Wrangler "compatibility_date" Missing or Invalid - Fix Workers Deploy

Cloudflare Workers pins runtime behavior to a compatibility_date. Wrangler errored because the date is missing from wrangler.toml, set in the future, or a needed compatibility_flags entry is absent.

What this error means

wrangler deploy/dev fails or warns about compatibility_date - missing, in the future, or required for a feature you use. It is deterministic: the same config fails the same way until the date/flags are corrected.

✘ [ERROR] A compatibility_date is required when publishing. Add the following to
your wrangler.toml:
```
compatibility_date = "2026-06-25"
```

Common causes

Missing or future compatibility_date

Without compatibility_date, Wrangler refuses to publish. A date in the future is also rejected because the runtime cannot honor behavior that has not shipped.

Required compatibility flag not set

Some runtime features (e.g. nodejs_compat) need an explicit flag in addition to the date; without it, APIs your code relies on are unavailable.

How to fix it

Set a valid compatibility_date and flags

Pin a real (non-future) date and add any flags your Worker needs.

# wrangler.toml
name = "my-worker"
main = "src/index.ts"
compatibility_date = "2026-06-25"
compatibility_flags = ["nodejs_compat"]

Verify the config locally

1. Run npx wrangler dev to confirm the runtime accepts the date and flags.
2. Bump compatibility_date deliberately when adopting new runtime behavior, and test after.
3. Keep the date no later than today - a future date is rejected.

How to prevent it

• Always set compatibility_date in wrangler.toml and keep it current but not in the future.
• Add required compatibility_flags (e.g. nodejs_compat) for the APIs you use.
• Test runtime behavior with wrangler dev after changing the date or flags.

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