Compatibility Dates

Understanding and managing Cloudflare compatibility dates

What Are Compatibility Dates?

The compatibility_date in wrangler.toml pins your Worker to a specific version of the Cloudflare Workers runtime. This prevents breaking changes from affecting your deployed code.

compatibility_date = "2024-12-01"

How They Work

• Cloudflare introduces runtime changes behind flags tied to dates
• Setting a date enables all changes up to and including that date
• Your code uses the same runtime behavior until you update the date
• New projects should use a recent date

When to Update

Update the compatibility date when:

• You are actively working on the project
• You want access to new runtime features
• The Cloudflare docs recommend a minimum date for a feature you need

Compatibility Flags

For granular control, you can enable or disable specific flags:

compatibility_date = "2024-12-01"
compatibility_flags = ["nodejs_compat"]

Common flags: