Netlify Platform Patterns

Quick Guide: Netlify deploys sites from Git with automatic builds, CDN distribution, and serverless compute. Use netlify.toml for all configuration (redirects, headers, build settings, function schedules, plugins). Serverless functions live in netlify/functions/ and use the standard (req: Request, context: Context) => Response signature. Edge functions run on Deno at the network edge for geo-personalization and request transformation. Use Netlify.env.get() for environment variables in functions — never process.env. Use Netlify Blobs for key-value storage accessible from functions and edge functions.

---

<critical_requirements>

CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST use Netlify.env.get() to access environment variables in functions — NOT process.env which is unavailable in the modern functions runtime)

(You MUST use the .mts file extension for serverless functions to get ES module support — .ts defaults to CommonJS unless "type": "module" is in package.json)

(You MUST use context.waitUntil() for post-response background work — work not passed to waitUntil may be cancelled when the response is sent)

(You MUST keep redirects and headers in netlify.toml — they are global and NOT scoped to deploy contexts)

</critical_requirements>

---

Examples

• Core Setup & Functions — netlify.toml, serverless functions, scheduled functions, background functions, response streaming
• Edge Functions & Blobs — edge function patterns, geo-personalization, middleware, Netlify Blobs storage
• Quick Reference — CLI commands, limits tables, redirects/headers syntax, build plugin structure

---

Auto-detection: Netlify, netlify.toml, netlify/functions, @netlify/functions, @netlify/edge-functions, @netlify/blobs, Netlify.env, netlify dev, netlify deploy, netlify-cli, edge function, Netlify Blobs, getStore, netlify build, netlify forms, data-netlify, netlify.app, deploy-preview, branch-deploy, Netlify Identity

When to use:

• Deploying sites and applications to Netlify's CDN and serverless platform
• Writing serverless functions (API endpoints, webhooks, scheduled tasks)
• Writing edge functions (geo-personalization, A/B testing, auth, request transformation)
• Configuring redirects, rewrites, proxy rules, and custom headers
• Storing data with Netlify Blobs (key-value, file uploads, metadata)
• Setting up build plugins for custom build pipeline logic
• Managing environment variables across deploy contexts (production, deploy-preview, branch-deploy)
• Configuring Netlify Forms for static site form handling

When NOT to use:

• Long-running compute exceeding 60 seconds (serverless) or 50ms CPU (edge) — use traditional servers
• Workloads needing persistent database connections — Netlify functions are stateless per invocation
• Applications requiring WebSocket connections (Netlify does not support persistent WebSockets)

Key patterns covered:

• netlify.toml configuration (build, redirects, headers, deploy contexts, plugins)
• Serverless functions with typed Context (geo, cookies, params, waitUntil)
• Scheduled functions with cron expressions
• Background functions for long-running tasks (up to 15 minutes)
• Response streaming for real-time output
• Edge functions on Deno runtime with geo and request transformation
• Netlify Blobs key-value storage (site-level and deploy-scoped)
• Environment variables with scopes and deploy context overrides
• Netlify Forms with honeypot spam filtering
• Build plugins with lifecycle hooks

---

Philosophy

Netlify is a Git-centric platform: push to a branch, Netlify builds and deploys automatically. Configuration lives in netlify.toml alongside your code. The platform provides three compute primitives:

1. Serverless Functions — Node.js-based, up to 60 seconds execution, 1 GB memory. For API endpoints, webhooks, form handlers, and scheduled tasks.
2. Edge Functions — Deno-based, 50ms CPU limit, run at the nearest edge node. For request/response transformation, geo-personalization, A/B testing, and authentication.
3. Background Functions — Same as serverless but async (client gets 202 immediately), up to 15 minutes. For long-running tasks like data processing and batch operations.

Key architectural decisions:

• netlify.toml is the source of truth — build commands, redirects, headers, function config, and plugin setup all live here. Settings in netlify.toml override the Netlify UI.
• Functions use web standard APIs — Request, Response, ReadableStream, URL. No proprietary request/response objects.
• Edge functions are middleware — they intercept requests, can modify them, and call context.next() to continue the chain. Return undefined to skip.
• Blobs for storage — Netlify Blobs provides key-value storage accessible from serverless functions, edge functions, and build plugins without external database setup.

