Intermediate⏱ 5 min read

Error Guessing Technique

Error guessing is an experience-based technique where the tester uses intuition, domain knowledge, and past defect patterns to hypothesise where defects are likely to hide. It complements structured techniques by targeting areas that formal analysis may miss.

◈Key Points

Common error guessing targets: empty inputs, zero values, null, very large numbers, special characters, concurrent users.
Defect taxonomies (organised lists of common bug categories) make error guessing more systematic.
Past defect logs are gold — they show where your specific application has historically been fragile.
Works best when the tester has deep domain and technical knowledge of the system under test.
Pair with exploratory testing for maximum effectiveness.

⚡ Expert Pro Tip

Maintain a personal 'bug notebook' of interesting defects you've found throughout your career. It becomes your own error guessing taxonomy and sharpens your instincts over time.