Rules

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

• The emoji ✅ indicates that the rule is part of the recommended rules.
• The emoji 🔧 indicates that the rule provides a code action (fix) that is safe to apply.
• The emoji ⚠️ indicates that the rule provides a code action (fix) that is unsafe to apply.

Accessibility

Section titled Accessibility

Rules focused on preventing accessibility problems.

Rule name	Description	Properties
noAccessKey	Enforce that the accessKey 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 target=“_blank” attribute without rel=“noreferrer”	✅ 🔧
noDistractingElements	Enforces that no distracting elements are used.	✅ ⚠️
noHeaderScope	The scope prop should be used only on <th> 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 tabIndex is not assigned to non-interactive HTML elements.	✅ ⚠️
noPositiveTabindex	Prevent the usage of positive integers on tabIndex property	✅ ⚠️
noRedundantAlt	Enforce img alt prop does not contain the word “image”, “picture”, or “photo”.	✅
noRedundantRoles	Enforce explicit role property is not the same as implicit/default role property on an element.	✅ ⚠️
noSvgWithoutTitle	Enforces the usage of the title element for the svg 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 tabIndex is assigned to non-interactive HTML elements with aria-activedescendant.	✅ ⚠️
useAriaPropsForRole	Enforce that elements with ARIA roles must have all required ARIA attributes for that role.	✅
useButtonType	Enforces the usage of the attribute type for the element button	✅
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 html element has lang attribute.	✅
useIframeTitle	Enforces the usage of the attribute title for the element iframe.	✅
useKeyWithClickEvents	Enforce onClick is accompanied by at least one of the following: onKeyUp, onKeyDown, onKeyPress.	✅
useKeyWithMouseEvents	Enforce onMouseOver / onMouseOut are accompanied by onFocus / onBlur.	✅
useMediaCaption	Enforces that audio and video elements must have a track for captions.	✅
useValidAnchor	Enforce that all anchors are valid, and they are navigable elements.	✅
useValidAriaProps	Ensures that ARIA properties aria-* 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 lang attribute is a correct ISO language and/or country.	✅

Complexity

Section titled Complexity

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

Rule name	Description	Properties
noBannedTypes	Disallow primitive type aliases and misleading types.	✅ 🔧
noExcessiveCognitiveComplexity	Disallow functions that exceed a given Cognitive Complexity score.
noExtraBooleanCast	Disallow unnecessary boolean casts	✅ ⚠️
noForEach	Prefer for…of statement instead of Array.forEach.	✅
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 this and super in static contexts.	✅ ⚠️
noUselessCatch	Disallow unnecessary catch 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.	✅ 🔧
noUselessRename	Disallow renaming import, export, and destructured assignments to the same name.	✅ 🔧
noUselessSwitchCase	Disallow useless case in switch statements.	✅ ⚠️
noUselessThisAlias	Disallow useless this aliasing.	✅ 🔧
noUselessTypeConstraint	Disallow using any or unknown as type constraint.	✅ 🔧
noVoid	Disallow the use of void operators, which is not a familiar operator.
noWith	Disallow with statements in non-strict contexts.	✅
useArrowFunction	Use arrow functions over function expressions.	✅ 🔧
useFlatMap	Promotes the use of .flatMap() when map().flat() 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

Section titled 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 const variables being re-assigned.	✅ ⚠️
noConstantCondition	Disallow constant expressions in conditions	✅
noConstructorReturn	Disallow returning a value from a constructor.	✅
noEmptyCharacterClassInRegex	Disallow empty character classes in regular expression literals.	✅
noEmptyPattern	Disallows empty destructuring patterns.	✅
noGlobalObjectCalls	Disallow calling global object properties as functions	✅
noInnerDeclarations	Disallow function and var declarations that are accessible outside their block.	✅
noInvalidConstructorSuper	Prevents the incorrect use of super() inside classes. It also checks whether a call super() is missing from classes that extends other constructors.	✅
noInvalidNewBuiltin	Disallow new operators with global non-constructor functions.	✅ ⚠️
noNewSymbol	Disallow new operators with the Symbol object.	⚠️
noNonoctalDecimalEscape	Disallow \8 and \9 escape sequences in string literals.	✅ ⚠️
noPrecisionLoss	Disallow literal numbers that lose precision	✅
noRenderReturnValue	Prevent the usage of the return value of React.render.	✅
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 switch clauses.	✅ ⚠️
noUndeclaredVariables	Prevents the usage of variables that haven’t been declared inside the document.
noUnnecessaryContinue	Avoid using unnecessary continue.	✅ ⚠️
noUnreachable	Disallow unreachable code	✅
noUnreachableSuper	Ensures the super() constructor is called exactly once on every code path in a class constructor before this 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.	✅
noUnusedLabels	Disallow unused labels.	✅ ⚠️
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’	✅
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 isNaN() when checking for NaN.	✅ ⚠️
useValidForDirection	Enforce “for” loop update clause moving the counter in the right direction.	✅
useYield	Require generator functions to contain yield.	✅