When to use Netlify:

• Static sites, JAMstack apps, and full-stack applications with serverless backends
• Sites needing CDN distribution with automatic HTTPS
• Projects benefiting from deploy previews on every pull request
• Applications needing geo-based personalization at the edge

When NOT to use Netlify:

• CPU-intensive compute exceeding function time limits
• Applications needing persistent server processes or WebSockets
• Workloads requiring more than 1 GB memory per function invocation
• Data-heavy applications needing a collocated database (functions run in a single AWS region)

---

Core Patterns

Pattern 1: netlify.toml Configuration

All Netlify configuration lives in netlify.toml at the repository root. It controls builds, redirects, headers, function settings, deploy contexts, and plugins.

[build]
  command = "npm run build"
  publish = "dist"

[build.environment]
  NODE_VERSION = "20"

[functions]
  node_bundler = "esbuild"

[context.production.environment]
  API_URL = "https://api.example.com"

[context.deploy-preview.environment]
  API_URL = "https://staging-api.example.com"

Key rule: Redirects ([[redirects]]) and headers ([[headers]]) are global — they cannot be scoped to deploy contexts. Everything else ([build], [functions], [[plugins]]) supports context-specific overrides.

See examples/core.md for full netlify.toml with redirects, headers, and deploy contexts.

---

Pattern 2: Serverless Functions

Functions live in netlify/functions/ and use the standard Web API signature. Use .mts for ES module support.

// netlify/functions/hello.mts
import type { Config, Context } from "@netlify/functions";

export default async (req: Request, context: Context) => {
  const name = new URL(req.url).searchParams.get("name") ?? "World";
  return new Response(`Hello, ${name}!`, {
    headers: { "content-type": "text/plain" },
  });
};

export const config: Config = {
  path: "/api/hello",
};

Why good: Uses standard Request/Response APIs, typed Context provides geo/cookies/params, config.path maps custom routes instead of the default /.netlify/functions/hello path.

See examples/core.md for full function patterns with route params, POST handling, and error responses.

---

Pattern 3: Scheduled Functions

Scheduled functions run on a cron schedule. They receive a JSON body with next_run timestamp. They only run on published (production) deploys.

// netlify/functions/daily-report.mts
import type { Config } from "@netlify/functions";

export default async (req: Request) => {
  const { next_run } = await req.json();
  console.log("Running daily report. Next run:", next_run);
  // Perform scheduled work...
};

export const config: Config = {
  schedule: "@daily",
};

Limitation: 60-second execution limit. Cannot be invoked via URL. For longer tasks, use background functions triggered by a scheduled function.

See examples/core.md for cron expressions and netlify.toml schedule config.

---

Pattern 4: Background Functions

Background functions return a 202 to the client immediately and continue processing for up to 15 minutes. Name the file with a -background suffix.

// netlify/functions/process-background.mts
import type { Context } from "@netlify/functions";

export default async (req: Request, context: Context) => {
  const data = await req.json();
  // Long-running work — client already received 202
  await processLargeDataset(data);
  console.log("Background processing complete");
};

Key rule: The return value is ignored. The client gets 202 Accepted immediately. Use for data processing, batch operations, email sending, and webhook fanout.

---

Pattern 5: Edge Functions (Deno Runtime)

Edge functions run on Deno at the nearest edge node. They intercept requests and can modify, redirect, rewrite, or pass through to the origin.

// netlify/edge-functions/geo-redirect.ts
import type { Config, Context } from "@netlify/edge-functions";

export default async (req: Request, context: Context) => {
  const { country } = context.geo;
  if (country?.code === "DE") {
    return new URL("/de", req.url); // Rewrite to German page
  }
  // Return undefined to continue the chain
};

export const config: Config = {
  path: "/",
};

Key differences from serverless functions: Deno runtime (not Node.js), 50ms CPU limit, runs at edge (not a single region), return undefined to skip, return URL for same-site rewrite. Use context.next() to call the next function in the chain or the origin.

