Every successful ecommerce project starts with a thorough understanding of what you actually need to build. The difference between projects that launch on time and on budget and those that spiral into chaos almost always comes down to how well requirements were documented before development began.
This guide covers the functional requirements every new ecommerce site needs to consider, organized by category so you can build a comprehensive checklist before engaging any development partner or making platform decisions.
Ecommerce System Requirements: Functional and Non-Functional
Ecommerce system requirements split into two categories that need to be specified separately because they're built and validated in different ways.
Functional requirements describe what the system does: catalog management, cart and checkout, customer accounts, order processing, onsite search, promotions, returns. Functional requirements are typically the bulk of an ecommerce requirements document and the easiest to enumerate because they map directly to user actions and admin workflows. Most of this guide covers functional requirements, organized by the area of the system they belong to.
Non-functional requirements describe how the system performs: performance under load, scalability during traffic spikes, security and compliance, reliability and uptime, accessibility, maintainability, and search engine indexability. Non-functional requirements are easy to under-specify because they feel like defaults, but they are where most ecommerce projects ship with hidden gaps that surface only at peak season or after the first compliance audit.
The non-functional requirements every ecommerce store needs to specify before development starts:
- Performance: Sub-3-second Time to Interactive on 4G connections, Google PageSpeed score above 80 on mobile, Core Web Vitals (LCP, CLS, INP) within Google's green thresholds for the templates that drive the most organic traffic.
- Scalability: Ability to absorb a 10x traffic spike (Black Friday, a viral product, an influencer drop) without queueing, errors, or degraded checkout completion rates.
- Security and compliance: SSL across the entire domain, PCI DSS compliance on the payment path, GDPR/CCPA data handling, ongoing patch management for the platform and every third-party app.
- Reliability: 99.9% uptime target, automated monitoring with alerting on checkout failures and core-page errors, documented recovery procedures.
- Accessibility: WCAG 2.2 Level AA conformance across templates, checkout, and user-generated content (see our ADA compliance guide for Shopify and BigCommerce merchants for what this involves in practice).
- SEO and indexability: Server-rendered HTML for product and category pages, canonical URLs, structured data, working sitemap and robots.txt, and a 301 redirect strategy that survives any future replatform.
- Maintainability: Theme code your next agency or in-house engineer can read, a documented integration architecture, and version-controlled customizations that survive platform updates.
The functional requirements specific to your business model are unique to your store. The non-functional requirements above are largely universal: every ecommerce site needs them, and they should be in your requirements document before any platform or vendor evaluation begins.
Foundation: The Non-Negotiables
Platform and Hosting
Platform selection is a strategic decision, not just a technical one. The right platform depends on your product catalog complexity, B2B vs. D2C model, international requirements, and integration needs. For most mid-market merchants, Shopify Plus offers the best combination of capability, ease of use, and total cost of ownership. For more complex requirements, evaluate BigCommerce or a headless architecture. If you're not building net-new but moving off an existing platform, our platform migration framework covers what changes.
Performance
Page speed isn't a nice-to-have. It directly impacts conversion rates and search rankings. Target a Google PageSpeed score above 80 on mobile, with sub-3-second Time to Interactive on 4G connections, and pay attention to Core Web Vitals (LCP, CLS, INP) which are now the primary signal Google uses. This requires discipline from day one: optimized images, minimal render-blocking scripts, efficient Liquid code, and careful app selection.
Security and Compliance
- SSL/HTTPS across the entire domain (not just checkout)
- PCI DSS compliance for payment processing
- ADA/WCAG 2.2 Level AA accessibility compliance. For a detailed breakdown of what this means on Shopify and BigCommerce, see our guide to ADA compliance for ecommerce merchants
- GDPR cookie consent for EU visitors
- CCPA opt-out mechanisms for California residents
User Experience and Design
Homepage
The homepage needs to answer three questions immediately: Who are you? What do you sell? Why should I care? It should establish brand narrative through creative assets, surface your best products and current promotions, and direct visitors toward their likely shopping intent.
Mobile Experience
Mobile drives the majority of ecommerce traffic, and for many demographics and product categories it exceeds 80%. Mobile design isn't a responsive afterthought; it needs to be the primary design surface. Test checkout completion on mobile specifically. This is where most mobile conversion is lost.
Navigation and Search
For catalogs with more than 100 SKUs, onsite search becomes a critical conversion tool. Consider a dedicated search solution (Searchanise, Boost Commerce, or similar) that supports typo tolerance, synonym handling, and merchandising rules rather than relying on Shopify's basic native search.
Marketing and Analytics Infrastructure
Analytics
- Google Analytics 4 with enhanced ecommerce event tracking (view_item, add_to_cart, begin_checkout, purchase)
- Google Tag Manager for manageable tag deployment
- Server-side tracking for accurate attribution in a cookieless world
Pixels and Tracking
Identify every advertising platform you'll use and ensure proper pixel implementation: Meta (Facebook/Instagram), Google Ads, TikTok, Bing, and any DSPs you work with. These need to fire accurately on the right events (particularly the purchase event) for your ad platforms to optimize effectively.
