# Helper services

Echo, HTMLService and other built-in services that come in handy during development.

The `zato.server.service.internal.helpers` module contains a set of helper services coming in handy during development and documented below.

The services can be used either standalone or as base classes for user-defined ones.

## Echo {#echo}

Echos 1:1 everything received on input. Usage idea - mounting on [a REST channel](https://zato.io/docs/dev/rest/channels.html) secured with credentials that need to be confirmed. If correct, response will be equal to request.

## HTMLService {#htmlservice}

Produces HTML output - described in [the frontend services chapter](https://zato.io/docs/dev/frontend/index.html).

## Helper API programming tools and techniques {#helper-api-programming-tools-and-techniques}

- [Date and time utilities](https://zato.io/docs/dev/datetime.html)
- [Helper services](https://zato.io/docs/dev/helpers.html)
- [How to invoker other Zato services](https://zato.io/docs/dev/invoking-services.html)
- [Distributed locks](https://zato.io/docs/dev/dist-locks.html)