Why AI Coding Assistants Ignore Instructions: Entry File Design

1. The Symptom: It Is Not Just “the Model Not Listening”

When using AI coding tools or coding assistants, developers often run into a familiar frustration: the project instructions clearly say “do not change public interfaces,” “all logging must go through the unified logger,” or “confirm before adding new dependencies,” yet the assistant still bypasses the constraints or follows only some of them. At first glance, it looks like the instructions were ignored. After closer inspection, the problem is often not any single instruction but the context structure in which the instructions sit.

A coding assistant does not work in a vacuum. Within a limited context window, it must understand the project goals, directory boundaries, tech stack, historical conventions, current task, and acceptance criteria at the same time. If all this information is piled into one entry instruction file, that file stops being a navigation card and becomes an encyclopedia. The more information there is, the blurrier the priorities become. The blurrier the priorities are, the more likely the assistant is to latch onto the most recent, most prominent, or most concrete content while missing the truly critical constraints.

A safer way to understand the problem is this: an entry instruction file is suitable only as an entry point. It works like a work card you pick up before entering a repository. It tells the coding assistant what the project is, where the boundaries are, what to look at first, and what counts as done. It should not carry every detail, and it should not replace domain documentation, task specifications, or verification records.

2. The Right Role for an Entry File: A Work Card, Not a Complete Specification

The first responsibility of an entry instruction file is to lower the cost of entry, not to exhaustively list all knowledge. A project may have a complex architecture, historical baggage, coding standards, and release processes, but none of that belongs entirely in the entry file. The entry file should work like a task card at the repository entrance and use a relatively short format to accomplish three things:

1. Establish a project mental model: What does this project do, what does it not do, and what are the core modules?
2. Flag high-risk boundaries: Which parts of the tech stack are easy to guess wrong, which directories must not be changed casually, and which shared capabilities must be reused?
3. Provide completion evidence: Which commands build the project, which checks prove a change is valid, and what result counts as task completion?

If the entry file becomes a several-thousand-line “big and complete” document, it creates three problems: key constraints get drowned out; rules at different levels are mixed together; and the assistant struggles to tell which items are hard constraints and which are background explanation. The more the entry file resembles a work card, the easier it is for a coding assistant to grasp the key points within a limited context.

3. Five Types of Questions the Entry File Should Answer

3.1 What the Project Does and Does Not Do

Project goals should be concise, but boundaries must be explicit. For example: “This repository is responsible for order orchestration, not payment channel integration; payment-related logic may only call the unified interface through the adapter layer.” This kind of description is more useful than simply writing “order service,” because it tells the assistant which changes are in scope and which are out of bounds.

“What it does not do” is especially important. Coding assistants are prone to over-engineering when filling in functionality. If the entry file does not clearly state non-goals, the assistant may introduce a new abstraction layer, replace an existing implementation, or modify modules it should not touch. The entry file should express non-goals as judgeable sentences, not as a vague instruction to “keep it simple.”

3.2 The Tech Stack and Directory Boundaries That Are Easiest to Guess Wrong

Tech-stack descriptions should do more than list frameworks. They should point out where guesses are likely to go wrong. For example: although the project uses a common framework, data access must go through the repository layer; although multiple similar directories exist, only specific directories allow new business code; although utility functions already exist, new logic must reuse the unified wrapper.

Directory boundaries should be written as rules, not maps. For example: “Interface definitions live in api/, domain logic lives in domain/, and infrastructure adapters live in infra/; direct database access from api/ is forbidden.” This kind of description helps the assistant decide where code should go before generating it. A directory list without boundary rules still leaves the assistant free to put logic in the wrong layer.

3.3 Where Common Commands Live

The entry file should provide a discovery path for common commands rather than forcing the assistant to guess. It can list categories such as build, test, static checks, formatting, and local verification, using placeholders to indicate where the project’s actual commands are located. For example:

Build: <build command>
Unit tests: <test command>
Static checks: <check command>
Local verification: <local startup command>

If there are many commands, the entry file should keep only the most common entry points and point to more detailed documentation. This reduces the burden on the entry file and prevents the assistant from inventing commands based on experience.

3.4 What Evidence Counts as Done

“Completing a task” cannot rely only on code looking correct. The entry file should define the minimum acceptance evidence, such as: relevant unit tests pass, static checks pass, critical paths have test coverage, interface changes are reflected in updated documentation, and no new unused dependencies are introduced. The more specific the acceptance criteria are, the less likely the assistant is to declare completion immediately after making changes.

Evidence standards should also distinguish between “must” and “recommended.” Hard requirements should be placed prominently in the entry file, while suggestions can move down into specialized documentation. Otherwise, if all rules are written in the same tone, the assistant will struggle to tell priorities apart.

3.5 Where Problems Have Repeatedly Occurred

Historical issues are one of the most valuable sources of constraints. For example, a certain type of null handling has repeatedly caused production issues, a certain directory has caused build failures due to circular dependencies, or a public interface has affected multiple callers because of a signature change. The entry file does not need to review every incident, but it should abstract recurring problems into check items.

