Conversion
The Best Ecommerce Web Design and Build Agencies
Updated October 17, 2026 · 5 agencies · How we build these lists
The short answer
Ecommerce build agencies differ by what makes the project risky. Barrel is the pick when the migration itself is the risk, with 100+ Shopify migrations and a CPG focus. Darkroom pairs development with media and contribution-profit measurement. Avenue Z runs Shopify design and CRO next to its commerce practice. KlientBoost builds landing pages as part of the media buy. Munro handles B2B sites where the conversion is a qualified lead rather than a cart.
The most expensive mistake in an ecommerce rebuild is treating it as a design project when it is a revenue project. A beautiful site that converts worse than the one it replaced is a common and costly outcome. The agencies here all pair the build with something that keeps it honest, whether that is conversion testing, media, or migration experience.
At a glance
| Agency | Best for |
|---|---|
| Barrel | CPG brands where the Shopify migration itself is the risk |
| Darkroom | Brands that want the build connected to media and margin |
| Avenue Z | Brands rebuilding on Shopify alongside PR and search |
| KlientBoost | Brands whose landing pages need to answer to the ad account |
| Munro | B2B sites where the conversion is a qualified lead |
Agency profiles
Barrel
Best for CPG brands where the Shopify migration itself is the risk
New York, NY, with Los Angeles, Toronto, and Philadelphia
- Shopify Plus agency partner
Barrel reports more than 100 Shopify migrations across two decades and states Shopify Plus agency partner status, with named work for McCormick, KIND Snacks, L'Oréal Paris, and Waterloo. It also builds non-DTC sites whose job is driving shoppers to retail, which most ecommerce shops do not do.
Darkroom
Best for brands that want the build connected to media and margin
New York, NY
Darkroom pairs website development and CRO with its media and measurement practice, and states it manages to contribution profit. The fit when the conversion fix requires building something rather than editing a page, and when the build needs to answer to revenue.
Avenue Z
Best for brands rebuilding on Shopify alongside PR and search
New York, Miami, and Orlando
Avenue Z runs Shopify design and development with conversion rate optimization as a named ecommerce service, sitting next to its performance media, PR, and AI search practice. Suits brands treating a rebuild as part of a wider visibility push.
KlientBoost
Best for brands whose landing pages need to answer to the ad account
Costa Mesa, CA
KlientBoost treats landing page design and CRO as part of the media buy rather than a separate project, and publishes a quarterly rate of hitting client goals with a commitment to add resources at no cost when it misses.
Worth knowing: Oriented to landing pages and conversion paths rather than full catalog ecommerce builds.
Munro
Best for B2B sites where the conversion is a qualified lead
Glasgow, Scotland
- Google Partner
- SharpSpring Platinum Partner
Munro builds websites alongside CRM automation and demand generation for B2B and considered purchases, with named work for Dell and MentorCliq. Relevant when the site's job is a form, a demo request, or a quote rather than a checkout.
Worth knowing: Not a transactional ecommerce build agency.
What we compared
- Migration and replatforming experience, where most of the real risk sits
- Whether conversion testing is part of the build or a later phase
- Published platform partner status, particularly Shopify tiers
- Whether the agency can see the traffic source feeding the site
- Omnichannel capability where the site supports retail as well as DTC
- Named work at a comparable catalog size and complexity
Frequently asked questions
- How much does an ecommerce website build cost?
- A Shopify theme customization commonly runs $15,000 to $40,000. A custom build or a Plus migration typically falls between $50,000 and $250,000, and complex replatforms with ERP or custom integrations go well beyond that. The largest cost variables are integrations and data migration, not page design, so get those scoped explicitly.
- How do I avoid a redesign that lowers conversion rate?
- Do not change everything at once. Establish a baseline, keep the elements that existing data shows are working, and roll out structural changes in phases you can measure. Ask any agency how it will validate the new site against the old one, and treat a flat answer as a warning. Redesigns that drop conversion usually do so because nobody tested the assumptions the design was built on.
- What does Shopify Plus partner status actually mean?
- It indicates Shopify has recognized the agency as meeting its requirements for working on Plus, which generally include a track record of Plus builds and maintaining client accounts in good standing. There are tiers above base partner status, but agencies are inconsistent about naming theirs publicly, so confirm the current tier directly rather than relying on a badge image.
- Should the agency that builds the site also run the ads?
- It helps when conversion is the problem, because the people changing the page can see which traffic converts and test against the source rather than in aggregate. It matters less if your build is primarily a brand or catalog project, where specialist craft is worth more than channel feedback.