What Does a Principal Engineer Do?
Module 4 of 4 Intermediate 25 min

A Week in the Life — What a Principal Engineer Actually Does

Prerequisites: How Engineers Level Up — The Career Ladder and Its History, Two Paths Forward — How Tech Companies Let Great Engineers Stay Engineers, One Title, Three Flavours — The Types of Principal Engineers

What You'll Learn

  • Describe at least three concrete activities that fill a Principal Engineer's typical week — including writing strategy documents, reviewing technical proposals, parachute problem-solving, and mentoring.
  • Explain why a Principal Engineer writes less code than a junior engineer, and why this is the opposite of what most people expect.
  • Describe how a Principal Engineer's decisions can shape the work of dozens or hundreds of engineers without ever giving a direct order.

Why This Matters

The previous modules gave you the structure: the career ladder, the dual-track system, the three archetypes. But structure alone doesn't answer the dinner-table question. What does a Principal Engineer actually do between Monday morning and Friday afternoon?

This matters because the answer is surprising. Most people assume that the most senior technical person must be doing the most intense, all-day coding. The reality is close to the opposite — and understanding why that is will help you explain one of the most misunderstood roles in the tech industry. By the end of this module, you'll have a specific, concrete picture of a real week, and a two-or-three sentence summary you could say out loud tonight.

Core Concept

The Code Paradox

Here is the thing that surprises almost everyone: a Principal Engineer writes less code than a junior engineer. A junior engineer might spend five or six hours a day writing code. A Principal Engineer might spend one or two. And yet the Principal Engineer earns more, holds more responsibility, and has a greater effect on what gets built.

This seems backwards. Shouldn't the most senior person be the best coder? Shouldn't they be coding the most?

The answer requires a shift in how you think about what "work" means in a technical organization. A junior engineer's job is to build a specific thing well. A Principal Engineer's job is to make sure the entire organization is building the right things in the right ways — and that is not a job you can do with code alone.

Think of it this way: if a junior engineer solves a problem, that problem is solved. If a Principal Engineer helps ten engineers understand how to think about a class of problems, ten problems get solved better, year after year. The leverage comes from breadth, not depth. They still write some code — typically 20 to 30 percent of their week — because staying close to real implementation keeps their strategic thinking grounded in reality. A Principal Engineer who stops writing code entirely risks becoming a strategist disconnected from the actual problems engineers face.

The Shape of a Typical Week

A Principal Engineer's week contains four recognizable kinds of work, and each one illustrates a different facet of the role.

Reviewing technical proposals. When a team of junior or mid-level engineers designs a new feature or system, they often write a document explaining their approach and ask for feedback from senior engineers. A Principal Engineer reads these proposals and responds — not by rewriting them, but by asking probing questions and identifying risks the team may not have seen. "Have you considered what happens when the load triples?" or "There's a team on the data side that solved almost the same problem last year — have you talked to them?" The team then revises their approach and executes independently. The Principal Engineer never touched a single line of their code, but their intervention prevented a costly mistake and connected two teams who didn't know they needed each other.

Writing strategy documents. This is perhaps the least visible work from the outside, and the most impactful. A Principal Engineer might spend two full days — sometimes longer — writing a ten- to fifteen-page document that addresses a major technical question facing the company: should we move to a different database system (the software that stores all the company's records)? How should we handle our security model over the next three years? The document surveys the options, weighs the trade-offs, recommends a path, and explains the reasoning. It then gets shared across the organization, and for the next year or two, fifty engineers make day-to-day decisions guided by it. The Principal Engineer never told any of them what to do. But their thinking shaped every one of those decisions.

Parachute problem-solving. Critical problems sometimes arise that no single team can solve alone, because the problem cuts across multiple systems that no single team owns. A production outage (when a product stops working for users) might involve the web layer, the payment system, and the data storage system all interacting in unexpected ways. A Principal Engineer is called in precisely because they have the organizational reach — that is, how many teams, products, or people are affected by an engineer's decisions — to see across those boundaries and propose a solution. They are, in the language of software engineering, "the person who knows where all the skeletons are."

