durable-objects
Build, debug, or review Cloudflare Durable Objects code for persistent state and coordination.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/cloudflare/skills --skill durable-objects- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads durable-objects automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
Security audits
Independent scans of the skill's instructions and bundled files.
SKILL.md
The instructions your agent reads when the skill is triggered.
Durable Objects
Build stateful, coordinated applications on Cloudflare's edge using Durable Objects.
Retrieval Sources
Your knowledge of Durable Objects APIs and configuration may be outdated. Prefer retrieval over pre-training for any Durable Objects task.
Fetch the relevant doc page when implementing features.
When to Use
- Creating new Durable Object classes for stateful coordination
- Implementing RPC methods, alarms, or WebSocket handlers
- Reviewing existing DO code for best practices
- Configuring wrangler.jsonc/toml for DO bindings and migrations
- Writing tests with Cloudflare’s Vitest integration
- Designing sharding strategies and parent-child relationships
Reference Documentation
./references/rules.md- Core rules, storage, concurrency, RPC, alarms- Testing reference - Current Vitest documentation, migration choices, and test selection
./references/workers.md- Workers handlers, types, wrangler config, observability
Search: blockConcurrencyWhile, idFromName, getByName, setAlarm, sql.exec
Core Principles
Use Durable Objects For
| Need | Example |
|---|---|
| Coordination | Chat rooms, multiplayer games, collaborative docs |
| Strong consistency | Inventory, booking systems, turn-based games |
| Per-entity storage | Multi-tenant SaaS, per-user data |
| Persistent connections | WebSockets, real-time notifications |
| Scheduled work per entity | Subscription renewals, game timeouts |
Do NOT Use For
- Stateless request handling (use plain Workers)
- Maximum global distribution needs
- High fan-out independent requests
Quick Reference
Wrangler Configuration
// wrangler.jsonc
{
"durable_objects": {
"bindings": [{ "name": "MY_DO", "class_name": "MyDurableObject" }]
},
"migrations": [{ "tag": "v1", "new_sqlite_classes": ["MyDurableObject"] }]
}
Basic Durable Object Pattern
import { DurableObject } from "cloudflare:workers";
export interface Env {
MY_DO: DurableObjectNamespace<MyDurableObject>;
}
export class MyDurableObject extends DurableObject<Env> {
constructor(ctx: DurableObjectState, env: Env) {
super(ctx, env);
ctx.blockConcurrencyWhile(async () => {
this.ctx.storage.sql.exec(`
CREATE TABLE IF NOT EXISTS items (
id INTEGER PRIMARY KEY AUTOINCREMENT,
data TEXT NOT NULL
)
`);
});
}
async addItem(data: string): Promise<number> {
const result = this.ctx.storage.sql.exec<{ id: number }>(
"INSERT INTO items (data) VALUES (?) RETURNING id",
data
);
return result.one().id;
}
}
export default {
async fetch(request: Request, env: Env): Promise<Response> {
const stub = env.MY_DO.getByName("my-instance");
const id = await stub.addItem("hello");
return Response.json({ id });
},
};
Critical Rules
- Model around coordination atoms - One DO per chat room/game/user, not one global DO
- Use
getByName()for deterministic routing - Same input = same DO instance - Use SQLite storage - Configure
new_sqlite_classesin migrations - Initialize in constructor - Use
blockConcurrencyWhile()for schema setup only - Use RPC methods - Not fetch() handler (compatibility date >= 2024-04-03)
- Persist first, cache second - Always write to storage before updating in-memory state
- One alarm per DO -
setAlarm()replaces any existing alarm
Authorization
Durable Objects do not have separate roles or permissions; access follows the Worker that implements them. Retrieve the current Durable Objects authorization guidance before granting observability or Data Studio access, and scope the Workers role to the intended Worker or Workers product.
Anti-Patterns (NEVER)
- Single global DO handling all requests (bottleneck)
- Using
blockConcurrencyWhile()on every request (kills throughput) - Storing critical state only in memory (lost on eviction/crash)
- Using
awaitbetween related storage writes (breaks atomicity) - Holding
blockConcurrencyWhile()acrossfetch()or external I/O
Stub Creation
// Deterministic - preferred for most cases
const stub = env.MY_DO.getByName("room-123");
// From existing ID string
const id = env.MY_DO.idFromString(storedIdString);
const stub = env.MY_DO.get(id);
// New unique ID - store mapping externally
const id = env.MY_DO.newUniqueId();
const stub = env.MY_DO.get(id);
Storage Operations
// SQL (synchronous, recommended)
this.ctx.storage.sql.exec("INSERT INTO t (c) VALUES (?)", value);
const rows = this.ctx.storage.sql.exec<Row>("SELECT * FROM t").toArray();
// KV (async)
await this.ctx.storage.put("key", value);
const val = await this.ctx.storage.get<Type>("key");
Alarms
// Schedule (replaces existing)
await this.ctx.storage.setAlarm(Date.now() + 60_000);
// Handler
async alarm(): Promise<void> {
// Process scheduled work
// Optionally reschedule: await this.ctx.storage.setAlarm(...)
}
// Cancel
await this.ctx.storage.deleteAlarm();
Testing
Read the testing reference before configuring a suite or writing Durable Object tests. It routes to current setup, APIs, and examples and identifies the behavior to cover.
FAQ
What does the durable-objects skill do?
Build, debug, or review Cloudflare Durable Objects code for persistent state and coordination.
How do I install durable-objects?
Run npx skills add https://github.com/cloudflare/skills --skill durable-objects in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/durable-objects/ (personal) or .claude/skills/durable-objects/ (project).
Which AI agents can use durable-objects?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is durable-objects safe to install?
Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed; Runlayer passed; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.
Who maintains durable-objects?
It is published by cloudflare in cloudflare/skills, and it is an official skill from the maker of the technology it covers. It has 111,574 recorded installs.
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