See examples/edge-functions.md for middleware patterns, geo-personalization, and response transformation.

---

Pattern 6: Netlify Blobs Storage

Blobs provide key-value storage accessible from functions and edge functions. No external database setup needed.

import { getStore } from "@netlify/blobs";
import type { Context } from "@netlify/functions";

export default async (req: Request, context: Context) => {
  const store = getStore("user-preferences");
  const userId = context.params.id;

  if (req.method === "GET") {
    const prefs = await store.get(userId, { type: "json" });
    if (!prefs) return new Response("Not found", { status: 404 });
    return Response.json(prefs);
  }

  if (req.method === "PUT") {
    const data = await req.json();
    await store.setJSON(userId, data);
    return new Response("Saved", { status: 200 });
  }
};

Consistency: Eventually consistent by default (~60s propagation). Use { consistency: "strong" } when immediate reads after writes are required.

See examples/edge-functions.md for Blobs patterns with metadata, listing, and deploy-scoped stores.

---

Pattern 7: Redirects and Rewrites

Redirects and rewrites are defined in netlify.toml with [[redirects]] tables. Status 200 creates a rewrite (URL stays the same). Status 301/302 creates a redirect.

# SPA fallback
[[redirects]]
  from = "/*"
  to = "/index.html"
  status = 200

# API proxy (avoids CORS)
[[redirects]]
  from = "/api/*"
  to = "https://api.example.com/:splat"
  status = 200
  force = true

# Old URL redirect
[[redirects]]
  from = "/old-blog/*"
  to = "/blog/:splat"
  status = 301

Key rules: Redirects are processed in order — first match wins. Use force = true to override existing files. Use :splat for wildcard captures and :paramName for named captures.

See reference.md for full redirect syntax, conditional redirects, and signed proxy patterns.

---

Pattern 8: Environment Variables

Environment variables are set in the Netlify UI (for secrets) or netlify.toml (for non-sensitive values). They support scopes (Builds, Functions) and deploy context overrides.

# netlify.toml — non-sensitive values only
[build.environment]
  NODE_VERSION = "20"

[context.production.environment]
  API_URL = "https://api.example.com"

[context.deploy-preview.environment]
  API_URL = "https://staging-api.example.com"

// In functions — always use Netlify.env, not process.env
const apiUrl = Netlify.env.get("API_URL");
const hasKey = Netlify.env.has("SECRET_KEY");

Key rule: Never put secrets in netlify.toml — it is version controlled. Use the Netlify UI or CLI (netlify env:set KEY value) for sensitive values.

---

Performance Optimization

Function Limits

Type	Execution Time	Memory	Payload Size
Serverless (sync)	60 seconds	1 GB	6 MB (request/response)
Serverless (streamed)	60 seconds	1 GB	20 MB (response)
Background	15 minutes	1 GB	256 KB
Scheduled	60 seconds	1 GB	N/A
Edge	50ms CPU	512 MB	N/A

Optimization Techniques

Technique	Impact
Response streaming	Faster TTFB, up to 20 MB response (vs 6 MB buffered)
context.waitUntil()	Returns response immediately, processes analytics/logging after
Edge functions with caching	Responses cached at edge, invocations don't count toward limits
esbuild bundler for functions	Faster builds than default zisi bundler
preferStatic: true on edge functions	Serves static files when available, skips edge function

Deploy Context Priority

Settings cascade from most general to most specific:

[build] (default for all contexts)
  └── [context.production] (production deploys)
  └── [context.deploy-preview] (PR/MR deploys)
  └── [context.branch-deploy] (non-production branches)
  └── [context."feature-branch"] (specific branch — highest priority)