Mentoring. A Principal Engineer who spends an hour a week with a mid-level engineer — working through a difficult technical decision, recommending the right paper to read, or simply explaining how the organization makes architectural choices — is investing in that engineer's growth. Over months and years, that investment compounds. A better engineer makes better decisions, documents better, reviews better. Mentoring is how a Principal Engineer multiplies their impact beyond anything they could accomplish alone.

Organizational Reach Without Authority

All four of these activities share a crucial feature: none of them involve giving orders. A Principal Engineer is a senior individual contributor — that is, an engineer who advances through technical expertise and does not manage other people. They cannot tell anyone to follow their strategy document. They cannot order a team to revise their proposal. They cannot require a junior engineer to meet with them.

Everything they accomplish happens through leading through credibility — the mechanism by which individual contributors shape decisions and direction through demonstrated expertise and earned trust, not through formal authority or the power to hire or fire. People follow a Principal Engineer's recommendations because those recommendations have proven right before, because the reasoning is clear and compelling, and because the Principal Engineer has spent years building a reputation for sound judgment.

This is what distinguishes a Principal Engineer from a manager. A manager has formal authority over a team: they can direct the team's work, make personnel decisions, and hold people accountable through the organizational hierarchy. A Principal Engineer has zero formal authority and no one reporting to them — but potentially a larger organizational reach: how many teams, products, or people are affected by their decisions.

Concrete Example

Let's walk through Sarah's week. Sarah is a Principal Engineer at a tech company of five hundred to a thousand people. Her younger sibling asked at dinner last week: "What exactly do you do?" This is the week Sarah would describe.

Monday. A junior team has written a proposal for a new recommendation system (the feature that suggests products or content to users). They've asked for feedback before they start building. Sarah reads the twelve-page document over coffee, then spends ninety minutes writing a detailed response. She points out that they've designed their system to store all the recommendation history forever — which will be expensive — when 90 percent of the value comes from the last thirty days. She also connects them with a team on the other side of the company that built something similar eight months ago. The junior team wasn't aware that team existed. Sarah never touches their code. By the end of the week, the junior team has a substantially better plan.

Tuesday and Wednesday. Sarah spends nearly two full days on a strategy document about which database technology the company should adopt for its next generation of products. She interviews four engineers from different teams, reviews three external research reports, and drafts a fifteen-page recommendation with a detailed analysis of trade-offs. By the end of Wednesday she has a document that, once approved, will guide the technical choices of about sixty engineers for the next eighteen months.

Thursday. At 10 a.m., a critical system fails. Payments are not processing for a portion of users. Three teams are working on it but cannot identify the root cause because it involves an interaction between the payment service, the identity verification system, and a third-party integration — three systems owned by three different teams, none of whom has full visibility into the others. Sarah joins the incident call, asks a series of questions across each system, and within forty minutes identifies the cause: a recent change in the identity system is producing a data format the payment service doesn't recognize. She proposes a temporary fix that two teams can implement in parallel. By noon, payments are restored. That afternoon, she writes up a post-mortem (a document that explains what happened and how to prevent it) so the same failure mode can't recur.

Friday. Sarah meets with a mid-level engineer named Dev who is preparing to propose a significant architectural change to one of the company's core systems. She doesn't tell Dev what to propose — she asks him questions: "What does success look like in a year? What would make you regret this decision?" By the end of the hour, Dev has a clearer sense of what he actually wants to recommend, and why. Sarah suggests two papers he should read before he writes the proposal.

At the family dinner, Sarah describes this week to her sibling, who listens and then says: "So you're like a consultant who actually works there."

Sarah smiles. "Sort of. Except I've been here long enough to know where all the skeletons are, and people trust me because I've been right before."

Analogy

Imagine the person who designed the master plan for your city. Not the person who poured the concrete or framed the houses — the urban planner who decided where the roads would go, how the neighborhoods would be zoned, where the parks would be placed, and what the building height limits would be in the city center.

