Fix a Home Assistant YAML problem by first identifying the failure class: YAML parsing, Home Assistant configuration validation, automation schema/setup, or template rendering. Read the exact log message, confirm the configuration directory and file being loaded, correct only the offending structure or value, run a configuration check, and then reload the affected configuration or restart if a reload is unavailable.
The same-looking “YAML error” can have very different causes. A tab produces a parser failure, while a valid YAML document with an unsupported automation key produces a schema error. A template may parse successfully but fail later when it is rendered. Treating those as separate cases prevents trial-and-error edits and unnecessary restarts.
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How do I fix common Home Assistant YAML configuration errors?
Use this sequence whenever Home Assistant reports a YAML-related problem:
- Copy the complete error, including the file name, line number, and message detail.
- Open Settings > System > Logs and look for warnings or errors from the integration, automation, script, or template involved.
- Confirm the configuration directory used by the running installation. Home Assistant reports that directory during startup; editing a similarly named file elsewhere will not change the active system.
- Classify the failure as a YAML parser error, a Home Assistant schema/configuration error, an integration setup error, or a template-rendering error.
- Make the smallest correction, run a configuration check, and only then reload or restart.
Home Assistant’s YAML syntax documentation notes that most things can be configured directly in the interface, so YAML is not required for every task. It remains useful for integrations and advanced features, but a careful validation workflow is safer than repeatedly restarting after unverified edits.
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Identify which kind of failure you have
YAML parser errors
A parser error means the file cannot be read as YAML at all. Typical messages include found character 't' that cannot start any token and could not find expected ':'. The line reported by the parser, and often the line immediately above it, is the best place to start. Check indentation, colons, quotation marks, brackets, and list markers.
Home Assistant configuration or schema errors
Here the YAML is syntactically valid, but a key, value, or nesting level is not accepted by Home Assistant. Automation editors commonly report Message malformed: followed by a detail naming the invalid trigger, condition, or action option. Correct YAML can still fail this validation because Home Assistant expects a particular schema.
Integration setup failures
An integration may parse its YAML and then fail while setting itself up. Logs usually identify the integration and provide a more specific reason, such as an unavailable device, an invalid option, or a connection problem. Do not keep changing indentation when the log has already moved past YAML parsing.
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Template-rendering errors
A template can be valid YAML and valid Home Assistant configuration but fail when it is evaluated. Undefined variables, misspelled entity IDs, invalid operators, and filters that return an unexpected type are common causes. The template editor and the template error message usually point to the expression that failed.
Capture the exact message and active file first
Open Settings > System > Logs and expand the relevant warning or error. Copy the complete text rather than paraphrasing it; a phrase such as Message malformed is only useful when the following detail is included. If an integration offers diagnostics, download them from its integration page and keep the diagnostic file with the log entry while troubleshooting.
Confirm which configuration directory the running instance uses. A container, Home Assistant OS installation, and a supervised or manual installation can place files in different locations. Home Assistant reports the active directory during startup. If you edit a file outside that directory, your correction will never be seen by the process you are checking.
Check whether the problem began after editing configuration.yaml, an included file such as automations.yaml, a package, or a template file. Includes can make the error appear to belong to the parent file even though the invalid line is in a child file. Work outward from the exact path and line shown in the log.
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Correct the YAML syntax traps that cause most failures
Replace tabs with spaces
YAML indentation must use spaces. The parser message found character 't' that cannot start any token means a tab was used where YAML expects indentation or content. Configure your editor to insert spaces, show invisible characters, and convert existing indentation tabs to spaces. Do not mix tabs and spaces in one block.
automation:
- alias: Turn on hallway light
trigger:
- platform: state
entity_id: binary_sensor.hallway_motionThe visual width of a tab varies by editor, so code that looks aligned on screen can still be invalid. Re-indent the affected mapping from its parent key rather than inserting spaces until it merely appears to line up.
Preserve indentation and the space after a colon
Indentation expresses the parent-child relationship in YAML. A missing space after a colon, an item aligned with the wrong parent, or a list marker at the wrong level can produce a parser error or silently create a different data structure.
sensor:
- platform: mqtt
name: Kitchen temperature
state_topic: house/kitchen/temperatureIn this example, platform, name, and state_topic belong to the same list item. Moving one of them left or right changes the structure. When a parser points at a line that looks correct, inspect the preceding indentation and the nearest list marker.
