Little Warden is one of those tools that, once you start using it, you'll wonder how you ever coped without it. Perfect for agencies handling many accounts.

Words cannot begin to express my gratitude that @littlewardenapp exists and saves my client sites from major incidents again and again. Worth every damn penny ten times over and then some.

If you work in SEO (particularly if you work on multiple clients), you should really give @littlewardenapp a go. Monitors various technical SEO aspects that you'd much rather not check manually. Only been using it for around a month and already benefited massively.