Rules

Below the list of rules supported by Biome, divided by group. Here’s a legend of the emojis:

The icon indicates that the rule is part of the recommended rules.
The icon indicates that the rule provides a code action (fix) that is safe to apply.
The icon indicates that the rule provides a code action (fix) that is unsafe to apply.
The icon indicates that the rule is applied to JavaScript and super languages files.
The icon indicates that the rule is applied to TypeScript and TSX files.
The icon indicates that the rule is applied to JSON files.
The icon indicates that the rule is applied to CSS files.
The icon indicates that the rule is applied to GraphQL files.

Accessibility

Rules focused on preventing accessibility problems.

Rule name	Description	Properties
noAccessKey	Enforce that the attribute is not used on any HTML element.
noAriaHiddenOnFocusable	Enforce that aria-hidden=“true” is not set on focusable elements.
noAriaUnsupportedElements	Enforce that elements that do not support ARIA roles, states, and properties do not have those attributes.
noAutofocus	Enforce that autoFocus prop is not used on elements.
noBlankTarget	Disallow attribute without
noDistractingElements	Enforces that no distracting elements are used.
noHeaderScope	The scope prop should be used only on elements.
noInteractiveElementToNoninteractiveRole	Enforce that non-interactive ARIA roles are not assigned to interactive HTML elements.
noNoninteractiveElementToInteractiveRole	Enforce that interactive ARIA roles are not assigned to non-interactive HTML elements.
noNoninteractiveTabindex	Enforce that is not assigned to non-interactive HTML elements.
noPositiveTabindex	Prevent the usage of positive integers on property
noRedundantAlt	Enforce alt prop does not contain the word “image”, “picture”, or “photo”.
noRedundantRoles	Enforce explicit property is not the same as implicit/default role property on an element.
noSvgWithoutTitle	Enforces the usage of the element for the element.
useAltText	Enforce that all elements that require alternative text have meaningful information to relay back to the end user.
useAnchorContent	Enforce that anchors have content and that the content is accessible to screen readers.
useAriaActivedescendantWithTabindex	Enforce that is assigned to non-interactive HTML elements with .
useAriaPropsForRole	Enforce that elements with ARIA roles must have all required ARIA attributes for that role.
useButtonType	Enforces the usage of the attribute for the element
useHeadingContent	Enforce that heading elements (h1, h2, etc.) have content and that the content is accessible to screen readers. Accessible means that it is not hidden using the aria-hidden prop.
useHtmlLang	Enforce that element has attribute.
useIframeTitle	Enforces the usage of the attribute for the element .
useKeyWithClickEvents	Enforce onClick is accompanied by at least one of the following: , , .
useKeyWithMouseEvents	Enforce / are accompanied by / .
useMediaCaption	Enforces that and elements must have a for captions.
useValidAnchor	Enforce that all anchors are valid, and they are navigable elements.
useValidAriaProps	Ensures that ARIA properties are all valid.
useValidAriaRole	Elements with ARIA roles must use a valid, non-abstract ARIA role.
useValidAriaValues	Enforce that ARIA state and property values are valid.
useValidLang	Ensure that the attribute passed to the attribute is a correct ISO language and/or country.

Complexity

Rules that focus on inspecting complex code that could be simplified.

Rule name	Description	Properties
noBannedTypes	Disallow primitive type aliases and misleading types.
noEmptyTypeParameters	Disallow empty type parameters in type aliases and interfaces.
noExcessiveCognitiveComplexity	Disallow functions that exceed a given Cognitive Complexity score.
noExcessiveNestedTestSuites	This rule enforces a maximum depth to nested in test files.
noExtraBooleanCast	Disallow unnecessary boolean casts
noForEach	Prefer statement instead of .
noMultipleSpacesInRegularExpressionLiterals	Disallow unclear usage of consecutive space characters in regular expression literals
noStaticOnlyClass	This rule reports when a class has no non-static members, such as for a class used exclusively as a static namespace.
noThisInStatic	Disallow and in contexts.
noUselessCatch	Disallow unnecessary clauses.
noUselessConstructor	Disallow unnecessary constructors.
noUselessEmptyExport	Disallow empty exports that don’t change anything in a module file.
noUselessFragments	Disallow unnecessary fragments
noUselessLabel	Disallow unnecessary labels.
noUselessLoneBlockStatements	Disallow unnecessary nested block statements.
noUselessRename	Disallow renaming import, export, and destructured assignments to the same name.
noUselessSwitchCase	Disallow useless in statements.
noUselessTernary	Disallow ternary operators when simpler alternatives exist.
noUselessThisAlias	Disallow useless aliasing.
noUselessTypeConstraint	Disallow using or as type constraint.
noVoid	Disallow the use of operators, which is not a familiar operator.
noWith	Disallow statements in non-strict contexts.
useArrowFunction	Use arrow functions over function expressions.
useFlatMap	Promotes the use of when are used together.
useLiteralKeys	Enforce the usage of a literal access to properties over computed property access.
useOptionalChain	Enforce using concise optional chain instead of chained logical expressions.
useRegexLiterals	Enforce the use of the regular expression literals instead of the RegExp constructor if possible.
useSimpleNumberKeys	Disallow number literal object member names which are not base10 or uses underscore as separator
useSimplifiedLogicExpression	Discard redundant terms from logical expressions.

