Salesforce Debug Logs and Apex Debugging

Debug logs are not captured by default — a trace flag must be set on a specific user (via Setup → Debug Logs) before any of that user's Apex execution gets logged. Forgetting this step is a common first stumbling block: no trace flag means no log appears, even though the code definitely ran.

public static List<AccountResult> search(String searchTerm) {
    System.debug('Searching for: ' + searchTerm);
    List<AccountResult> results = /* ... */;
    System.debug('Result count: ' + results.size());
    return results;
}

System.debug() is the Apex equivalent of console.log — a deliberate statement inserted to inspect a variable's actual value at a specific point during execution, written directly into the resulting debug log.

A debug log has separate verbosity levels per category (Apex Code, Database, Workflow, Validation, and more), ranging from NONE up through FINEST. Setting every category to FINEST captures the maximum possible detail, but also produces an enormous, hard-to-read log — deliberately setting only the relevant categories to a useful verbosity (commonly DEBUG for Apex Code) keeps a log actually readable.

A debug log shows the full execution flow line by line — every SOQL query, every DML statement, every System.debug output — and ends with a summary of governor limit usage (Module 7) for that transaction. This final summary is exactly where a suspected bulkification problem (Module 7's Lesson 6) gets confirmed or ruled out.