Overview

Fluid UI is a browser-based mockup and prototyping tool for turning mobile-app concepts into interactive demonstrations. It suits designers and small product teams that need to share ideas and gather feedback; its review and collaboration tools are useful, but the paid plans’ project and user-license caps call for a close fit check.

Users can create, edit, preview, share and export mockups, then add gestures to make web and mobile prototypes navigable. A broad component library and several animation effects help communicate both appearance and flow, while cloud-saved work supports collaboration.

Key features

Component libraries: More than 2,000 built-in components cover Material Design, iOS, Windows and wireframe libraries. This gives designers multiple established starting points, rather than tying them to one visual system.
Interactive prototyping: Taps, swipes, clicks and other gestures can link screens, with page effects including pop in, fade in, flip and show. These tools help convey intended behavior before a product is built; they are for mockups and prototypes, not a finished application.
Collaboration: Cloud-saved projects are accessible to team members, and real-time collaborative prototyping is supported. That makes Fluid UI more useful for shared design work than a mockup tool centered on an individual’s files.
Review and testing: Reviewer mode supports shared click-throughs, chat, annotations and comments, and the service supports remote user-testing sessions. These features give teams a way to collect feedback around a prototype rather than relying only on static screens.
Access and support: Fluid UI runs in Firefox and Chrome, has an installable desktop client, and offers Android and iOS preview apps. Built-in live chat support is available 16 hours a day.
Data handling: Fluid UI says pages use industry-standard 256-bit encryption for data sent to the service, and that it continuously saves projects with daily, weekly and monthly backups. Projects can be restored from any save in the editor. Realex Payments processes and stores card details; Fluid UI says it does not keep card details on its own servers. Its servers run in a Rackspace US data center, and account-data deletion can be requested by email.

Pricing

Fluid UI uses a freemium model with a free plan and a trial. The paid tiers are priced per month as shown, but the project and user-license limits are as important as the entry price when deciding whether a plan fits.

Free: Free forever, with a lifetime account.
Solo — $8.25/month: Includes 5 active projects, 1 user license and unlimited reviewers. It suits an individual who wants several live projects and feedback from others; unlimited reviewers do not mean multiple editing seats.
Pro — $19.08/month: Includes 10 projects, 1 user license, unlimited reviewers, and export, print and comment. The added output and commenting options make it a stronger fit for a solo practitioner delivering work, but it still provides only one user license.
Team — $41.58/month: Includes unlimited projects, 5 users, unlimited reviewers, export, print and comment, plus real-time team collaboration. This is the clearest fit for a small working group; teams larger than five need to account for the seat cap.

Solo and Pro keep the editing license to one person, so their low starting prices are less compelling for teams that need several contributors. Team removes the project cap and adds five seats, but costs more and still sets a limit on licensed users.

Platforms

Fluid UI is web-based, with Firefox and Chrome support, an installable desktop client, and Android and iOS preview apps. Its listed platform coverage also includes Linux, macOS and Windows. That range supports access across common desktop systems and mobile preview devices.

Who it's for

Fluid UI is aimed at people who need to communicate product ideas, including designers, entrepreneurs, developers, product managers and professors. Solo designers can use the one-license tiers while inviting unlimited reviewers; teams that want real-time collaboration should look at Team and compare its five-user allowance with their actual contributor count.

It is less suitable for a larger group that needs more than five licensed users on the listed Team plan, or for buyers who need a confirmed free-plan project and seat allowance before committing to a workflow.

Pros and cons

Pro: More than 2,000 components across four design-library categories provide a broad starting point for mobile and wireframe concepts.
Pro: Interactive gestures, animations, shared click-throughs and remote user-testing support cover several stages of presenting and reviewing a prototype.
Pro: Unlimited reviewers on the paid tiers let people gather feedback without consuming the listed user licenses.
Con: Solo and Pro both provide just one user license, limiting their usefulness for teams that need multiple editors.
Con: Team includes five users, so larger groups must weigh the seat limit against the plan’s unlimited projects and collaboration features.
Con: The free plan is described as free forever, but its project, user and feature allowances are not established, making it hard to assess as a durable option.

Alternatives

For a wider shortlist, compare UI design tools, Wireframing Software, Prototyping Software and Game UI Design Software.

Mockplus is another freemium option; its Basic plan gives 10 users and 10 active projects, which may suit a group prioritizing those allowances.
UXPin offers a limited free plan after its 14-day trial, with 2 prototypes and 50 AI credits; consider it if those limits match your starting needs.
Proto.io has a free plan limited to 1 user, 1 active project, 5 prototype screens, 10 MB of storage and no additional reviewers, making it a more constrained free starting point.
Marvel offers a free plan for 1 user and 1 project; it may suit a solo user whose initial work fits that allowance.
Penpot is a freemium alternative with web and self-hosted platforms.
Justinmind has a free plan with 1 project, unlimited screens and viewers, and UI design and wireframing.
ProtoPie has a free plan for 2 prototypes saved in Cloud, 8 scenes per prototype and 50 MB of Cloud storage.
Wondershare Mockitt offers a free plan with 1 workspace, 3 files and 200 AI credits per person.

Verdict

Fluid UI is a strong choice for solo designers and small product teams who want interactive mockups with built-in review, reviewer access and remote testing support. Its clearest advantage is the path from screens to shared, actionable feedback; its main drawback is that the lower paid tiers license just one user and Team stops at five. Choose it when those seat limits fit your group, and look elsewhere if they do not.

	Alloy	Fluid UI
Free plan	Yes	Yes
Free trial	No	Yes
Paid from	$20/mo	$8.25/mo
Open source	No	No
Platforms	extension	Android, iOS, Linux, macOS, Web, Windows
Free plan	Yes	Yes
Paid from	20 /user/mo	—
Interactive prototypes	Yes	—
User testing	Yes	—
Team collaboration	Yes	—
Platform support	both	—
Prototype sharing	both	—

Alloy vs Fluid UI

Alloy

Fluid UI