---
description: Configure compatibility dates and flags in Miniflare to match Cloudflare Workers runtime behavior.
title: Compatibility Dates
image: https://developers.cloudflare.com/og-docs.png
---

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# Compatibility Dates

Last updated Aug 25, 2026|Copy as Markdown|[View as Markdown](https://4f1c5cd2.previews.developers.cloudflare.com/workers/testing/miniflare/core/compatibility/index.md)|[Agent setup](https://4f1c5cd2.previews.developers.cloudflare.com/agent-setup/)

* [Compatibility Dates Reference](https://4f1c5cd2.previews.developers.cloudflare.com/workers/configuration/compatibility-dates)

## Compatibility Dates

Miniflare uses compatibility dates to opt-into backwards-incompatible changes from a specific date. If one isn't set, it will default to some time far in the past.

```js
const mf = new Miniflare({
	compatibilityDate: "2021-11-12",
});
```

## Compatibility Flags

Miniflare also lets you opt-in/out of specific changes using compatibility flags:

```js
const mf = new Miniflare({
	compatibilityFlags: [
		"formdata_parser_supports_files",
		"durable_object_fetch_allows_relative_url",
	],
});
```

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