Every builder who constructs a house or office in that city works within the urban planner's framework. They follow the zoning rules, build to the setback requirements, connect to the streets the planner laid out. The urban planner never told any individual builder what to do on any given Tuesday. But their decisions shaped everything those builders built.

A Principal Engineer is the urban planner of their organization's technical landscape. They write the "zoning rules" — the technical standards and architectural patterns. They design the "infrastructure" — the shared systems and platforms other teams build on. And when a neighborhood (a team) wants to do something that conflicts with the city's long-term plan, the urban planner is the one who explains why, proposes a better path, and helps them see the bigger picture.

The analogy also captures the paradox of code: an urban planner doesn't lay bricks. Not because they don't know how — they deeply understand construction — but because their contribution is at a different level of abstraction. The same is true of a Principal Engineer.

There is a second way to picture the same dynamic. Think of the head chef of a restaurant group that runs a dozen locations. They do not cook every meal at every restaurant. But they developed the core recipes, set the kitchen standards, trained the other head chefs, and they still cook on the line regularly enough to know when a supplier's ingredients have changed. Remove them from the kitchen entirely and the standards drift. The Principal Engineer's twenty to thirty percent of hands-on coding plays the same role: it keeps the strategy honest.

Going Deeper

The Leverage Question

One way to understand the Principal Engineer role is to ask: "What is the highest-leverage use of this person's time?" For a junior engineer, the answer is usually: write good code. For a Principal Engineer, the answer is almost always something that multiplies other engineers' effectiveness — a strategy document that guides fifty engineers, a mentoring conversation that unlocks a mid-level engineer's next two years of growth, a cross-team connection that prevents six months of duplicated work.

This is why Principal Engineers at most large tech companies are not measured by the number of features they ship or the amount of code they write. They are measured by outcomes that are harder to count: did the organization make better technical decisions? Did engineers grow faster? Did the company avoid costly architectural dead ends?

The Writing Requirement

One underappreciated aspect of the role is how much writing it requires. Strategy documents, design reviews, post-mortems, technical standards, mentoring feedback — a Principal Engineer's primary output is often written words, not running code. This surprises people who think of engineering as a fundamentally hands-on discipline. But in a distributed organization, written documents are how decisions survive handoffs, scale across time zones, and outlast the people who made them. A Principal Engineer who can't write clearly is severely limited in their effectiveness.

The Loneliness of No Direct Authority

Leading through credibility is powerful, but it comes with a cost. A manager who gives a direction and isn't followed can escalate — they have formal authority to enforce compliance. A Principal Engineer who writes a strategy document that teams choose to ignore has no equivalent recourse. They must go back, understand why the document wasn't persuasive, revise their thinking, have more conversations, build more trust. Some Principal Engineers find this deeply motivating — the challenge of earning influence rather than wielding power. Others find it exhausting. It is, at minimum, a different kind of challenge than most people expect from a "senior" role.

Common Misconceptions

Misconception 1: "They code less because they're too senior for it — it's beneath them."

This gets the reason exactly wrong. A Principal Engineer writes less code not because coding is beneath them, but because their leverage is higher elsewhere. The best Principal Engineers stay close to code — typically 20 to 30 percent of their time — precisely because they know that losing touch with real implementation makes their strategies impractical. They write less code because their time is worth more as a force multiplier on other engineers' work. Coding remains something they respect deeply and return to regularly.

Misconception 2: "They're basically managers without the title."

The authority structures are opposite. A manager has formal power over a team: they direct work, conduct performance reviews, make hiring decisions, and are accountable for the team's output. A Principal Engineer has no one reporting to them and no formal power over anyone. Their entire effectiveness rests on leading through credibility — demonstrated expertise and earned trust. Some find a Principal Engineer's reach actually exceeds a typical manager's, precisely because it isn't bounded by an org chart. But the mechanism of that reach is entirely different.

Misconception 3: "They must have all the answers — that's why people listen to them."

Principal Engineers operate in genuine uncertainty. Many of the questions they work on have no objectively right answer — only trade-offs, incomplete information, and competing priorities. What makes them valuable isn't certainty; it's the ability to surface the right questions, gather evidence systematically, reason through trade-offs clearly, and then make a call and explain it in a way that helps others understand and commit. Their authority comes from the quality of their reasoning process, not from having arrived at pre-existing answers.

