A pattern I’ve seen many times in software projects is that documentation starts too late and documents the wrong thing.
A team ships a feature, the code works, the tests pass, and everyone moves on. Maybe someone adds a README section, maybe not. If they do, it usually explains how to run something, how to call an endpoint, or what a component does. That kind of documentation is useful, but it often misses the part future developers need most.
It misses the decision.
Six months later, someone opens the same part of the codebase and asks the usual questions. Why is this data model shaped like this? Why is this rule handled in the backend instead of the frontend? Why is this integration synchronous? Why does this permission check live here? Why did the team choose this simple approach instead of something more flexible?
The code can show what exists, but it rarely explains why it exists. That is where a lot of engineering context disappears.
The Problem Is Not Always Missing Documentation
When people complain about documentation, the usual diagnosis is that there is not enough of it. The README is outdated. The setup instructions are incomplete. The API docs are missing examples. The architecture diagram no longer matches reality.
All of those problems are real. But I think there is another documentation problem that is easier to miss: the docs describe the system without preserving the reasoning behind it.
This matters because software is full of trade-offs. A piece of code may look strange because it was written badly, but it may also look strange because it was solving a constraint that is no longer visible. Maybe the team chose a simpler data model because they were still validating the product. Maybe they avoided a generic abstraction because they had only one real use case. Maybe they accepted duplication because the two workflows looked similar but were expected to diverge.
Without the reasoning, future developers have to guess.
That guessing creates waste. Sometimes they refactor something that should have stayed stable. Sometimes they preserve complexity that no longer has a purpose. Sometimes they repeat the same debate the original team already had, only with less context.
Code Tells You What, Not Why
There is a limit to how much intent code can express. Good naming helps. Clear boundaries help. Tests help. Types help. A well-designed system communicates a lot through structure. But even very good code cannot capture every product constraint, customer conversation, deadline, risk, rejected option, or uncertainty that shaped the decision.
For example, imagine a SaaS product where permissions are implemented with a relatively simple role model: owner, admin, member. A new developer joins later and sees that the model is too simple for some enterprise scenarios. They may assume the original implementation was naive.
But maybe the team considered custom roles and intentionally rejected them. Maybe early users did not need that complexity. Maybe the product was still validating whether teams wanted collaboration features at all. Maybe the decision was not “we do not understand permissions,” but “we are not ready to pay the complexity cost yet.”
That difference matters. The same code can look careless or disciplined depending on the missing context. Documentation should help preserve that context.
The Documentation That Actually Helps Later
The most useful documentation I’ve seen is often short. It does not try to explain every line of code. It explains the decision behind the code.
A good decision note answers a few practical questions:
- What did we choose?
- Why did we choose it now?
- What alternatives did we consider?
- What trade-off did we accept?
- What would make us revisit this later?
That is usually enough.
The goal is not to create a bureaucratic architecture process. The goal is to leave a trail of reasoning for the next person. That next person might be a teammate, a contractor, a future hire, or you three months later when you no longer remember why the obvious solution was rejected.
This is especially important in small teams and early-stage products. In those environments, decisions are often made quickly and informally. A lot of important reasoning lives in chat messages, calls, pull request comments, or someone’s memory. That works while the context is fresh. It breaks down when the product grows.
If a decision affects future work, it deserves a small explanation.
A Simple Example: Choosing Not to Build Flexibility
One of the hardest decisions to document is the decision not to build something.
Teams often document what they add, but they rarely document what they intentionally leave out. This is a problem because future developers may see the missing functionality as an oversight instead of a choice.
Imagine you are building notification preferences. The flexible version might support multiple channels, custom schedules, per-event configuration, team defaults, quiet hours, digest frequency, and user-level overrides. The simple version might support only email notifications for a small set of events.
If you ship the simple version without explanation, someone later may look at it and think: “This is under-designed.” They might be right. But they might also be missing the original product reasoning.
Maybe the team did not yet know which notifications users cared about. Maybe adding full configurability would have slowed down validation. Maybe the most important question was not “can users customize notifications?” but “do users care about these notifications at all?”
That context changes how future work should proceed. A useful note might say:
We are starting with email-only notifications for three core events. We considered per-event preferences and Slack integration, but we do not yet know which notifications users value. We will revisit this after we see usage patterns or receive repeated requests for control.
That is not a long document. But it helps the next developer understand the shape of the decision.
It also prevents accidental overcorrection. Instead of immediately building a complex preference system, the team can ask whether the original signal has changed.
Documentation as Decision Memory
I like thinking about documentation as decision memory.
Not every detail needs to be remembered. Some things are obvious from the code. Some things change too quickly. Some things are better expressed through tests or examples. But decisions that shape future work should not rely entirely on memory.