Email Marketing
- Choose your ESP before launch: Klaviyo (most common for Shopify), Listrak, or Mailchimp
- Set up transactional flows at launch minimum: order confirmation, shipping notification, delivery confirmation
- Configure abandoned cart recovery before your first visitor arrives
- Build a welcome series for new email subscribers
Operations: Shipping and Payments
Shipping Configuration
- Document all your shipping zones, carriers, and rate structures
- Decide between flat rate, calculated (real-time carrier rates), or free shipping thresholds
- Configure shipping for international markets if applicable
- Address dimensional weight pricing if you ship large items
Payment Methods
Offer more than credit cards. The standard modern ecommerce payment stack includes:
- Credit/debit cards via Shopify Payments or a payment gateway
- PayPal (still used by a significant buyer segment)
- Apple Pay and Google Pay (one-tap checkout significantly improves mobile conversion)
- Buy Now Pay Later: Klarna, Afterpay, or Affirm (especially important for higher AOV products)
Advanced Features to Plan For
Not every store needs these at launch, but knowing which you'll eventually need helps you choose the right platform and architecture from day one:
- International selling: Multi-currency, multi-language, international shipping, localized content
- Product reviews: Embedded reviews build conversion trust significantly. Plan for a review platform from launch
- Loyalty program: Repeat purchase rates improve substantially with structured loyalty mechanics
- Returns management: Self-service returns reduce customer service volume and improve customer satisfaction
- B2B capabilities: If you have any wholesale customers, plan for this before platform selection. Retrofitting B2B on a D2C architecture is painful. See our overview of Shopify B2B development for what a B2B-ready build covers
- Store locator: Required for any brand with physical retail presence
- Subscription products: If any products are candidates for subscription models, evaluate platforms and apps before launch
Backend Integrations
The systems that need to connect to your ecommerce platform determine your integration architecture:
- ERP: Products, pricing, inventory, and order data needs to flow bidirectionally. This is the most complex integration for most merchants. Budget accordingly.
- 3PL / Warehouse Management: If you use a third-party fulfillment provider, orders need to route there and tracking needs to come back.
- Shipping software: ShipStation, EasyPost, or Shippo for rate shopping and label generation if you ship in-house.
- Tax engine: Avalara or Vertex for merchants with complex multi-state tax obligations.
The Requirements Document
Pull all of the above into a structured requirements document before engaging any development partner. A detailed requirements document lets you:
- Get accurate quotes (not ballpark estimates that balloon)
- Evaluate platforms against your actual needs
- Identify integration complexity early
- Set realistic timelines
- Reduce mid-project scope changes
Merchants who invest in thorough requirements documentation before development begins consistently have better outcomes (shorter timelines, fewer surprises, and lower total project costs) than those who figure it out as they go.
Frequently Asked Questions
Shopify or BigCommerce for a new ecommerce site?
For most mid-market merchants, Shopify Plus offers the best combination of capability, ease of use, and total cost of ownership. BigCommerce is a stronger fit for stores with complex B2B catalog structures, native multi-storefront needs, or merchants who want to avoid Shopify's transaction-fee model on non-Shopify gateways. The right answer comes from matching platform strengths to your actual catalog, B2B/D2C mix, and integration footprint, not from a generic preference.
What's the minimum viable feature set for a new ecommerce store?
At launch you need: a transactional storefront with product detail and category pages, a working checkout (cards plus at least one wallet like Apple Pay or PayPal), SSL across the whole domain, Google Analytics 4, an email service provider with order confirmation and abandoned cart flows, shipping zones and rates configured for every market you sell to, and a tax setup that matches your nexus footprint. Everything else (reviews, loyalty, subscriptions, international, B2B) can be phased in, but should still be planned for in the architecture so it doesn't require a re-platform later.
How long does a new ecommerce build take?
A standard Shopify Plus build with a custom theme and three to five integrations typically takes 12 to 20 weeks from kickoff to launch. Heavily customized builds with B2B, ERP integration, or headless architecture run 20 to 36 weeks. Timelines almost always extend when requirements aren't documented before development starts. Investing two to four weeks in a thorough requirements document up front shortens the overall project by significantly more than it costs.
Should we launch with B2B from day one or add it later?
If you have any wholesale customers, plan for B2B before platform selection. Retrofitting B2B onto a D2C-only architecture is expensive and constrains your theme and data model. Shopify Plus and BigCommerce both support native B2B. The choice is whether to launch with the B2B channel live or stand it up shortly after D2C goes live. Either way, do not pick a platform without confirming it can serve your B2B use case.
Do I need a headless storefront?
For most mid-market stores, no. Headless adds development cost, ongoing maintenance, and complexity to merchandising and content workflows. The cases where headless is the right call: you have unique storefront UX requirements that a Shopify or BigCommerce theme can't deliver, you need to share commerce data with multiple non-storefront surfaces (kiosks, mobile apps, B2B portals), or your team has the in-house engineering capacity to maintain it long-term. If none of those apply, a well-built native theme will perform better than most agencies' headless builds.
What's the most common mistake when building a new ecommerce site?
Skipping the requirements document. Teams that jump straight into design and development without a written feature list, integration list, and operational playbook routinely run into mid-project scope changes, missed integrations discovered weeks before launch, and ballooned timelines. The second most common: under-investing in mobile checkout testing. Most conversion loss happens between cart and order confirmation on a phone, and most pre-launch QA happens on desktop.