npx wrangler kv key put greeting "Hello world" --namespace-id 2f1b3c4d5e6f7a8b9c0d1e2f3a4b5c6d

Stores the value Hello world under the key greeting in the namespace. The key and value are positional; the value can be any string up to 25 MiB. Keys propagate to Cloudflare's global edge within seconds. For file contents as the value, use --path instead.