Correctness

Rules that detect code that is guaranteed to be incorrect or useless.

Rule name	Description	Properties
noChildrenProp	Prevent passing of children as props.
noConstAssign	Prevents from having variables being re-assigned.
noConstantCondition	Disallow constant expressions in conditions
noConstantMathMinMaxClamp	Disallow the use of and to clamp a value where the result itself is constant.
noConstructorReturn	Disallow returning a value from a .
noEmptyCharacterClassInRegex	Disallow empty character classes in regular expression literals.
noEmptyPattern	Disallows empty destructuring patterns.
noFlatMapIdentity	Disallow to use unnecessary callback on .
noGlobalObjectCalls	Disallow calling global object properties as functions
noInnerDeclarations	Disallow and declarations that are accessible outside their block.
noInvalidConstructorSuper	Prevents the incorrect use of inside classes. It also checks whether a call is missing from classes that extends other constructors.
noInvalidNewBuiltin	Disallow operators with global non-constructor functions.
noInvalidUseBeforeDeclaration	Disallow the use of variables and function parameters before their declaration
noNewSymbol	Disallow operators with the object.
noNodejsModules	Forbid the use of Node.js builtin modules.
noNonoctalDecimalEscape	Disallow and escape sequences in string literals.
noPrecisionLoss	Disallow literal numbers that lose precision
noRenderReturnValue	Prevent the usage of the return value of .
noSelfAssign	Disallow assignments where both sides are exactly the same.
noSetterReturn	Disallow returning a value from a setter
noStringCaseMismatch	Disallow comparison of expressions modifying the string case with non-compliant value.
noSwitchDeclarations	Disallow lexical declarations in clauses.
noUndeclaredVariables	Prevents the usage of variables that haven’t been declared inside the document.
noUnnecessaryContinue	Avoid using unnecessary .
noUnreachable	Disallow unreachable code
noUnreachableSuper	Ensures the constructor is called exactly once on every code path in a class constructor before is accessed if the class has a superclass
noUnsafeFinally	Disallow control flow statements in finally blocks.
noUnsafeOptionalChaining	Disallow the use of optional chaining in contexts where the undefined value is not allowed.
noUnusedImports	Disallow unused imports.
noUnusedLabels	Disallow unused labels.
noUnusedPrivateClassMembers	Disallow unused private class members
noUnusedVariables	Disallow unused variables.
noVoidElementsWithChildren	This rules prevents void elements (AKA self-closing elements) from having children.
noVoidTypeReturn	Disallow returning a value from a function with the return type ‘void’
useArrayLiterals	Disallow Array constructors.
useExhaustiveDependencies	Enforce all dependencies are correctly specified in a React hook.
useHookAtTopLevel	Enforce that all React hooks are being called from the Top Level component functions.
useIsNan	Require calls to when checking for .
useJsxKeyInIterable	Disallow missing key props in iterators/collection literals.
useValidForDirection	Enforce “for” loop update clause moving the counter in the right direction.
useYield	Require generator functions to contain .

Nursery

New rules that are still under development.

Nursery rules require explicit opt-in via configuration on stable versions because they may still have bugs or performance problems.
They are enabled by default on nightly builds, but as they are unstable their diagnostic severity may be set to either error or
warning, depending on whether we intend for the rule to be recommended or not when it eventually gets stabilized.
Nursery rules get promoted to other groups once they become stable or may be removed.

Rules that belong to this group are not subject to semantic version.