This content should be written as “prevention rules,” not stories. For example: “Changes to public interfaces must list the impact on callers; new asynchronous tasks must explain failure retry and idempotency strategies; amount calculations must use the unified precision tool.” This allows the assistant to apply the rules directly while executing tasks.

4. Why the Entry File Alone Is Not Enough: Layered Context Is Needed

An entry file is suitable only as an entry point because different types of information have different lifecycles. Project goals are relatively stable, task specifications change every time, verification evidence changes with each modification, and historical issues need long-term accumulation. If everything is mixed into one file, maintenance costs rise, and the assistant easily loses focus when reading it.

A more reasonable structure is layered:

• Entry layer: project goals, non-goals, directory boundaries, common command entry points, completion evidence, and high-frequency risks.
• Domain layer: module responsibilities, key flows, interface contracts, and data model descriptions.
• Task layer: current requirements, impact scope, forbidden changes, and acceptance checklist.
• Evidence layer: test results, check records, change notes, and rollback plans.
• History layer: incident reviews, recurring defect patterns, and deprecated approaches.

The entry layer handles navigation and hard constraints, the domain layer explains, the task layer defines the current goal, and the evidence layer supports acceptance. The coding assistant gets direction from the entry layer and reads finer details when needed. This controls context length while preserving traceability.

5. A Reusable Entry File Template

Below is a neutralized structure for an entry file. The point is not the format but the priority of information:

# Project Entry Work Card
## 1. Project Goals
- Does: <one sentence describing the core responsibility>
- Does not do: <explicit non-goals and out-of-scope areas>
## 2. Directories and Boundaries
- Directories where new business logic is allowed: <directory>
- Directories allowed only for adapter calls: <directory>
- Forbidden cross-layer access: <rule>
## 3. Tech Stack Pitfalls
- Framework usage that is easy to guess wrong: <description>
- Shared capabilities that must be reused: <description>
- Rules for adding dependencies: <description>
## 4. Common Command Entry Points
- Build: <command or location of instructions>
- Test: <command or location of instructions>
- Check: <command or location of instructions>
## 5. Completion Evidence
- Checks that must pass: <list>
- Documents that must be updated: <list>
- Impact scope that must be described: <list>
## 6. High-Frequency Risks
- <recurring past issues and prevention rules>

The key to the template is “short and hard.” The entry file should not be too long. Hard constraints should be judgeable, and soft background should move down into other documents. Every rule should ideally answer one question: after seeing it, can the assistant make a different choice? If not, it may be background information and should not occupy an entry-level position.

6. Common Anti-Patterns: Why Entry Files Fail

The first anti-pattern is “rules without priority.” When all content is written in the same tone, the assistant cannot tell which items must be followed and which are merely suggestions. The solution is to distinguish hard constraints, default rules, and background information, and to place hard constraints at the front of the entry file.

The second anti-pattern is “goals without non-goals.” Without non-goals, the assistant easily expands the scope of changes. The solution is to explicitly list the boundaries that this task or this project does not handle.

The third anti-pattern is “directory descriptions that are only lists, not rules.” The assistant knows the directories exist but does not know which layer the logic belongs to. The solution is to rewrite directory descriptions as access rules and placement rules.

The fourth anti-pattern is “vague acceptance criteria.” If the file only says “please make sure tests pass” without specifying test scope, check commands, and evidence format, the assistant has too much room to interpret. The solution is to provide a minimum evidence checklist.

The fifth anti-pattern is “the entry file carrying all documentation responsibilities.” This makes the entry file bloated and hard to maintain. The solution is for the entry file to handle only navigation and hard constraints, while details move down into specialized documentation.

7. Practical Checklist

To help coding assistants follow instructions more reliably, use the following checklist to review the entry file:

• Does it use one sentence to explain what the project does and does not do?
• Does it list the tech-stack usages that are easiest to guess wrong?
• Does it define directory boundaries and rules against cross-layer access?
• Does it provide discovery paths for build, test, and check commands?
• Does it define the minimum evidence for “done”?
• Does it turn recurring past problems into prevention rules?
• Does it distinguish hard constraints, default rules, and background information?
• Does it move long details down into domain documentation or task specifications?

8. Conclusion

When AI coding assistants ignore instructions, it is often not because a single instruction is too weak, but because the entry file is not playing the right role. An entry instruction file is better understood as a work card for entering the repository: it states project goals and non-goals, flags tech-stack and directory boundaries, provides common command entry points, defines completion evidence, and captures high-frequency risks. It is responsible for helping the assistant quickly build a sense of direction, not for replacing all project documentation.

When the entry file is short enough, hard constraints are clear enough, details are layered, and acceptance evidence is executable, coding assistants are more likely to remain stable in complex projects. In other words, the key to reducing ignored instructions is not writing more into the entry file, but putting the right information at the right level and making every key constraint judgeable and verifiable.