Prompts vs. Code: The Cost of No Compiler
03 Sep 2025Thesis: Challenges of writing/maintaining a correct prompt template are far greater than a correct executable code for the same task
A few weeks ago, I opened an agent instruction that had been in production for months. The prompt was nearly a thousand words long, stitched together through dozens of incremental edits. I counted 17 separate instructions marked MANDATORY; scattered unpredictably across the text. The agent still worked, but reading the prompt felt like trying to make sense of a team’s sticky notes shuffled out of order.
That experience reminded me of an uncomfortable truth: prompts accumulate entropy. They bend under the weight of iteration, and unlike code, they lack the structural guardrails that keep complexity in check.
As I work on prompt templates that might be used by hundreds of customers and run thousands of times, I keep hitting the same pain points. These are issues where a small piece of code would be clearer and safer than a sprawling prompt.
Of course, LLMs shine at NLP heavy tasks. But outside those, the differences between “prompt logic” and “code logic” become painfully obvious.
1. Instruction Creep: When Anything Goes
Prompts evolve through many rounds of tweaking. Over time, instructions accumulate in arbitrary places, without any enforced structure. The result is a prompt that works but is difficult to read or reason about.
- Free-form placement: Authors can drop new conditions almost anywhere, often with just a few words of context.
- Ad-hoc fixes: When a data point breaks the prompt, the typical fix is to bolt on another conditional—sometimes flagged with an emphatic MANDATORY. I’ve seen prompts with 17 such “MANDATORY” instructions.
- Inconsistent guidance: Azure’s best practices suggest repeating instructions at the beginning and end of a prompt to offset recency bias. But since this is soft guidance, some authors follow it and others don’t. After multiple contributors iterate, the result is a patchwork of conflicting styles.
With code, the compiler enforces discipline. It forces you into a consistent structure and throws an error if you stray. With prompts, there’s no such safeguard—mess builds silently until readability collapses.
2. Jargon: The Silent Prompt Killer
Unlike code, prompts don’t error out. LLMs will generate something even if they don’t understand your terminology. This makes company jargon invisible landmines.
- Blind token prediction: LLMs are designed to produce the next token whether or not they know the context. They won’t stop and ask for clarification.
- Example: I’ve seen prompts like “If the data is coming from the cascade database, remove the PII.” Here, cascade is an internal database name the model can’t possibly know. The instruction also leaves what counts as PII and how to remove it undefined. The model just guesses.
- Illusion of correctness: Because no error is raised, users assume the system “understood” their intent. In reality, the result is closer to a coin toss.
With code, a missing variable or undefined function throws an error immediately. You’re forced to be explicit—say, by using a PII removal library that requires you to specify the expected patterns. Prompts lack this feedback loop.
3. Refactoring Without a Safety Net
Prompt behavior is brittle, especially compared to code. Small edits can cause outsized and unpredictable shifts in results.
- Sensitivity to details: Word order, synonyms, formatting choices, even an extra space after a colon—all can change outcomes.
- LLM-specific quirks: Studies 1,2, and Azure guidance show these quirks vary across models. What works for one LLM often breaks on another.
- Refactoring risk: Even with strong test coverage, restructuring a prompt is daunting. You may never recover the same eval scores once wording shifts. The messy prompt often “wins” by default.
By contrast, code with good test coverage can be refactored confidently. Tests enforce equivalence. In prompt engineering, no such safety net exists.
Closing Thought
LLMs remove the hard edges of programming: no compiler errors, no enforced structure, no type checks. That flexibility is what makes them powerful—but also what makes prompts messy, fragile, and hard to maintain at scale. When clarity and reliability matter, code is still the safer language.