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Do not duplicate a top-level section
A configuration file cannot safely contain multiple top-level sections with the same name. For example, two separate automation: sections can cause one mapping to overwrite another or fail validation, depending on how the file is loaded. Combine entries under one section or use the documented include and platform arrangement for multiple sources. The same principle applies to other repeated top-level keys.
Quote state values that YAML may reinterpret
YAML interprets words such as true, Yes, ON, and off as boolean-like values in common YAML parsers. If you mean the literal Home Assistant state string, quote it.
condition:
- condition: state
entity_id: input_boolean.guest_mode
state: 'on'Leaving on or off unquoted can lead to an error such as not a valid value for dictionary value @ data, because the integration receives a boolean instead of the expected string. Quote other values when their spelling could be interpreted as a number, boolean, or special YAML value.
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Use the exact, lowercase entity ID
Home Assistant is case-sensitive. Entity IDs use lowercase characters, so binary_sensor.Front_Door does not refer to binary_sensor.front_door. Go to Settings > Developer Tools > States (shown as Settings > Tools > States in some interface versions) and copy the entity ID from the state list. Also verify that the entity still exists after an integration rename or device replacement.
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Home Assistant configuration files must be UTF-8 encoded. If the log reports a UTF-8 decoding error, reopen the affected file in an editor that lets you choose the encoding and save it as UTF-8. Avoid silently adding a different legacy encoding when transferring files between operating systems.
Fix Jinja templates embedded in YAML
Quote a single-line template
YAML can interpret an unquoted {{ or {% as flow-style syntax. Quote a single-line template so the whole expression is treated as a scalar value.
value_template: "{{ states('sensor.temp') | float > 20 }}"This quoting rule is separate from the quotes inside the Jinja expression. The outer YAML quotes protect the template from the YAML parser; the inner single quotes delimit the entity ID passed to states().
Use a block scalar for multiline templates
For a template that spans multiple lines, use a YAML block scalar and indent every template line beneath it.
message: >
The temperature is {{ states('sensor.temp') | float(0) }} degrees.
The fan is {{ states('fan.living_room') }}.> folds line breaks into spaces. Use | instead when preserving line breaks is important, such as a formatted notification. The block indicator must be aligned with the key, and the template content must be indented farther than that key.
Resolve errors that occur only when the template runs
- Undefined or unavailable value: check spelling and provide a fallback, such as
states('sensor.temp') | float(0), when an entity may be unavailable. - Misspelled variable: compare every variable with the names supplied by the integration or the surrounding template context.
- Wrong data type: filters such as
mapandselectreturn iterables. Add| listbefore counting, indexing, or using a list-specific operation when the resulting type requires it. - Syntax error: inspect the reported line for missing punctuation, unmatched parentheses, an incorrect filter separator, or an operator that Jinja does not support.
A template-rendering failure is not fixed by changing unrelated YAML indentation. Test the expression in the template editor when available, then return it to the configuration file with the correct YAML quoting or block-scalar indentation.
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Run a configuration check before restarting
Always validate after editing. Home Assistant checks configuration when you reload configuration or restart, but performing an explicit check first prevents an avoidable outage and shows errors before automations are interrupted.
Use the interface
For automation YAML workflows, open Settings > Tools > YAML > Check configuration. The check reports whether the configuration is valid and lists errors or warnings. Interface labels can vary slightly by release, so look for the YAML configuration-check action under the Tools page if the wording differs.
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Use the command line
From the Home Assistant installation environment, run:
hass --script check_configThe documented script accepts options for different troubleshooting situations:
-cspecifies the configuration directory when it is not the default.-fshows the configuration files that are used, which helps reveal an unexpected include path.--jsonformats the result as JSON for scripts or log processing.--fail-on-warningsreturns a nonzero status when warnings should stop an automated deployment.
Run the command in the environment where Home Assistant is installed. Running it on a host that does not contain the active configuration directory checks the wrong files and can give a misleading result.
Use the homeassistant.check_config action
The homeassistant.check_config action reads and validates configuration files without loading them. It creates a persistent notification and writes details to the logs when errors are found. Calling this action requires administrator rights, so expose it only to trusted users and automation contexts.