Check Your Understanding

  1. Sarah spends Tuesday and Wednesday writing a strategy document instead of building a feature. Her sibling thinks this doesn't look like "real work." How would you explain why this is actually the highest-leverage activity Sarah could be doing those two days?

    Reveal answer The strategy document will guide approximately sixty engineers' decisions for the next eighteen months. If Sarah instead spent those two days writing code, she might complete a small feature that one team uses. The document's reach is orders of magnitude larger — it shapes the work of far more people for far longer. This is why written strategy is often a Principal Engineer's most important output, even though it looks less "productive" to an outside observer.

  2. When a critical outage occurs on Thursday, why is Sarah specifically the right person to call — rather than, say, a senior engineer from the payment team or the identity verification team?

    Reveal answer The outage was caused by an interaction *between* three systems owned by three different teams. Each individual team could only see their own piece. Sarah's value comes from her **organizational reach** — her familiarity with how multiple systems across the company interact. No single team had the cross-system view needed to identify the root cause. This "parachute" capacity to see across boundaries is a defining feature of the Principal Engineer role.

  3. A manager and a Principal Engineer both want to change how a team writes software. The manager sends a directive. The Principal Engineer sends a well-reasoned document and holds a meeting. What happens if the team resists each approach, and what does that reveal about the difference between the two roles?

    Reveal answer If the team resists the manager's directive, the manager can escalate through the formal hierarchy — their authority is backed by organizational power. If the team resists the Principal Engineer's recommendation, the Principal Engineer has no equivalent recourse. They must understand the team's objections, revise their reasoning, rebuild consensus, and try again. This reveals the core distinction: a manager leads through formal authority; a Principal Engineer leads through **leading through credibility** alone. Neither is inherently superior, but they are fundamentally different mechanisms.

  4. Why does it matter that Sarah still writes code for 20 to 30 percent of her week, rather than spending all her time on strategy and mentoring?

    Reveal answer Staying close to real implementation keeps a Principal Engineer's strategic thinking grounded. If Sarah stopped writing code entirely, her strategy documents would increasingly reflect how she *imagines* engineering works rather than how it actually works in practice today. The code she writes — even a small fraction of her week — gives her continuous feedback that makes her strategic work more accurate and credible. It also maintains her standing with other engineers, who trust her in part because she is still "in the trenches" alongside them.

  5. Sarah's sibling says: "So you're like a consultant who actually works there." What does this capture well about the Principal Engineer role, and what does it miss?

    Reveal answer It captures the advisory, cross-cutting nature of the role well — a consultant analyzes problems, recommends solutions, and moves between different parts of an organization rather than staying within one team. What it misses is the depth of institutional knowledge and trust that makes a Principal Engineer's recommendations credible. A consultant is brought in from outside; a Principal Engineer has earned their authority over years of being demonstrably right, which is why people follow their recommendations. Sarah refines the analogy precisely: "I've been here long enough to know where all the skeletons are."

Key Takeaways

  • A Principal Engineer writes less code than a junior engineer not because coding is beneath them, but because their leverage is highest as a force multiplier on other engineers' work — through strategy documents, proposal reviews, mentoring, and cross-system problem-solving.
  • Their primary output is often written: strategy documents, design reviews, and technical standards that shape dozens or hundreds of engineers' decisions without any direct orders.
  • The "parachute" capacity — the ability to drop into a critical situation that has stumped others and see across system boundaries — is one of the most distinctive and valued capabilities of the role.
  • Everything a Principal Engineer accomplishes rests on leading through credibility: demonstrated expertise and earned trust, not formal authority. They have no one reporting to them and no power to enforce compliance.
  • Dinner-table answer: A Principal Engineer is a very senior technical expert who shapes how the whole company builds software — setting standards, solving the hardest problems, and guiding other engineers — without managing anyone directly. They've earned enough trust that their recommendations carry real weight, even though they have no official power over the people who follow them.

References