Compatibility Dates

Last updated Apr 23, 2026 - Compatibility Dates Reference

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.

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

Compatibility Flags

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

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

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description: Dispatch and test HTTP fetch events in Miniflare for Cloudflare Workers. title: Fetch Events image: https://developers.cloudflare.com/workers/testing/miniflare/core/fetch/og.png?v=c552026745ff03e5

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