Rule name	Description	Properties
noConsole	Disallow the use of .
noDoneCallback	Disallow using a callback in asynchronous tests and hooks.
noDuplicateAtImportRules	Disallow duplicate rules.
noDuplicateElseIf	Disallow duplicate conditions in if-else-if chains
noDuplicateFontNames	Disallow duplicate names within font families.
noDuplicateSelectorsKeyframeBlock	Disallow duplicate selectors within keyframe blocks.
noEmptyBlock	Disallow CSS empty blocks.
noEvolvingTypes	Disallow variables from evolving into type through reassignments.
noImportantInKeyframe	Disallow invalid within keyframe declarations
noInvalidPositionAtImportRule	Disallow the use of at-rules in invalid positions.
noLabelWithoutControl	Enforce that a label element or component has a text label and an associated input.
noMisplacedAssertion	Checks that the assertion function, for example , is placed inside an function call.
noReactSpecificProps	Prevents React-specific JSX properties from being used.
noRestrictedImports	Disallow specified modules when loaded by import or require.
noUndeclaredDependencies	Disallow the use of dependencies that aren’t specified in the .
noUnknownFunction	Disallow unknown CSS value functions.
noUnknownMediaFeatureName	Disallow unknown media feature names.
noUnknownProperty	Disallow unknown properties.
noUnknownPseudoElement	Disallow unknown pseudo-element selectors.
noUnknownUnit	Disallow unknown CSS units.
noUnmatchableAnbSelector	Disallow unmatchable An+B selectors.
noUnusedFunctionParameters	Disallow unused function parameters.
noUselessStringConcat	Disallow unnecessary concatenation of string or template literals.
noUselessUndefinedInitialization	Disallow initializing variables to .
noValueAtRule	Disallow use of rule in css modules.
noYodaExpression	Disallow the use of yoda expressions.
useAdjacentOverloadSignatures	Disallow the use of overload signatures that are not next to each other.
useConsistentBuiltinInstantiation	Enforce the use of for all builtins, except , , , and .
useDateNow	Use to get the number of milliseconds since the Unix Epoch.
useDefaultSwitchClause	Require the default clause in switch statements.
useErrorMessage	Enforce passing a message value when creating a built-in error.
useExplicitLengthCheck	Enforce explicitly comparing the , , or property of a value.
useFocusableInteractive	Elements with an interactive role and interaction handlers must be focusable.
useGenericFontNames	Disallow a missing generic family keyword within font families.
useImportExtensions	Enforce file extensions for relative imports.
useImportRestrictions	Disallows package private imports.
useNumberToFixedDigitsArgument	Enforce using the digits argument with .
useSemanticElements	It detects the use of attributes in JSX elements and suggests using semantic elements instead.
useSortedClasses	Enforce the sorting of CSS utility classes.
useStrictMode	Enforce the use of the directive in script files.
useThrowNewError	Require when throwing an error.
useThrowOnlyError	Disallow throwing non- values.
useTopLevelRegex	Require regex literals to be declared at the top level.

Performance

Rules catching ways your code could be written to run faster, or generally be more efficient.

Rule name	Description	Properties
noAccumulatingSpread	Disallow the use of spread () syntax on accumulators.
noBarrelFile	Disallow the use of barrel file.
noDelete	Disallow the use of the operator.
noReExportAll	Avoid re-export all.

Security

Rules that detect potential security flaws.

Rule name	Description	Properties
noDangerouslySetInnerHtml	Prevent the usage of dangerous JSX props
noDangerouslySetInnerHtmlWithChildren	Report when a DOM element or a component uses both and prop.
noGlobalEval	Disallow the use of global .

Style

Rules enforcing a consistent and idiomatic way of writing your code.

Rule name	Description	Properties
noArguments	Disallow the use of .
noCommaOperator	Disallow comma operator.
noDefaultExport	Disallow default exports.
noImplicitBoolean	Disallow implicit values on JSX boolean attributes
noInferrableTypes	Disallow type annotations for variables, parameters, and class properties initialized with a literal expression.
noNamespace	Disallow the use of TypeScript’s s.
noNamespaceImport	Disallow the use of namespace imports.
noNegationElse	Disallow negation in the condition of an statement if it has an clause.
noNonNullAssertion	Disallow non-null assertions using the postfix operator.
noParameterAssign	Disallow reassigning parameters.
noParameterProperties	Disallow the use of parameter properties in class constructors.
noRestrictedGlobals	This rule allows you to specify global variable names that you don’t want to use in your application.
noShoutyConstants	Disallow the use of constants which its value is the upper-case version of its name.
noUnusedTemplateLiteral	Disallow template literals if interpolation and special-character handling are not needed
noUselessElse	Disallow block when the block breaks early.
noVar	Disallow the use of
useAsConstAssertion	Enforce the use of over literal type and type annotation.
useBlockStatements	Requires following curly brace conventions.
useCollapsedElseIf	Enforce using instead of nested in clauses.
useConsistentArrayType	Require consistently using either or
useConst	Require declarations for variables that are only assigned once.
useDefaultParameterLast	Enforce default function parameters and optional function parameters to be last.
useEnumInitializers	Require that each enum member value be explicitly initialized.
useExponentiationOperator	Disallow the use of in favor of the operator.
useExportType	Promotes the use of for types.
useFilenamingConvention	Enforce naming conventions for JavaScript and TypeScript filenames.
useForOf	This rule recommends a loop when in a loop, the index used to extract an item from the iterated array.
useFragmentSyntax	This rule enforces the use of over .
useImportType	Promotes the use of for types.
useLiteralEnumMembers	Require all enum members to be literal values.
useNamingConvention	Enforce naming conventions for everything across a codebase.
useNodeAssertStrict	Promotes the usage of over .
useNodejsImportProtocol	Enforces using the protocol for Node.js builtin modules.
useNumberNamespace	Use the properties instead of global ones.
useNumericLiterals	Disallow and in favor of binary, octal, and hexadecimal literals
useSelfClosingElements	Prevent extra closing tags for components without children
useShorthandArrayType	When expressing array types, this rule promotes the usage of shorthand instead of .
useShorthandAssign	Require assignment operator shorthand where possible.
useShorthandFunctionType	Enforce using function types instead of object type with call signatures.
useSingleCaseStatement	Enforces switch clauses have a single statement, emits a quick fix wrapping the statements in a block.
useSingleVarDeclarator	Disallow multiple variable declarations in the same variable statement
useTemplate	Prefer template literals over string concatenation.
useWhile	Enforce the use of loops instead of loops when the initializer and update expressions are not needed.

