Wrangler Binding Undefined at Runtime - Fix Workers Bindings
A Worker tried to use a binding (env.MY_KV, env.DB, a secret) that is not configured. The binding is missing from wrangler.toml, declared only for another environment, or the underlying resource was never created.
What this error means
The Worker throws because env.<BINDING> is undefined, or wrangler deploy fails resolving a binding. It is deterministic: the binding is absent for the environment being deployed until it is declared and the resource exists.
TypeError: Cannot read properties of undefined (reading 'get')
at fetch (src/index.ts:8) - env.MY_KV is undefined
# or
✘ [ERROR] KV namespace 'MY_KV' is not defined for environment "production"Common causes
Binding not declared (or only for another env)
The [[kv_namespaces]] / [[r2_buckets]] / [[d1_databases]] block is missing, or defined under [env.staging] but not [env.production], so the deployed env has no binding.
Underlying resource not created
The binding references a namespace/bucket/database id that does not exist (never created, or a wrong id), so it cannot resolve at deploy/runtime.
How to fix it
Declare the binding for the right environment
Add the binding block, including under each named environment that needs it.
# wrangler.toml
[[kv_namespaces]]
binding = "MY_KV"
id = "abc123def456"
[env.production]
[[env.production.kv_namespaces]]
binding = "MY_KV"
id = "abc123def456"Create the resource and use its id
- Create the resource (e.g.
wrangler kv namespace create MY_KV) and copy the returned id. - Reference that exact id in the binding block.
- For secrets, set them with
wrangler secret put NAMEper environment.
How to prevent it
- Declare every binding in
wrangler.toml, including under each named environment. - Create the underlying resources and reference their real ids.
- Set secrets per environment with
wrangler secret put.