Check your configuration before restarting from Settings > Tools > YAML > Check configuration. Home Assistant validates the YAML and configuration structure, then displays errors or warnings without applying your edits. Fix every reported problem and run the check again. If the check passes, reload the affected integration when a reload control is available; restart only when the change requires it or cannot be reloaded.
For command-line workflows, use ha core check on Home Assistant OS or hass --script check_config with Home Assistant Core. These commands are installation-specific, so do not substitute one for the other.
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What a configuration check does—and does not do
A configuration check is a pre-application test. It parses Home Assistant YAML files and checks configuration structures for problems that would prevent a valid load. The result tells you whether Home Assistant considers the configuration valid and, when it does not, identifies errors or warnings to investigate.
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The check does not apply the edited configuration. Your saved file can pass validation while the running instance continues using the previous configuration until you reload a supported integration or restart Home Assistant. This separation lets you find syntax and structure errors before a bad edit interrupts the service.
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Validation also cannot prove that an automation will behave correctly with live devices, changing entity states, network services, or timing conditions. A syntactically valid trigger, condition, or action can still implement the wrong logic. Treat the check as a safety gate before applying a change, not as a simulation of the automation.
Use the Home Assistant interface
The interface is the simplest option for administrators who edit YAML through the file editor, a network share, or another tool.
- Sign in with an administrator account.
- Open Settings > Tools > YAML. The Tools area is available to administrators. The exact page wording can vary between Home Assistant releases; some documentation refers to a Configuration validation or Check and restart area.
- Select Check configuration. Home Assistant reads the configuration files and reports whether they are valid.
- Read the complete result, including warnings. If an error is listed, return to the file, correct the indicated line or structure, save the file, and run Check configuration again.
- After a successful result, choose an applicable integration reload from the same YAML tools area. If no relevant reload exists, or the new behavior does not appear after reloading, restart Home Assistant.
The YAML tools page also exposes reload controls. A quick reload can reload all configuration, while individual controls target particular configuration areas. Use the narrowest reload that supports the change so unrelated integrations are not disturbed.
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Tools are restricted to administrators. If you cannot see the YAML tools, verify that the account has administrator rights and that you are in the current Settings interface rather than an older bookmark. Labels and placement can change between releases, so use the Settings search if the navigation text differs.
How to read the result
Valid
A valid result means Home Assistant accepted the YAML syntax and the configuration structures it checked. It does not activate the edit. Continue with an integration reload when supported, then verify the changed entity, helper, or automation in the running system.
Errors
An error prevents a safe apply. The message may identify a file, a line, a key, or a malformed structure. Correct the earliest reported problem first: one indentation mistake can cause many later messages because the parser no longer sees the intended hierarchy. Save the file and repeat the check rather than trying to apply a partially corrected configuration.
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Warnings
A warning is not necessarily a parse failure, but it signals a condition that may be deprecated, ambiguous, or risky. Read the wording and decide whether to change the configuration. In command-line workflows you can make warnings fail the check with the Core script’s --fail-on-warnings option.
Command-line validation by installation type
Home Assistant documents different commands for Home Assistant OS and Home Assistant Core. Identify the installation type before running a command.
| Installation or method | Command or path | What it provides | Important limitation |
|---|---|---|---|
| Home Assistant OS | ha core check |
A more comprehensive check of YAML files and configuration structures. | This is the OS command; it is not the documented command for a standalone Home Assistant Core installation. |
| Home Assistant Core | hass --script check_config |
Tests changes before launch without restarting Home Assistant. | Run it in the environment where the Core executable is installed and confirm options for that installed version. |
| Automation or script | homeassistant.check_config action |
Validates files without loading or applying the changes; reports through a persistent notification and logs. | Only administrators can run the action. |
| REST client | POST /api/config/core/check_config |
Returns a valid result on success or an invalid result with error details. | The config integration must be enabled; the endpoint is intended for programmatic workflows. |
Home Assistant OS: ha core check
Open the Home Assistant OS command-line interface and run:
ha core checkThe Home Assistant OS task documentation describes this as a comprehensive validation of YAML files and configuration structures. It is useful when you are already administering the host from a terminal or when the web interface is unavailable.
Home Assistant Core: hass --script check_config
For a Home Assistant Core installation, run:
hass --script check_configThe check_config script is designed to test changes without restarting Home Assistant. It supports options for non-default setups:
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Option names and behavior can vary with the installed version. Run hass --script check_config -h on the machine that will execute the check to see the available switches before incorporating the command into a deployment script.
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Trigger a check from an automation or script
Home Assistant exposes a homeassistant.check_config action for administrators who want validation inside an automation or script workflow. The action reads and validates the configuration files without loading or applying the edits. If it finds errors, Home Assistant creates a persistent notification and writes details to the logs.
This is useful when a maintenance automation needs to signal that a configuration file is unsafe before another step proceeds. It is not a replacement for testing the automation’s live behavior, and it does not reload or restart Home Assistant for you. Keep the validation action separate from any action that applies a reload or restart so an invalid result cannot accidentally continue the deployment sequence.
Use the REST API for programmatic checks
Programmatic clients can call the documented endpoint:
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POST /api/config/core/check_configThe request takes no additional request data. With the config integration enabled, Home Assistant returns a valid result when the configuration passes or an invalid result containing error details when it fails. Authentication and the normal REST API access controls still apply.
