Semantic Debt
The gradual, invisible divergence between what your code does and what your team thinks it does.
Assumption
"This flag enables the new payment flow"
"User IDs are always UUIDs"
"The cache expires after 5 minutes"
"Power Peg was removed in 2008"
Reality
"On 7 servers, yes. On 1 server, it activates Power Peg"
"Except in the legacy API, where they're integers"
"In prod: 5min. In staging: 30min. In dev: never"
"Disabled, not removed. Still in the codebase"
Definition
Semantic debt occurs when the documented behavior, intended logic, or understood purpose of a system diverges from its actual runtime behavior.
Unlike technical debt, which you can see and measure, semantic debt is invisible. Your tests pass. Your code compiles. Your monitoring is green. But your system no longer means what you think it means.
It accumulates through feature flags that outlive features, configurations that vary across environments, dead code that isn't dead, tribal knowledge that leaves with employees, and undocumented dependencies between modules.
Semantic Debt vs Technical Debt
| Technical Debt | Semantic Debt | |
|---|---|---|
| Visibility | Visible in code | Invisible until triggered |
| Detection | Linters, code smell tools | Semantic analysis required |
| Impact | Slows development | Causes catastrophic failures |
| Example | Copy-pasted code, missing tests | Repurposed flags, config divergence |
| When it appears | During development | In production, under load |
Why Existing Tools Fail
Static Analysis
Finds syntax errors and code smells, but can't detect semantic gaps.
Power Peg code was syntactically correct. It just shouldn't have existed.
Unit Tests
Verify code does what tests expect, not what documentation claims.
If nobody knows code exists, nobody writes tests for it.
Code Review
Catches problems in changes, not in what's already there.
Knight's deployment was reviewed. But Power Peg wasn't in the diff.
Monitoring
Watches for known failure modes, not unknown semantic gaps.
"Accidentally reactivated 7-year-old algorithm" wasn't on the dashboard.
The AI Era Accelerates This
AI coding assistants generate code 10x faster than humans can verify it. Semantic debt that used to accumulate over years now accumulates over months.
How APX Solves This
APX makes semantic debt visible, verifiable, and governable through Feature Packs with embedded constraints and continuous semantic verification.
Semantic Boundaries
Every module, feature, and flag mapped to its business purpose
Constraint Verification
Formal rules encoded and checked automatically
Lineage Tracking
Know exactly what runs where and why
Further Reading
Software That Evolves Itself
A comprehensive exploration of self-evolving software systems and the challenges they present for modern engineering teams.
Read on LinkedIn