Shopify Development Guide: Themes, Apps, Functions & Headless

Shopify gives you four places to write code. Picking the wrong one is the single most expensive mistake we see on audits. Here's how we decide.

Themes (Liquid + Online Store 2.0)

• Use for: storefront UI, content, merchandising, anything tied to a page.
• Strengths: Fast to ship, native performance, marketing can edit sections without devs.
• Limits: Can't modify checkout (that's Functions/UI extensions), can't persist custom data structures (that's metafields/metaobjects).

Shopify Functions (Plus & non-Plus)

• Use for: discount logic, shipping/payment customization, cart and checkout validation, fulfillment routing.
• Strengths: Run inside Shopify's infrastructure, milliseconds, no app server to maintain.
• Limits: Function-specific APIs, sandboxed runtime (Wasm). Not for arbitrary backend logic.

Apps (Remix + Shopify CLI)

• Use for: admin UI, integrations with external systems, async jobs, anything that needs a database or background worker.
• Strengths: Full backend, OAuth, webhooks, billing. Can be private (your store only) or public.
• Limits: Performance overhead — keep storefront-rendered app blocks lean.

Headless (Hydrogen / Next.js + Storefront API)

• Use for: brands with content velocity needs, multi-region/multi-store complexity, sub-1.5s LCP requirements.
• Strengths: Total UI freedom, edge caching, better DX for senior frontend teams.
• Limits: You re-implement what theme gives you for free. Not a fit for most brands under $5M.

Quick decision tree

• "I need to change a PDP" → theme section.
• "I need a discount no app supports" → Shopify Function.
• "I need to sync inventory with my ERP" → app (private) or middleware.
• "I need 100% control over storefront UI" → headless (only if you can staff it).

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We build across all four layers for Shopify and Shopify Plus brands. Get a quote.