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An e-commerce manager and a developer in Riyadh compare two printed checkout designs before a gradual release.

Vercel · SDKs

A new checkout goes to every customer at once, and orders drop. Show it to a few first.

A redesign, a new form, a new menu. Today it goes live for everyone, and if it hurts, a developer has to roll it back. With the Flags SDK, the change ships switched off. You turn it on for some visitors, compare the results, then widen it or switch it off. No redeploy either way.

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Salesforce consulting partner since 2010 · MVP Hall of Fame · 200+ agents in production · UAE, India and US desks

The problem

Where a launch goes wrong today.

What Flags SDK is

Flags SDK, in plain words.

Facts from Vercel’s own pages, checked on 16 October 2026. The sources are at the end of this page.

What it is
A free, open-source library for Next.js and SvelteKit. It is a library in your code, with no hosted runtime API to call.
How a flag works
Each flag has a key and a decide function that can read the request, such as a cookie or a header.
Providers
Works with Vercel Flags, LaunchDarkly, Statsig, ConfigCat, DevCycle, Flipt, a custom adapter, or no provider at all.
Fast pages
The precompute pattern builds a static version of the page for each flag combination.
Checking it
Flags Explorer in the Vercel Toolbar lets your team override a flag on the page, with no code change.
Vercel Flags price
As of 16 October 2026: Hobby includes 10,000 flag requests a month; Pro pays $0.03 per 1,000. The SDK itself is free.

How it works

From an idea to a feature everyone has.

Five steps. The feature is live in the code from day one, but customers only see it when you turn it on.

Five steps: define the flag in code, decide who sees it, deploy switched off, turn it on for some visitors, watch and widen.

Infographic

The same steps are written out below.

Step by step

What happens at each step.

  1. Define

    Define the flag in code

    A key and a decide function, next to the feature it controls.

  2. Decide

    Decide who sees it

    By cookie, country, logged-in account or an even split.

  3. Deploy

    Deploy with it switched off

    The new feature is in production, hidden from customers.

  4. Turn on

    Turn it on for some visitors

    In the flag provider, with no redeploy.

  5. Widen

    Watch results, then widen

    Compare in Web Analytics and Runtime Logs, then open it to everyone or switch it off.

How it fits together

Where flags sit between your visitors and your code.

The flag is defined in your Next.js or SvelteKit app. The on and off switch lives in a provider: Vercel Flags or one you already pay for. Your team checks both versions with Flags Explorer, and the results show in Web Analytics.

Visitors reach your app with the Flags SDK, which reads a flag provider; your team checks with Flags Explorer and results show in Web Analytics.

Infographic

Where it sits next to the systems you run today.

Use cases · worked examples

One worked example in each industry.

How Flags SDK fits into the work of the industries we serve, one step at a time.

  1. A new checkout ships switched off, the team tries both, some shoppers see it, then it is widened or switched off.

    Example 1 · Retail and e-commerce, Riyadh · Infographic

    E-commerce manager at a Riyadh fashion retailer

    Today: The last checkout redesign went to every shopper on a Thursday. Orders fell over the weekend and nobody could say if the design was to blame.

    After: The new one-page checkout ships behind a flag. A small share of shoppers see it first, and the team compares completed orders before anyone else gets it.

    Worked example, step by step

    1. Sun 09:00Developer. Deploys the new checkout behind a flag, switched off for shoppers.
    2. Sun 10:00E-commerce manager. Tries both checkouts on a preview with Flags Explorer.
    3. Sun 12:00E-commerce manager. Turns the new checkout on for a small share of visitors in the flag provider.
    4. Mon to WedWeb Analytics. Shows completed orders for each checkout side by side.
    5. Thu 09:00E-commerce manager. Opens it to every shopper, with no redeploy.

    The new checkout reaches everyone only after the orders show it works.

    Retail and e-commerce
  2. A new maintenance request form is switched on for one building first, checked by the manager, then opened to every building.

    Example 2 · Property management, Dubai · Infographic

    Community manager at a Dubai property management company

    Today: A new online maintenance form is ready. Last time a new form went to every building at once, a broken photo upload meant a week of phone calls.

    After: The form is shown to the tenants of one building first. Requests land in Salesforce as cases. Once it holds up, every building gets it.

    Worked example, step by step

    1. Mon 08:00Developer. Adds a flag that shows the new form to tenants of one building.
    2. Mon 08:30Community manager. Checks the new form with Flags Explorer before any tenant sees it.
    3. Mon 09:00Tenant. Logs a leaking AC unit on the new form, with two photos.
    4. Mon 09:01Salesforce. Creates the case for the maintenance team.
    5. Week 2Community manager. Turns the form on for every building in the provider.

    Any problem with the form shows up in one building, not across the portfolio.

    Property management
  3. Two menu layouts are shown to half the visitors each for a week, orders are compared, and the winner stays.

    Example 3 · Restaurants and cafes, Kochi · Infographic

    Owner of a cafe chain with three branches in Kochi

    Today: The team argues about the online menu. One side wants photos first, the other wants the bestsellers first. Nobody can prove either.

    After: A flag splits visitors evenly between the two layouts for a week. The owner keeps the one that brings more orders.

    Worked example, step by step

    1. Mon 10:00Developer. Adds a flag with two menu layouts, split evenly.
    2. Mon 10:05Developer. Uses the precompute pattern so both layouts stay fast static pages.
    3. Mon to SunVisitors. Each sees one layout and keeps it on return visits.
    4. Sun 18:00Owner. Compares orders from each layout in the analytics.
    5. Mon 09:00Developer. Keeps the winning layout and removes the flag.

    The menu is chosen by a week of orders, and the losing layout leaves the code.

    Restaurants and cafes
Examples of the work, not client stories. Times in each example show the order of events, not a measured result.

Is it for you

When Flags SDK fits, and when it doesn’t.

Good fit

Not for you yet

Your site or app is on Next.js or SvelteKit
Your site is on another framework: Vercel names only Next.js and SvelteKit
A bad release costs you orders or calls
You have too little traffic to compare two versions
You want to test two designs on real visitors
Nobody will remove old flags once a test ends
You already use a flag provider, or want Vercel Flags
You only need a page builder’s own A/B test

What Mindcat does

We build it, then we run it.

The assessment is free: a short read of the org and a written note. If you go ahead, the first build week is a fixed AED/SAR 14,900 (about USD 4,050), credited in full when you sign the build within 60 days. After go-live, we keep it patched, watched and changing every month.

Read next

What it works with.

FAQ

What teams ask about Flags SDK.

Does the Flags SDK cost money?
No. The SDK is free and open source. If you use Vercel Flags as the provider, as of 16 October 2026 Hobby includes 10,000 flag requests a month and Pro pays $0.03 per 1,000. Hobby is for non-commercial use only, so a business site needs Pro.
Can we keep LaunchDarkly or Statsig?
Yes. The SDK has adapters for LaunchDarkly, Statsig, ConfigCat, DevCycle, Flipt and Vercel Flags, and a custom adapter for anything else.
Does it work with our Nuxt or plain React site?
Vercel names Next.js and SvelteKit. For any other framework we would not promise it, and we would look at your provider’s own SDK first.
Do flags slow the page down?
They do not have to. The precompute pattern builds a static version of the page for each flag combination, so visitors still get a fast page.
How many flags can we have?
On Vercel Flags, Hobby allows 100 flags and Pro allows 10,000. We keep far fewer by removing each flag once its test ends.

Sources

Where these facts come from.

Start here

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Salesforce consulting partner since 2010 · MVP Hall of Fame · 200+ agents in production · UAE, India and US desks

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