This is where lightweight architecture decision records can help, but I do not think the exact format matters as much as the habit. A decision can be captured in a pull request description, an issue, a README section, a short decision log, or a project note. The best location is the place your team will actually find later.
The important part is that the decision is close enough to the work to be maintained. A folder full of formal documents nobody reads is not much better than no documentation. A short note in the pull request that explains the trade-off may be more useful than a polished architecture document that goes stale immediately. The format should serve the team, not the other way around.
Why Developers Avoid Writing This Down
There are understandable reasons developers skip this kind of documentation.
Sometimes the decision feels obvious in the moment. Sometimes the team is moving fast. Sometimes writing down the reasoning feels like extra work. Sometimes the decision was messy, uncertain, or political, and nobody wants to make that visible.
But that discomfort is often a signal that the decision is worth documenting.
If the reasoning is obvious, it should be easy to summarize. If it is hard to summarize, the team may not actually agree on the decision. If the trade-off feels uncomfortable, future developers will probably need to know why it was accepted.
I have also noticed that developers sometimes avoid documenting uncertainty because they think documentation should sound confident. I think that is backwards. Good documentation should be honest about uncertainty.
It is useful to write:
We are not sure this model will hold if teams need custom permissions. For now, we are optimizing for the simpler collaboration use case. Revisit this if we see repeated requests for role customization.
That kind of note does not make the team look weak. It makes the decision understandable.
What Not to Document
There is a trap here. Once you start thinking about documentation, it is easy to document too much.
Not every implementation detail needs an explanation. Not every helper function needs a comment. Not every small choice deserves a decision record. Over-documentation creates its own maintenance burden, and stale documentation can be worse than missing documentation because it creates false confidence.
A good filter is to ask whether the decision will matter to someone changing the system later.
If the answer is no, the code and tests are probably enough. If the answer is yes, write down the reasoning. The more expensive the decision is to reverse, the more valuable the explanation becomes.
This is especially true for decisions around:
- data ownership
- permission models
- billing boundaries
- external integrations
- infrastructure constraints
- domain concepts
- product assumptions
- security trade-offs
- major abstractions
- intentionally postponed complexity
These are the areas where future teams lose the most time when context disappears.
A Practical Habit
The habit I would recommend is simple: before merging a meaningful change, add a small decision note.
It can be as short as this:
Decision: We chose X.
Reason: Y matters right now because of Z.
Trade-off: We are accepting A instead of B.
Revisit when: C happens.
That structure is intentionally small. It does not require a new process, a meeting, or a formal architecture board. It can live in the pull request description. If the decision becomes foundational, you can later copy it into a decision log or architecture note.
The point is to capture the reasoning while it is still fresh.
This also improves code review. Instead of reviewers guessing why a design was chosen, they can review the decision directly. They can challenge the assumption, suggest a missing alternative, or agree with the trade-off. The conversation becomes less about personal preference and more about the actual constraint. That is a healthier engineering discussion.
How This Connects to Product Thinking
One reason I care about this topic is that many technical decisions are not purely technical.
A data model reflects product assumptions. A permission system reflects how you think teams will collaborate. A billing boundary reflects what you believe customers will pay for. An onboarding flow reflects what you think users need to understand before seeing value.
If those assumptions are not written down, the codebase starts carrying product decisions that nobody can see clearly.
This is one of the themes behind Hakkle. I am building it around the idea that developers do not only need help typing code. They often need help thinking through planning, architecture, prioritization, and trade-offs while building real software.
Documentation fits into that because good documentation preserves judgment. It helps a project remember why it moved in a certain direction. It helps future work start from understanding instead of archaeology.
That is valuable even when the original decision turns out to be wrong. In fact, it may be most valuable then. If you know why a decision was made, you can tell whether the situation changed. If you do not know why, you may only know that the code feels wrong.
What I’m Taking From This
The lesson I keep coming back to is that documentation does not need to be large to be useful. It needs to preserve the right information.
A setup guide helps someone run the project. API docs help someone use the system. Comments help explain local complexity. But decision notes help future developers understand the path that led to the current design.
Software is not only a collection of files. It is a sequence of decisions made under constraints. Some decisions are technical. Some are product-driven. Some are temporary. Some are compromises. Some are bets. If we do not write down the important ones, the codebase becomes a history with missing chapters.
The next time I make a technical decision that affects future work, I want to leave behind just enough context for the next person to understand it. Not a perfect document. Not a long essay. Just the reasoning that would otherwise disappear.
Future developers do not need to know everything I was thinking. But they should not have to guess the decision from the code alone.
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