Performance

Section titled 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.	✅
noDelete	Disallow the use of the delete operator.	✅ ⚠️

Security

Section titled 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 children and dangerouslySetInnerHTML prop.	✅

Style

Section titled Style

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

Rule name	Description	Properties
noArguments	Disallow the use of arguments.	✅
noCommaOperator	Disallow comma operator.	✅
noDefaultExport	Disallow default exports.
noImplicitBoolean	Disallow implicit true 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 namespaces.
noNegationElse	Disallow negation in the condition of an if statement if it has an else clause.	🔧
noNonNullAssertion	Disallow non-null assertions using the ! postfix operator.	✅ ⚠️
noParameterAssign	Disallow reassigning function 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 else block when the if block breaks early.	✅ ⚠️
noVar	Disallow the use of var	✅ ⚠️
useAsConstAssertion	Enforce the use of as const over literal type and type annotation.	✅ 🔧
useBlockStatements	Requires following curly brace conventions.	⚠️
useCollapsedElseIf	Enforce using else if instead of nested if in else clauses.	🔧
useConst	Require const declarations for variables that are never reassigned after declared.	✅ 🔧
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 Math.pow in favor of the ** operator.	✅ ⚠️
useFragmentSyntax	This rule enforces the use of <>…</> over <Fragment>…</Fragment>.	⚠️
useLiteralEnumMembers	Require all enum members to be literal values.	✅
useNamingConvention	Enforce naming conventions for everything across a codebase.	🔧
useNumericLiterals	Disallow parseInt() and Number.parseInt() 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 T[] shorthand instead of Array<T>.	⚠️
useShorthandAssign	Require assignment operator shorthand where possible.	⚠️
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 while loops instead of for loops when the initializer and update expressions are not needed.	✅ 🔧

Suspicious

Section titled 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 -0	✅ 🔧
noConfusingLabels	Disallow labeled statements that are not loops.	✅
noConfusingVoidType	Disallow void type outside of generic or return types.	✅
noConsoleLog	Disallow the use of console.log	⚠️
noConstEnum	Disallow TypeScript const enum	✅ 🔧
noControlCharactersInRegex	Prevents from having control characters and some escape sequences that match control characters in regular expressions.	✅
noDebugger	Disallow the use of debugger	✅ ⚠️
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	Prevents object literals having more than one property declaration for the same name.	✅ ⚠️
noDuplicateParameters	Disallow duplicate function parameter name.	✅
noEmptyInterface	Disallow the declaration of empty interfaces.	✅ 🔧
noExplicitAny	Disallow the any type usage.	✅
noExtraNonNullAssertion	Prevents the wrong usage of the non-null assertion operator (!) in TypeScript files.	✅ 🔧
noFallthroughSwitchClause	Disallow fallthrough of switch clauses.	✅
noFunctionAssign	Disallow reassigning function declarations.	✅
noGlobalIsFinite	Use Number.isFinite instead of global isFinite.	✅ ⚠️
noGlobalIsNan	Use Number.isNaN instead of global isNaN.	✅ ⚠️
noImplicitAnyLet	Disallow use of implicit any type on variable declarations.	✅
noImportAssign	Disallow assigning to imported bindings	✅
noLabelVar	Disallow labels that share a name with a variable	✅
noMisleadingInstantiator	Enforce proper usage of new and constructor.	✅
noMisrefactoredShorthandAssign	Disallow shorthand assign when variable appears on both sides.	⚠️
noPrototypeBuiltins	Disallow direct use of Object.prototype builtins.	✅
noRedeclare	Disallow variable, function, class, and type redeclarations in the same scope.	✅
noRedundantUseStrict	Prevents from having redundant “use strict”.	✅ 🔧
noSelfCompare	Disallow comparisons where both sides are exactly the same.	✅
noShadowRestrictedNames	Disallow identifiers from shadowing restricted names.	✅
noSparseArray	Disallow sparse arrays	✅ ⚠️
noUnsafeDeclarationMerging	Disallow unsafe declaration merging between interfaces and classes.	✅
noUnsafeNegation	Disallow using unsafe negation.	✅ ⚠️
useDefaultSwitchClauseLast	Enforce default clauses in switch statements to be last	✅
useGetterReturn	Enforce get methods to always return a value.	✅
useIsArray	Use Array.isArray() instead of instanceof Array.	✅ ⚠️
useNamespaceKeyword	Require using the namespace keyword over the module keyword to declare TypeScript namespaces.	✅ 🔧
useValidTypeof	This rule verifies the result of typeof $expr unary expressions is being compared to valid values, either string literals containing valid type names or other typeof expressions	✅ ⚠️

