Four Kitchens

How to build a custom Alexa skill powered by Home Assistant

7 Min. ReadDevelopment

This post was originally published on Taylor’s personal website.

Using Home Assistant’s built-in Alexa integration, I can ask Alexa about my 3D printer or for a better weather report.

On a scale of 1 to 10, I currently rate my “Alexa Skill” skills at a whopping “learning to put LEGOs together.” My home automation setup is built using Home Assistant (my configuration on GitHub). One of the many components it integrates with is the Amazon Echo.

It offers two styles: integration via the Home Skills API for switching my lights and powering custom commands via the Skills API. I’ve set up both as documented on the component page.

For my first foray into custom commands, I wanted Alexa to be able to tell me about the status of 3D printing jobs. Seemed simple enough. Let’s walk through it.

Part 1 deals with the 3D printer integration, but Parts 2 through 4 pair up the two services and can be used for any information or command. My code samples include a custom weather report, too.

Part 1: Home Assistant’s OctoPrint component

For this, I’ll need Hass to monitor the OctoPrint instance that runs my printer. This part is easy, and done in three parts:

  1. Set up the “OctoPrint Hub” component, which just provides the API access and authentication.
  2. Set up the “OctoPrint Binary Sensor,” which gives simple “yes/no” answers about status, which makes crafting the status message easier.
  3. Set up the “OctoPrint Sensor,” which gives more detailed information as numbers and strings.

Bonus: setting up the camera feed so the Home Assistant window can show you the print surface is also pretty simple.

Replace with the IP address or hostname of your OctoPrint server.

# Step 1:
  api_key: !secret octoprint_api

# Step 2:
  - platform: octoprint
      - Printing
      - Printing Error

# Step 3:
  - platform: octoprint
    name: OctoPrint
      - Current State
      - Temperatures
      - Job Percentage

# Bonus, if you have a webcam on your OctoPi
  - platform: mjpeg
    name: Printer Camera

Links to relevant parts of my configuration: OctoPrint Hubthe binary senorsregular sensors, and webcam.

Now that Home Assistant knows the metrics we want to use, it needs to be reachable from the Internet.

Part 2: Allowing connections from AWS to Home Assistant

Set an HTTP API password. Repeat after me: set an API password.

Also, the Alexa Skills API will only connect to HTTPS endpoints.

# In the root of configuration.yaml
  api_password: !secret http_password
  ssl_certificate: /home/hass/.homeassistant/cert.pem
  ssl_key: /home/hass/.homeassistant/key.pem

# In secrets.yaml
http_password: NowIKnowMyABCs

Next, I generated a self-signed certificate with this command. You can provide a cert file to AWS to skip SSL validation, so self-signed certs for personal-use skills are sufficient.

openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 3650 -nodes

Finally, open and forward your router’s external port 443 to your Hass server on the port that it actually runs on. Note: understand the possible ramifications of this before you do it. Do not expose internal resources to external traffic unless you understand these risks.

Restart Home Assistant for the new OctoPrint integration and SSL configuration. Remember, using a self-signed certificate will cause you to have an SSL warning in your browser.

Part 3: The Home Assistant Skill configuration

Home Assistant has an Alexa Skills API component out of the box, all we need to do is configure the Hass side of the skill we’re building. In this example, we’ll use the newly configured OctoPrint sensors to announce the 3D printer status.

      type: plaintext
      text: >
        The printer is {{ states("sensor.octoprint_current_state") | lower }}
        {% if is_state("binary_sensor.octoprint_printing", "on") %}
          and the job is {{ states("sensor.octoprint_job_percentage") | round }} percent complete
        {% else %}
          and not currently printing
        {% endif %}.

This sets up a simple response to the PrinterStatusIntent intent using Home Assistant’s templating engine. Remember that intent name, we’ll use it again on the Amazon configuration. The response reads something like:

“The printer is printing and the job is 80% complete.”

Or, if the printer isn’t printing but Home Assistant and OctoPrint are connected:

“The printer is operational and not currently printing.”

My Alexa configuration file.

Once this is saved, restart Home Assistant and you’ll have the Alexa skill response ready to test from Amazon. The skill will not appear in the Hass UI.

Part 4: Alexa Skills configuration

Home Assistant’s Alexa Component documentation outlines the steps required. It’s pretty straightforward, though slightly outdated. Here’s a picture guide as of March 2017. (Amazon changes this frequently, I gather.)

  • Click “Alexa” in the top navigation bar, then “Get Started” under “Alexa Skills Kit”
  • Click “Add a new skill” in the top right

Next, we’ll set up the skill basics:

  • For Skill Type keep “Custom Interaction Model” selected.
  • The Name is the skill name as shown in the Alexa app and the Developer Console; it’s an administrative title.
  • The Invocation Name is the skill you request verbally, e.g. “Alexa, ask Hathi for…”. (All my computers are named for Jungle Book characters; Colonel Hathi is the elephant leader.)

Then click next to configure the intents, or the things Home Assistant can do. Each intent has a name, and slots for variables to pass to the skill.

Remember the Intent name we used above? Repeat that here to link this up to the Home Assistant configuration: PrinterStatusIntent

  "intents": [
      "intent": "PrinterStatusIntent"

The “utterances” are the things a user can say to trigger the intent, after the “Alexa, ask Invocation Name.” This becomes “Alexa, ask Hathi for the printer status,” or “Alexa, ask Hathi about the printer.”

PrinterStatusIntent printer status
PrinterStatusIntent about the printer

Then click next to work through the endpoint configuration:

  • For Endpoint, I selected “HTTPS.” It’s easy to hook up an AWS Lambda resource, but since Home Assistant has an Alexa API built-in, it was easier to have AWS connect directly.
  • Select the sensible region for your endpoint.
  • Enter your endpoint URL in the displayed field: https://YOUR_HOST/api/alexa?api_password=YOUR_API_PASSWORD
  • Do not enable Account Linking. That’s if AWS would need account-specific data, like Spotify or YNAB skills. Home Assistant doesn’t have user accounts.

Next up is SSL configuration:

If you created an SSL certificate in Part 1 above, copy the whole text of the .pem file into this text field:

[[ ... A dozen or two more lines like this ... ]]

Click next for the testing options, the final step required to make this skill run for personal use.

On this page, you can send a test request and see the full exchange between Home Assistant and Amazon:

If everything goes according to plan, you’ll see and hear one of the responses explained above.

Save the project and follow the instructions to enable the skill on your own account and give it a shot:

I once won an Oscar for my cell phone steady-cam skills…

Wrapping up

All in, this took me less than two hours to set up because documentation on both sides is extensive, though having experience with AWS is helpful. Having this framework to extend means I could get Alexa to tell me anything from Home Assistant or execute commands not compatible with Home Skills. Check out my Hass Alexa config for another example that pulls a weather report.

From a user experience perspective, I think saying the “invocation name” is a hindrance. Except for built-in skills, everything you ask Alexa to do must include “ask/tell Service Name…” I don’t know the solution to this problem, but ultimately it feels like similar UX issues of discoverability that emerge in hidden navigation and gesture-heavy interfaces: you have to already know how to use it. No guest could walk into my place and intuit how to get info from Home Assistant.

There’s promise though, the Home Skills API doesn’t need a separate invocation name for its services (though you should pick obvious names for devices), and Amazon has noticed this issue. In late 2016, they announced an initiative to create a new built-in library of intents and slots and easier ways to trigger them. A preview of this library has already been released for US developers.