What this actually solves
The changelog entry, from cloudflare/workers-sdk’s packages/wrangler/CHANGELOG.md, wrangler@4.115.0 (released 2026-07-28):
“Add experimental
local_dev.experimental_s3_credentialstor2_bucketsconfig”
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.
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.
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
{
"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 archive.
