RESEARCH · 2026 · ZENODO PREPRINT

Specification Completeness, Not Model Capability, Determines the Reliability of LLM-Generated Backend Code

Six controlled runs, one agent, one task. What varied was the input specification, and that variation decided everything.

6
controlled runs
1
agent and task
2
spec conditions compared

The question

When an AI coding agent produces unreliable backend code, is the model the problem, or the brief it was given? The industry answer is usually to reach for a bigger model. This study tests the other variable.

Method

The same coding agent built the same backend module six times under identical conditions except one: three runs worked from a raw software requirements document, and three worked from a structured build kit, a specification prepared to be complete before any code is written. Every run was scored for reliability and all six outputs are published.

Raw spec · 3 runs Build kit · 3 runs Same agent, same task Score

All six runs are published with their inputs, outputs and scores.

Finding

The completeness of the specification, not the capability of the model, determined whether the generated backend was reliable. The study title is the result.

This finding is also the engineering principle behind CodeNuk, where complete specifications feed a deterministic generation pipeline.