Most users should choose the UI or the command appropriate to their installation. The endpoint becomes practical when an external editor, deployment job, or monitoring process needs a machine-readable pass/fail result. Treat the response as a gate: stop the apply step on an invalid result, show the returned details to the operator, and run the check again after the file is corrected.
YAML problems the validator commonly exposes
Indentation and hierarchy
YAML uses indentation to express nesting. A key placed at the wrong level can make a valid-looking file fail to parse or create a structure Home Assistant does not accept. Keep indentation consistent and inspect the lines immediately above the reported location. If a parser reports an error several lines after your edit, check the preceding list marker, colon, and indentation first.
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For example, a list item must remain aligned with its siblings:
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trigger:
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entity_id: binary_sensor.hallway_motion
Adding or removing spaces before trigger or its list item changes the hierarchy. The check can identify the resulting syntax or configuration-structure problem, but it cannot infer which indentation you intended.
Values such as on and off
YAML can interpret unquoted words such as on and off as booleans. When the value is meant to be a literal state string, quote it:
to: 'on'
from: 'off'This matters in state-based automations and templates where the literal state is compared with an entity value. Quoting the state removes the ambiguity described in Home Assistant’s YAML syntax guidance.
Entity ID capitalization
Entity IDs are lowercase. A reference such as binary_sensor.Front_Door does not match binary_sensor.front_door. Correct the ID in the automation, script, dashboard, or service data, then run the configuration check again. Validation may not catch every semantically wrong reference, so confirm the final ID in Developer Tools or the entity registry as well.
Structure versus behavior
The validator can reject an unsupported key, malformed list, or invalid configuration structure. It cannot determine whether a valid structure expresses your intended sequence. After applying a passing edit, inspect traces, logs, entity states, and the relevant device response to verify behavior under the conditions that matter.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Check, reload, or restart?
Home Assistant states that most integrations using configuration.yaml can reload their configuration without a full restart. The YAML tools area presents reloads for individual configuration areas, plus a quick reload option for all configuration. Select the relevant reload when it exists.
Reload the affected configuration when
- The edited integration appears among the available reload controls.
- The change belongs to a configuration area documented as reloadable.
- You have confirmed the check passes and want to apply only that area.
Restart when
- No applicable reload control exists for the edited configuration.
- The integration’s reload completed but the change did not take effect.
- The specific change requires startup processing.
A full restart interrupts running automations and scripts. Plan it for a suitable time, especially when the system controls alarms, locks, heating, lighting, or other time-sensitive devices. A restart is an apply operation, not an additional substitute for checking; validate first.
A safe edit-to-apply workflow
- Identify the scope. Note which YAML file, integration, automation, or script you changed and whether that area has a reload control.
- Save the edit. Make sure the file on disk is the file Home Assistant reads. Unsaved editor buffers and edits to the wrong configuration directory will not be tested.
- Run the appropriate check. Use Settings > Tools > YAML > Check configuration,
ha core checkon Home Assistant OS, orhass --script check_configfor Home Assistant Core. - Resolve errors first. Start with the first parser or structure error, save, and check again. Treat warnings deliberately rather than ignoring them.
- Confirm a clean result. Keep the successful output or command status if the change is part of a repeatable maintenance process.
- Apply narrowly. Reload the affected configuration area when supported. Use a quick reload only when you intentionally want all configuration reloaded.
- Verify live behavior. Check entity states, automation traces, logs, and device responses. A passing configuration check is not a behavioral test.
- Restart only if required. If no reload is available or the edit remains unapplied, schedule a restart and verify the system after it returns.
Troubleshooting failed checks
The same error remains after editing
Confirm that you saved the file Home Assistant is actually using. For Core, run the check with the correct --config directory when the configuration is not in the default location. The --files option can show which files the script used. In the UI, reopen the file or use the editor’s saved-state indicator before checking again.
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Fix the earliest reported syntax or indentation issue and check again. YAML parsing often loses the intended hierarchy at the first misplaced space, causing subsequent lines to be reported as separate errors.
The check passes but the automation does nothing
Apply the change through the supported reload or restart workflow, then inspect the automation’s trigger, conditions, entity IDs, and trace. Confirm that the referenced entities exist with lowercase IDs and that the live state matches the value you used. Validation establishes loadability, not that a trigger will occur or an action will succeed.
A reload is not listed
Use a restart only after the configuration check passes. If a reload control is absent, Home Assistant may require startup processing for that configuration area. If a listed reload does not apply the edit, restart and then verify the result.
You need warnings to stop a deployment
For Home Assistant Core, add --fail-on-warnings to hass --script check_config. This makes the command return a non-zero result when warnings are present, allowing a script or CI job to halt before applying the change.
Quick Recap
Official references
- Home Assistant check_config documentation explains the Core script and its options.
- The configuration.yaml file documents checking, reloading, and restarting behavior.
- Common tasks for Home Assistant Operating System documents
ha core check. - Home Assistant Tools describes the YAML tools interface and reload controls.
- Testing automations recommends checking YAML syntax before restarting.
- The homeassistant.check_config action documents validation from automations and scripts.
- Home Assistant REST API documentation lists the configuration-check endpoint.
- Home Assistant YAML syntax covers indentation, quoted values, and related syntax details.
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