---
title: Compatibility Dates
description: Configure compatibility dates and flags in Miniflare to match Cloudflare Workers runtime behavior.
image: https://edgetunnel-b2h.pages.dev/dev-products-preview.png
---

> Documentation Index  
> Fetch the complete documentation index at: https://edgetunnel-b2h.pages.dev/workers/llms.txt  
> Use this file to discover all available pages before exploring further. 

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# Compatibility Dates

* [Compatibility Dates Reference](https://edgetunnel-b2h.pages.dev/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.

**JavaScript**

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

## Compatibility Flags

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

**JavaScript**

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

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```