q Linter

QStudio includes a built-in linter for kdb+/q code that checks for errors, warnings and code quality issues. The linter runs automatically when you save a file and reports issues in the Problems Panel.

The linter catches common mistakes including:

• Assigning to reserved words like count or sum
• Unused variables and parameters
• Undeclared variables that will become unintended globals
• Deprecated internal functions that have q replacements
• Wrong number of arguments to namespace functions
• Code after a return statement (unreachable code)

Problems Panel

Lint results appear in the Problems Panel at the bottom of the screen. Each row shows the severity, file, line number, rule ID and message. Click any row to jump directly to the problem in the editor.

The Problems Panel updates automatically when you save a file. Only .q and .k files are linted.

Editor Highlighting

When filtering is enabled, lint issues are highlighted directly in the editor with:

• Squiggly underlines beneath the affected code — red for errors, orange for warnings, blue for info
• Colored circles in the gutter next to line numbers

Highlights clear automatically if you add or remove lines (since positions may shift) and reappear when you save.

The highlighting colors adjust for dark and light editor themes.

Filtering by Severity

The filter button in the Problems Panel toolbar cycles through severity levels:

Filter	Shows
ALL	Errors + Warnings + Info
ERROR	Errors only
WARNING	Warnings + Errors
INFO	Info + Warnings + Errors (everything)
NONE	Nothing — hides all lint results and editor highlights

The default is NONE so existing users are not surprised by new highlighting. Click the filter button to enable error display.

Changing the filter also updates the editor highlighting in real-time.

Configuring Rules

Click the gear icon in the Problems Panel toolbar to open the Configure Lint Rules dialog. Each rule can be individually enabled or disabled. Use the Select All / Select None buttons for quick toggling.

Rule configuration is per-session. Disabled rules are not persisted between restarts.

Suppressing Rules Per File

Add a comment at the top of your q file to suppress a specific rule for that file:

/ @qlintsuppress UNUSED_VAR

This prevents the UNUSED_VAR rule from firing anywhere in that file. Multiple rules can be suppressed with separate comments.

Cross-File Analysis

When you have a folder open, the linter performs cross-file analysis. It builds an index of all namespace functions defined across your project files and can detect:

• Undefined references — calling .trade.getPrice when no file defines it (and the .trade namespace is known)
• Wrong argument count — calling a function with more arguments than it accepts
• Parameter type mismatches — passing a string literal where a parameter named sym expects a symbol

Built-in namespaces (.Q, .q, .z, .h, .j, .o, .m, .log) are never flagged since their contents cannot be verified statically.

All Lint Rules

The linter includes 38 rules across four categories.

Error Detection

Rule	Severity	Description
ASSIGN_RESERVED_WORD	ERROR	Assignment to a reserved word (e.g. count:42)
COND_EVENARGS	ERROR	Conditional $ has even number of arguments (should be odd)
INVALID_ESCAPE	ERROR	Invalid escape sequence in string (e.g. "\q")
INVALID_ASSIGN	ERROR	Attempt to assign to a string, symbol, or number
DECLARED_AFTER_USE	ERROR	Variable was used before being declared
TOO_MANY_LOCALS	ERROR	Too many local variables in function (max 110)
TOO_MANY_GLOBALS	ERROR	Too many global assignments in function (max 20)
TOO_MANY_CONSTANTS	ERROR	Too many constants in function (max 110)
GLOBAL_PEACH	ERROR	Modifying globals inside peach is not allowed
RESERVED_NAME	ERROR	File has a name that conflicts with a q reserved word
UNDEFINED_REFERENCE	ERROR	Reference to undefined symbol in a known namespace (cross-file)
WRONG_ARG_COUNT	ERROR	Function called with wrong number of arguments (cross-file)
PARAM_TYPE_MISMATCH	ERROR	Literal argument type conflicts with parameter name hint (cross-file)
DEPRECATED_INTERNAL	ERROR	Internal function -N! has a q replacement (e.g. use parse instead of -5!)
UNARY_FORM	ERROR	Unary operator form (e.g. #:) should use q keyword (e.g. count)

Code Quality Warnings

Rule	Severity	Description
DEPRECATED_DATETIME	WARNING	Datetime type has been deprecated in favour of timestamp
EMPTY_IF	WARNING	If statement lacks code to execute
CAST_TYPE_NUMERICAL	WARNING	Casting using short type indicator (e.g. "i"$) is unnecessarily unclear
UNUSED_PARAM	WARNING	Parameter declared but never used in the function body
UNUSED_VAR	WARNING	Variable assigned but never referenced
UNDECLARED_VAR	WARNING	Undeclared variable will be treated as global
UNREACHABLE_CODE	WARNING	Code after a return statement is never executed
NEED_EXPLICIT_RETURN	WARNING	Function ends with assignment — returns generic null instead of a value
DEBUG_FUNCTION	WARNING	Debug function call (e.g. show) should not be in release code
CONDITIONALLY_DECLARED	WARNING	Variable may be undefined — declared only in one branch of a conditional
NAME_COLLISION	WARNING	Assignment could overwrite a built-in function
BACKWARD_COMPATIBILITY	WARNING	Feature may not be available in older kdb versions

Style Warnings

Rule	Severity	Description
LINE_TOO_LONG	WARNING	Line exceeds maximum length (default 120 characters)
FUNCTION_TOO_LONG	WARNING	Function exceeds maximum line count (default 40 lines)
TOO_MANY_PARAMS	WARNING	Function has too many parameters (default max 8)
UNDERSCORE_IN_NAME	WARNING	Underscore in name conflicts with the drop operator _
XYZ_AS_LOCAL	WARNING	x/y/z used as local variable — reserved for implicit parameters
TRAILING_SEMICOLON	WARNING	Trailing semicolon before } causes function to return generic null
UNINDENTED_CODE	WARNING	Multiline expression must be indented after first line

Informational

Rule	Severity	Description
IMPLICIT_PARAMS	INFO	Function uses implicit parameters (x/y/z) — consider naming them
MULTIPLE_STATEMENTS_PER_LINE	INFO	Multiple statements on one line
TODO_MARKER	INFO	TODO, FIXME, HACK or XXX marker found in comment