Choose the right diagnostic method
| Method | Best use | Where or effect |
|---|---|---|
| Logs and integration diagnostics | Warnings, setup failures, and integration-specific details | Settings > System > Logs; download diagnostics when the integration offers them |
| YAML configuration check in the UI | Pre-restart validation from the browser | Settings > Tools > YAML > Check configuration; displays errors and warnings |
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Command-line validation with an explicit directory and output controls | Runs in the Home Assistant installation environment without a restart |
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Validation initiated by an automation or script | Reads files without loading them; requires administrator rights and reports through a notification and logs |
| Reload | Applying supported YAML changes | Reloads the affected integration or domain without a full process restart |
| Restart | Applying a change when reload is unavailable or did not take effect | Restarts Home Assistant and interrupts running automations and scripts |
Resolve automation-specific errors
Read the detail after “Message malformed”
When saving an automation produces Message malformed:, the text that follows identifies the invalid part. It may name a trigger, condition, action, or option. Correct that key or value and save again; do not replace the entire automation with an unrelated example before understanding the detail.
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A message that explicitly mentions YAML, indentation, or spacing indicates a parser problem instead. Fix the file structure first, then address any schema error that appears after the file can be parsed.
Remove legacy keys when a current key is present
Automation syntax has evolved. An automation that contains both an old key and its current replacement can be rejected or interpreted ambiguously. Keep one form and move its items under that form. Examples documented by Home Assistant include:
trigger:versustriggers:platform:versustrigger:service:versusaction:
Do not paste a current example beneath an older example while leaving both keys in place. After removing the legacy key, run the configuration check again so the next error, if any, is isolated.
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Automations created in the user interface are commonly stored in automations.yaml. If they disappear after an edit, confirm that configuration.yaml still contains:
automation: !include automations.yamlIf the include was deleted or changed, restore it, check the configuration, and reload automations. Restart only when the reload does not apply the corrected include or when the affected change cannot be reloaded.
Check list and mapping levels
Triggers, conditions, and actions are commonly lists. A misplaced dash can turn a list into a mapping or attach an item to the wrong section. Compare the indentation of each dash with the key that owns it, and ensure every nested option is indented consistently beneath its trigger, condition, or action.
Reload first; restart only when necessary
Many integrations that use YAML support a reload. Use the domain-specific reload after a successful configuration check so the changed file is applied without stopping the entire Home Assistant process. A reload does not help if the integration does not support it, if the include path is wrong, or if the change affects startup-only settings.
If the corrected configuration still does not apply, restart Home Assistant. A restart interrupts automations and scripts, so choose a safe time and expect in-progress actions to stop. Check the logs immediately after startup; a successful restart does not prove that every automation or integration loaded correctly.
A practical decision tree for recurring errors
The error names a tab or token
- Open the exact file and line.
- Show invisible characters in the editor.
- Replace tabs with spaces and re-indent the whole mapping.
- Run the configuration check before reloading.
The error says a value is invalid
- Determine whether YAML converted the value to a boolean or number.
- Quote literal state strings such as
'on'or'off'. - Check spelling, allowed options, and the expected nesting for that integration.
- Run the check again and use the new detail if validation advances to another field.
The automation editor reports “Message malformed”
- Read the complete detail after the colon.
- Verify the trigger, condition, or action schema.
- Remove duplicate old and current keys.
- Confirm that file-based automations are included from
configuration.yaml. - Save, check configuration, and reload automations.
The file checks but a template fails
- Move the expression into the template editor, if available.
- Check entity IDs, variable names, punctuation, and operators.
- Convert iterables to a list when a later operation needs one.
- Add a safe fallback for unavailable states.
- Quote a single-line template or use a correctly indented block scalar.
The check passes but the change is not visible
- Confirm that you edited the active configuration directory.
- Use the
-foption with the command-line checker to inspect included files. - Verify that the relevant domain supports reload and reload that domain.
- Restart only if reload is unsupported or the setting is startup-only.
- Inspect post-reload or post-restart logs for an integration setup failure separate from YAML syntax.
Prevent the next YAML failure
- Keep editor indentation set to spaces and enable visible whitespace.
- Make one logical change at a time, then run a configuration check.
- Copy entity IDs from the States tool instead of typing them.
- Quote values whose meaning depends on being a literal string.
- Keep templates short; move complex multiline expressions into clearly indented block scalars.
- Remove obsolete automation keys when adopting a newer documented form.
- Record the active configuration directory and include structure so you know which file Home Assistant loads.
- Use reloads for supported domains and plan for automation interruption before a restart.
There is no published Home Assistant statistic establishing how frequently YAML errors occur. The reliable, documented remedies are therefore the concrete checks above: read the logs, distinguish parsing from validation and rendering, validate before restarting, and apply the narrowest safe reload or restart.
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