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Overview Get real-time diagnostics (errors, warnings, and informational messages) for your Python code. This provides the same error detection you see in your IDE’s Problems panel.
Request File URI (e.g., file:///workspace/main.py)
Filter by severity: error, warning, information, hint
Response Array of diagnostic messages Location of the issue Start position (line, character)
End position (line, character)
Severity level: 1 (Error), 2 (Warning), 3 (Information), 4 (Hint)
Error code (e.g., undefined-variable, type-mismatch)
Human-readable description of the issue
Always Pylance for this server
Example Request cURL
Python
JavaScript
TypeScript
curl -X POST https://api.pylancemcp.dev/v1/tools/call \ -H "Authorization: Bearer YOUR_API_KEY" \ -H "Content-Type: application/json" \ -d '{ "name": "get_diagnostics", "arguments": { "uri": "file:///workspace/app/views.py" } }'
Example Response { "diagnostics" : [ { "range" : { "start" : { "line" : 15 , "character" : 8 }, "end" : { "line" : 15 , "character" : 21 } }, "severity" : 1 , "code" : "undefined-variable" , "message" : " \" undefined_var \" is not defined" , "source" : "Pylance" }, { "range" : { "start" : { "line" : 23 , "character" : 12 }, "end" : { "line" : 23 , "character" : 26 } }, "severity" : 2 , "code" : "type-mismatch" , "message" : "Argument of type \" str \" cannot be assigned to parameter \" amount \" of type \" int \" in function \" calculate \" " , "source" : "Pylance" }, { "range" : { "start" : { "line" : 42 , "character" : 0 }, "end" : { "line" : 42 , "character" : 6 } }, "severity" : 3 , "code" : "unused-import" , "message" : "Import \" typing \" is not accessed" , "source" : "Pylance" } ], "errorCount" : 1 , "warningCount" : 1 }
Diagnostic Types Errors (Severity 1) Code Description Example undefined-variableVariable not defined print(unknown_var)type-mismatchType doesn’t match expected calculate("5") when expecting intimport-not-foundModule cannot be imported import nonexistent_modulesyntax-errorInvalid Python syntax def foo( (missing closing paren)missing-argumentRequired parameter not provided calculate() when calculate(x) expected
Warnings (Severity 2) Code Description Example unused-importImport never used import os but os not referencedunused-variableVariable assigned but never used temp = 5 but temp not usedduplicate-importModule imported multiple times import json twiceunreachable-codeCode that will never execute Code after return deprecatedUsing deprecated functionality collections.Mapping instead of collections.abc.Mapping
Code Description Example missing-type-hintType annotation missing def foo(x): instead of def foo(x: int):convention-violationStyle guideline not followed Function name not snake_case
Use Cases Pre-Commit Validation # Check for errors before committing files_to_check = get_changed_files() for file in files_to_check: diagnostics = client.get_diagnostics( uri = file ) if diagnostics.error_count > 0 : print ( f "❌ Cannot commit: { file } has errors" ) for diag in diagnostics.diagnostics: if diag.severity == 1 : print ( f " Line { diag.range.start.line + 1 } : { diag.message } " ) exit ( 1 ) print ( "✅ All files are error-free" )
Continuous Monitoring # Watch for new errors as code changes def monitor_file ( file_uri ): previous_errors = set () while True : diagnostics = client.get_diagnostics( uri = file_uri) current_errors = { (d.range.start.line, d.message) for d in diagnostics.diagnostics if d.severity == 1 } # New errors appeared new_errors = current_errors - previous_errors if new_errors: for line, message in new_errors: print ( f "🚨 New error at line { line + 1 } : { message } " ) previous_errors = current_errors time.sleep( 2 )
Code Quality Metrics # Calculate code quality score def calculate_quality_score ( workspace_files ): total_errors = 0 total_warnings = 0 for file in workspace_files: diagnostics = client.get_diagnostics( uri = file ) total_errors += diagnostics.error_count total_warnings += diagnostics.warning_count # Score: 100 - (10 * errors) - (2 * warnings) score = max ( 0 , 100 - ( 10 * total_errors) - ( 2 * total_warnings)) return { "score" : score, "errors" : total_errors, "warnings" : total_warnings, "grade" : "A" if score >= 90 else "B" if score >= 80 else "C" }
Filtering by Severity Get only specific severity levels:
Errors Only
Warnings and Above
diagnostics = client.get_diagnostics( uri = "file:///workspace/app/views.py" , severity = "error" ) # Only severity 1 (errors) returned
Incremental Updates : Only check files that changed, not entire workspace
Debounce Checks : Wait 500ms-1s after typing stops before checking
Cache Results : Diagnostics don’t change unless file changes
Error Responses Code Reason Solution FILE_NOT_FOUNDFile doesn’t exist Verify file path INVALID_PYTHONFile is not Python Check file extension and content PARSE_ERRORCannot parse file File has syntax errors preventing analysis WORKSPACE_NOT_LOADEDWorkspace still loading Wait for initialization
Rate Limits Tier Requests/Hour Requests/Day Free 20 100 Hobby 500 5,000 Pro 5,000 50,000 Enterprise Unlimited Unlimited
Get Code Actions Get quick fixes for diagnostics
Format Document Auto-format code to fix style issues
Get Hover Get more info about errors
Apply Workspace Edit Apply fixes automatically