Nursery

Section titled 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
noBarrelFile	Disallow the use of barrel file.
noConsole	Disallow the use of console.	⚠️
noDuplicateJsonKeys	Disallow two keys with the same name inside a JSON object.
noDuplicateTestHooks	A describe block should not contain duplicate hooks.
noEmptyBlockStatements	Disallow empty block statements and static blocks.
noEmptyTypeParameters	Disallow empty type parameters in type aliases and interfaces.
noExcessiveNestedTestSuites	This rule enforces a maximum depth to nested describe() in test files.
noExportsInTest	Disallow using export or module.exports in files containing tests
noFocusedTests	Disallow focused tests.	⚠️
noGlobalAssign	Disallow assignments to native objects and read-only global variables.
noGlobalEval	Disallow the use of global eval().
noInvalidUseBeforeDeclaration	Disallow the use of variables and function parameters before their declaration
noMisleadingCharacterClass	Disallow characters made with multiple code points in character class syntax.	🔧
noNamespaceImport	Disallow the use of namespace imports.
noNodejsModules	Forbid the use of Node.js builtin modules.
noReExportAll	Avoid re-export all.
noRestrictedImports	Disallow specified modules when loaded by import or require.
noSemicolonInJsx	It detects possible “wrong” semicolons inside JSX elements.
noSkippedTests	Disallow disabled tests.	⚠️
noThenProperty	Disallow then property.
noUndeclaredDependencies	Disallow the use of dependencies that aren’t specified in the package.json.
noUnusedImports	Disallow unused imports.	🔧
noUnusedPrivateClassMembers	Disallow unused private class members	⚠️
noUselessLoneBlockStatements	Disallow unnecessary nested block statements.	⚠️
noUselessTernary	Disallow ternary operators when simpler alternatives exist.	⚠️
useAwait	Ensure async functions utilize await.
useConsistentArrayType	Require consistently using either T[] or Array<T>	⚠️
useExportType	Promotes the use of export type for types.	🔧
useFilenamingConvention	Enforce naming conventions for JavaScript and TypeScript filenames.
useForOf	This rule recommends a for-of loop when in a for loop, the index used to extract an item from the iterated array.
useGroupedTypeImport	Enforce the use of import type when an import only has specifiers with type qualifier.	⚠️
useImportRestrictions	Disallows package private imports.
useImportType	Promotes the use of import type for types.	🔧
useJsxKeyInIterable	Disallow missing key props in iterators/collection literals.
useNodeAssertStrict	Promotes the usage of node:assert /strict over node:assert .	🔧
useNodejsImportProtocol	Enforces using the node: protocol for Node.js builtin modules.	⚠️
useNumberNamespace	Use the Number properties instead of global ones.	⚠️
useShorthandFunctionType	Enforce using function types instead of object type with call signatures.	🔧
useSortedClasses	Enforce the sorting of CSS utility classes.	⚠️