--- description: Set up Wrangler bindings, Durable Objects, and container settings for Sandbox SDK. title: Wrangler configuration image: https://developers.cloudflare.com/og-docs.png --- [Skip to content](#main-content) > Documentation Index > Fetch the complete documentation index at: https://developers.cloudflare.com/sandbox/llms.txt > Use this file to discover all available pages before exploring further. # Wrangler configuration Last updated Aug 24, 2026|Copy as Markdown|[View as Markdown](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/configuration/wrangler/index.md)|[Agent setup](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/agent-setup/) ## Minimal configuration The minimum required configuration for using Sandbox SDK: ```jsonc { "name": "my-sandbox-worker", "main": "src/index.ts", // Set this to today's date "compatibility_date": "2026-08-24", "compatibility_flags": ["nodejs_compat"], "containers": [ { "class_name": "Sandbox", "image": "./Dockerfile", }, ], "durable_objects": { "bindings": [ { "class_name": "Sandbox", "name": "Sandbox", }, ], }, "migrations": [ { "new_sqlite_classes": ["Sandbox"], "tag": "v1", }, ], } ``` ```toml name = "my-sandbox-worker" main = "src/index.ts" # Set this to today's date compatibility_date = "2026-08-24" compatibility_flags = [ "nodejs_compat" ] [[containers]] class_name = "Sandbox" image = "./Dockerfile" [[durable_objects.bindings]] class_name = "Sandbox" name = "Sandbox" [[migrations]] new_sqlite_classes = [ "Sandbox" ] tag = "v1" ``` ## Required settings The Sandbox SDK is built on Cloudflare Containers. Your configuration requires three sections: 1. **containers** \- Define the container image (your runtime environment) 2. **durable\_objects.bindings** \- Bind the Sandbox Durable Object to your Worker 3. **migrations** \- Initialize the Durable Object class The minimal configuration shown above includes all required settings. For detailed configuration options, refer to the [Containers configuration documentation](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/wrangler/configuration/#containers). ## Backup storage To use the [backup and restore API](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/api/backups/), you need an R2 bucket binding and presigned URL credentials. The container uploads and downloads backup archives directly to/from R2 using presigned URLs, which requires R2 API token credentials. ### 1\. Create the R2 bucket ```sh npx wrangler r2 bucket create my-backup-bucket ``` ### 2\. Add the binding and environment variables ```jsonc { "vars": { "BACKUP_BUCKET_NAME": "my-backup-bucket", "CLOUDFLARE_ACCOUNT_ID": "", }, "r2_buckets": [ { "binding": "BACKUP_BUCKET", "bucket_name": "my-backup-bucket", }, ], } ``` ```toml [vars] BACKUP_BUCKET_NAME = "my-backup-bucket" CLOUDFLARE_ACCOUNT_ID = "" [[r2_buckets]] binding = "BACKUP_BUCKET" bucket_name = "my-backup-bucket" ``` ### 3\. Set R2 API credentials as secrets ```sh npx wrangler secret put R2_ACCESS_KEY_ID npx wrangler secret put R2_SECRET_ACCESS_KEY ``` Create an R2 API token in the [Cloudflare dashboard ↗](https://dash.cloudflare.com/) under **R2** \> **Overview** \> **Manage R2 API Tokens**. The token needs **Object Read & Write** permissions for your backup bucket. The SDK uses these credentials to generate presigned URLs that allow the container to transfer backup archives directly to and from R2\. For a complete setup walkthrough, refer to the [backup and restore guide](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/guides/backup-restore/). ## Troubleshooting ### Binding not found **Error**: `TypeError: env.Sandbox is undefined` **Solution**: Ensure your `wrangler.jsonc` includes the Durable Objects binding: ```jsonc { "durable_objects": { "bindings": [ { "class_name": "Sandbox", "name": "Sandbox", }, ], }, } ``` ```toml [[durable_objects.bindings]] class_name = "Sandbox" name = "Sandbox" ``` ### Missing migrations **Error**: Durable Object not initialized **Solution**: Add migrations for the Sandbox class: ```jsonc { "migrations": [ { "new_sqlite_classes": ["Sandbox"], "tag": "v1", }, ], } ``` ```toml [[migrations]] new_sqlite_classes = [ "Sandbox" ] tag = "v1" ``` ## Related resources * [Deploy a Sandbox application](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/guides/deploy/) \- Deploy and keep package and image aligned * [Deploy Containers](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/containers/deploy/) \- Containers deploy path * [Transport modes](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/configuration/transport/) \- Configure HTTP, WebSocket, and RPC transport * [Wrangler documentation](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/workers/wrangler/) \- Complete Wrangler reference * [Durable Objects setup](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/durable-objects/get-started/) \- DO-specific configuration * [Dockerfile reference](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/configuration/dockerfile/) \- Custom container images * [Environment variables](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/configuration/environment-variables/) \- Passing configuration to sandboxes * [Get Started guide](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/get-started/) \- Initial setup walkthrough Was this helpful? YesNo ## On this page [![](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/_astro/logo.te5VL_aD.svg)Docs](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/) ```json {"@context":"https://schema.org","@type":"TechArticle","@id":"https://developers.cloudflare.com/sandbox/configuration/wrangler/#page","headline":"Wrangler configuration · Cloudflare Sandbox SDK docs","description":"Set up Wrangler bindings, Durable Objects, and container settings for Sandbox SDK.","url":"https://developers.cloudflare.com/sandbox/configuration/wrangler/","inLanguage":"en","image":"https://developers.cloudflare.com/og-docs.png","dateModified":"2026-08-24","publisher":{"@type":"Organization","name":"Cloudflare","description":"One platform for your apps, agents, and workforce. Build, secure, and scale without managing infrastructure","url":"https://www.cloudflare.com/","sameAs":["https://github.com/cloudflare","https://www.linkedin.com/company/cloudflare","https://x.com/cloudflare"],"logo":{"@type":"ImageObject","url":"https://developers.cloudflare.com/logo.svg"},"address":{"@type":"PostalAddress","streetAddress":"101 Townsend St","addressLocality":"San Francisco","addressRegion":"CA","postalCode":"94107","addressCountry":"US"},"contactPoint":[{"@type":"ContactPoint","contactType":"Customer Support","url":"https://support.cloudflare.com/","availableLanguage":["English"]},{"@type":"ContactPoint","contactType":"Sales","url":"https://www.cloudflare.com/contact/","availableLanguage":["English"]}]},"isPartOf":{"@type":"WebSite","@id":"https://developers.cloudflare.com/#website","name":"Cloudflare Docs","url":"https://developers.cloudflare.com/"}} ```