---

<decision_framework>

Decision Framework

Choosing a Compute Primitive

What does your function need to do?
  |
  +-- API endpoint / webhook handler
  |     +-- Needs geo data or request transformation? --> Edge Function
  |     +-- Standard request/response? --> Serverless Function
  |
  +-- Scheduled/cron job
  |     +-- Under 60 seconds? --> Scheduled Function
  |     +-- Longer processing? --> Scheduled Function triggers Background Function
  |
  +-- Long-running task (data processing, batch operations)
  |     +-- Up to 15 minutes? --> Background Function
  |     +-- Longer? --> External service / queue
  |
  +-- Request modification (auth, geo-redirect, A/B test, headers)
        +-- Edge Function (runs before origin, at the nearest edge node)

Choosing Storage

What kind of data?
  |
  +-- Key-value pairs (preferences, config, cache)
  |     +-- Netlify Blobs (site-level store, eventual or strong consistency)
  |
  +-- Build artifacts / deploy-specific data
  |     +-- Netlify Blobs (deploy-scoped store)
  |
  +-- Relational data with queries
  |     +-- External database (PostgreSQL, MySQL, etc.)
  |
  +-- File uploads (images, documents)
        +-- Netlify Blobs (up to 5 GB per object)
        +-- External object storage for advanced needs

</decision_framework>

---

<red_flags>

RED FLAGS

High Priority Issues:

• Using process.env in modern Netlify functions — use Netlify.env.get() instead (process.env is unavailable in the modern runtime)
• Putting secrets in netlify.toml — this file is version controlled; use the Netlify UI or CLI for sensitive values
• Missing await on context.waitUntil() promises — work not passed to waitUntil may be silently cancelled after response
• Using .ts extension without "type": "module" in package.json — defaults to CommonJS, causing import issues; use .mts instead
• Scoping [[redirects]] or [[headers]] under [context.*] — they are always global and context scoping is silently ignored

Medium Priority Issues:

• Not setting force = true on proxy rewrites — without it, Netlify serves an existing file instead of proxying
• Using node_bundler = "zisi" (the default) instead of "esbuild" — esbuild is significantly faster
• Edge functions with /* path without preferStatic: true — shadows all static files, breaking CSS/JS/images
• Expecting edge functions to work with Split Testing — Split Testing relies on branch deploys which skip edge functions
• Not setting NODE_VERSION in build environment — defaults may not match your project's requirements

Common Mistakes:

• Trying to invoke scheduled functions via URL — they only run on their cron schedule (or manually via the Netlify UI)
• Expecting background functions to return data to the client — the client receives 202 immediately, return value is ignored
• Using context.next() in serverless functions — next() is an edge function concept for middleware chaining
• Forgetting that edge functions run on Deno, not Node.js — some Node.js APIs and npm packages may not be available
• Setting cookies across subdomains on netlify.app — netlify.app is on the Public Suffix List, cross-subdomain cookies require a custom domain

Gotchas & Edge Cases:

• Redirects are processed in order — first match wins; put specific rules before catch-all rules
• Edge function CPU time is 50ms, not wall-clock time — I/O waiting (fetch, Blobs) does not count
• Netlify Blobs is eventually consistent by default (~60s) — use { consistency: "strong" } for immediate reads after writes
• Deploy preview URLs have unique subdomains — hardcoded absolute URLs will break in previews; use relative paths
• The functions directory defaults to netlify/functions/ — custom paths need [functions] directory = "path" in netlify.toml
• Background functions have a 256 KB payload limit — much smaller than the 6 MB serverless limit
• Edge functions cannot rewrite to external URLs — use fetch() to retrieve external content and return it as a Response

</red_flags>

---

<critical_reminders>

CRITICAL REMINDERS

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST use Netlify.env.get() to access environment variables in functions — NOT process.env which is unavailable in the modern functions runtime)

(You MUST use the .mts file extension for serverless functions to get ES module support — .ts defaults to CommonJS unless "type": "module" is in package.json)

(You MUST use context.waitUntil() for post-response background work — work not passed to waitUntil may be cancelled when the response is sent)

(You MUST keep redirects and headers in netlify.toml — they are global and NOT scoped to deploy contexts)

Failure to follow these rules will cause broken environment variable access, module format errors, lost background work, and silently ignored configuration.

</critical_reminders>