    5.0
    Quality
    5.0
    Schedule
    5.0
    Cost
    5.0
    Willing to Refer
    5.0

    "They deliver on every aspect they say they are going to.”

    Aug 28, 2017
    Founder, Nutmeg Asprin
    Mara Landis
    • Consumer Products
    • New York City, New York
    • 1-10 Employees
    • Phone Interview 
    • Verified

    4xxi built an AWS and Digital Ocean website, and are currently working on the redesign. They provided feedback to help develop a rewards functionality and encourage a back-to-basics approach for improved UI.

    Locations (1)

    41 - 49

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