Durable Objects

What it does

When your agent uses it

• Tasks that involve Agent memory

Example prompts

• “/durable-objects”

Workflow steps

7 steps, taken from the first numbered list in SKILL.md.

1. 1Model around coordination atoms - One DO per chat room/game/user, not one global DO
2. 2Use getByName() for deterministic routing - Same input = same DO instance
3. 3Use SQLite storage - Configure new_sqlite_classes in migrations
4. 4Initialize in constructor - Use blockConcurrencyWhile() for schema setup only
5. 5Use RPC methods - Not fetch() handler (compatibility date >= 2024-04-03)
6. 6Persist first, cache second - Always write to storage before updating in-memory state
7. 7One alarm per DO - setAlarm() replaces any existing alarm

What it can do on your machine

Read from SKILL.md and the folder at commit 41e0d19. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  No scripts in the folder and no shell commands in SKILL.md (its code samples are typescript and jsonc).

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • developers.cloudflare.com

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Durable Objects loads about 1.5k tokens when it runs, and up to ~4.7k if it reads all its reference files. Until then it costs about 28 tokens; SKILL.md has 395 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~28

When it runs · the whole SKILL.md, loaded when a task matches

~1.5k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~4.7k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from cloudflare/skills at commit 41e0d19, republished under its Apache-2.0 licence (© cloudflare). 395 words, ~1,510 tokens.

name

durable-objects

description

Build, debug, or review Cloudflare Durable Objects code for persistent state and coordination.

// wrangler.jsonc
{
  "durable_objects": {
    "bindings": [{ "name": "MY_DO", "class_name": "MyDurableObject" }]
  },
  "migrations": [{ "tag": "v1", "new_sqlite_classes": ["MyDurableObject"] }]
}

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 });
  },
};

// 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);

// 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");

// 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();

© cloudflare, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 3 other files (references) in skills/durable-objects of cloudflare/skills.

• SKILL.md
• references/rules.md
• references/testing.md
• references/workers.md

Open the folder on GitHubat commit 41e0d19

Used in 2 other repositories

We found 2 copies of this SKILL.md (exact, near-identical or edited) in other folders, from 2 other GitHub owners. This page covers the copy in cloudflare/skills, which our catalogue first saw on October 7, 2026.

• softmaple/softmaple.agents/skills/durable-objects
• fcakyon/claude-codex-settingsplugins/cloudflare-skills/skills/durable-objects