Suspicious

Rules that detect code that is likely to be incorrect or useless.

Rule name	Description	Properties
noApproximativeNumericConstant	Use standard constants instead of approximated literals.
noArrayIndexKey	Discourage the usage of Array index in keys.
noAssignInExpressions	Disallow assignments in expressions.
noAsyncPromiseExecutor	Disallows using an async function as a Promise executor.
noCatchAssign	Disallow reassigning exceptions in catch clauses.
noClassAssign	Disallow reassigning class members.
noCommentText	Prevent comments from being inserted as text nodes
noCompareNegZero	Disallow comparing against
noConfusingLabels	Disallow labeled statements that are not loops.
noConfusingVoidType	Disallow type outside of generic or return types.
noConsoleLog	Disallow the use of
noConstEnum	Disallow TypeScript
noControlCharactersInRegex	Prevents from having control characters and some escape sequences that match control characters in regular expressions.
noDebugger	Disallow the use of
noDoubleEquals	Require the use of and .
noDuplicateCase	Disallow duplicate case labels.
noDuplicateClassMembers	Disallow duplicate class members.
noDuplicateJsxProps	Prevents JSX properties to be assigned multiple times.
noDuplicateObjectKeys	Disallow two keys with the same name inside objects.
noDuplicateObjectKeys	Disallow two keys with the same name inside objects.
noDuplicateParameters	Disallow duplicate function parameter name.
noDuplicateTestHooks	A block should not contain duplicate hooks.
noEmptyBlockStatements	Disallow empty block statements and static blocks.
noEmptyInterface	Disallow the declaration of empty interfaces.
noExplicitAny	Disallow the type usage.
noExportsInTest	Disallow using or in files containing tests
noExtraNonNullAssertion	Prevents the wrong usage of the non-null assertion operator () in TypeScript files.
noFallthroughSwitchClause	Disallow fallthrough of clauses.
noFocusedTests	Disallow focused tests.
noFunctionAssign	Disallow reassigning function declarations.
noGlobalAssign	Disallow assignments to native objects and read-only global variables.
noGlobalIsFinite	Use instead of global .
noGlobalIsNan	Use instead of global .
noImplicitAnyLet	Disallow use of implicit type on variable declarations.
noImportAssign	Disallow assigning to imported bindings
noLabelVar	Disallow labels that share a name with a variable
noMisleadingCharacterClass	Disallow characters made with multiple code points in character class syntax.
noMisleadingInstantiator	Enforce proper usage of and .
noMisrefactoredShorthandAssign	Disallow shorthand assign when variable appears on both sides.
noPrototypeBuiltins	Disallow direct use of builtins.
noRedeclare	Disallow variable, function, class, and type redeclarations in the same scope.
noRedundantUseStrict	Prevents from having redundant .
noSelfCompare	Disallow comparisons where both sides are exactly the same.
noShadowRestrictedNames	Disallow identifiers from shadowing restricted names.
noSkippedTests	Disallow disabled tests.
noSparseArray	Disallow sparse arrays
noSuspiciousSemicolonInJsx	It detects possible “wrong” semicolons inside JSX elements.
noThenProperty	Disallow property.
noUnsafeDeclarationMerging	Disallow unsafe declaration merging between interfaces and classes.
noUnsafeNegation	Disallow using unsafe negation.
useAwait	Ensure functions utilize .
useDefaultSwitchClauseLast	Enforce default clauses in switch statements to be last
useGetterReturn	Enforce methods to always return a value.
useIsArray	Use instead of .
useNamespaceKeyword	Require using the keyword over the keyword to declare TypeScript namespaces.
useValidTypeof	This rule verifies the result of unary expressions is being compared to valid values, either string literals containing valid type names or other expressions

Recommended rules

The recommended rules are: