---
title: New r2_buckets Local Dev Credentials in Wrangler
description: Wrangler 4.115 adds local_dev.experimental_s3_credentials to r2_buckets bindings, scoping real S3-compatible credentials to local dev instead of faking R2.
date: 2026-08-06T00:00:00.000Z
category: dev-tools
tags: wrangler, cloudflare-workers, r2, local-dev
---

## Quick Answer

`wrangler@4.115.0` adds an experimental `local_dev.experimental_s3_credentials` field to `r2_buckets` bindings, letting a project supply real S3-compatible credentials scoped specifically to local development. Before this, local R2 testing either used Miniflare's built-in simulated store or had no clean way to point at a real S3-compatible endpoint without touching production-adjacent credentials.

## What this actually solves

The changelog entry, from `cloudflare/workers-sdk`'s `packages/wrangler/CHANGELOG.md`, [`wrangler@4.115.0`](https://github.com/cloudflare/workers-sdk/releases/tag/wrangler%404.115.0) (released 2026-07-28):

> "Add experimental `local_dev.experimental_s3_credentials` to `r2_buckets` config"

R2's Workers API is S3-compatible, and Miniflare's default local dev experience simulates an R2 bucket without needing any credentials at all. That default is fine for most local testing, but it isn't a real S3-compatible endpoint, so any local test that genuinely needs S3-specific behavior, not just an R2 binding's basic get/put/list surface, had no first-class way to supply real credentials scoped just to that local session.

<Callout type="warning" title="The field name itself has already changed once">
  This configuration key was originally shipped as a flat
  `experimental_local_s3_credentials` field, then moved to the current nested
  `local_dev.experimental_s3_credentials` shape (tracked across
  `cloudflare/workers-sdk` pull requests #14119 and #14280). It's marked
  experimental for a reason: confirm the current field name and its exact
  sub-fields against `wrangler r2 bucket --help` or the current Cloudflare R2
  docs before copying a config block from anywhere, including this post.
</Callout>

## Structural Comparison Matrix

| Operational Aspect                      | Before (v4.114.0 and earlier)                      | After (v4.115.0+)                                         |
| :-------------------------------------- | :------------------------------------------------- | :-------------------------------------------------------- |
| **Default local R2**                    | Miniflare's simulated store, no credentials needed | Unchanged, still the default                              |
| **Real S3-compatible endpoint locally** | No first-class config field                        | `local_dev.experimental_s3_credentials` on the binding    |
| **Credential scope**                    | N/A                                                | Scoped to local dev, separate from production credentials |

## Fix it: add the field to your local dev config

```jsonc title="wrangler.jsonc (shape as of wrangler@4.115.0+; verify exact sub-fields yourself)"
{
  "r2_buckets": [
    {
      "binding": "MY_BUCKET",
      "bucket_name": "my-bucket-name",
      "local_dev": {
        "experimental_s3_credentials": {
          // exact sub-field names are experimental and have already
          // changed once; confirm against `wrangler r2 bucket --help`
          // before filling this in
        },
      },
    },
  ],
}
```

If you don't need to test against a real S3-compatible endpoint locally, there's nothing to change. Miniflare's default simulated R2 store keeps working exactly as it did before this field existed.

## Confirmed version

Sourced from `cloudflare/workers-sdk`'s `packages/wrangler/CHANGELOG.md`, `wrangler@4.115.0`, released 2026-07-28, corroborated by the field-rename history tracked across pull requests #14119 and #14280. The exact sub-field shape wasn't independently reproduced here, since it's explicitly experimental and this site doesn't use R2 bindings; verify current syntax before adopting it. Browse more posts like this in the [Dev Tools](/dev-tools) archive.