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A new hire’s first code reviews should do three things: keep unsafe changes out of the codebase, teach the hire how the code and the team actually work, and set clear expectations about what approval means. To get there, prepare the hire before the first pull request, pair them with a reviewer who knows the affected code, give feedback that separates must-fix problems from optional polish, and agree on response times and approval rules in advance. The steps below follow Google’s public engineering guidance, which is the most detailed published account available, and they note where Google’s practice should not be copied as a universal rule.
What a first code review should achieve
Code review has two jobs. The quality job is the familiar one: a reviewer who did not write the change examines it before it lands. Google’s engineering practices documentation describes code review as a process in which someone other than the author examines a piece of code, and it lists design, functionality, complexity, tests, naming, comments, style, and documentation as the dimensions a reviewer weighs.
The learning job matters more for a new hire. Google’s guidance on the standard of code review notes that review can teach developers something new about a language, a framework, or general software design principles. For someone who does not yet know the codebase, the review is often the first place they see why the team does things a certain way. A first review that only ends in a list of fixes wastes that opportunity. A first review that ends with the hire understanding the reasons behind the fixes has done its job.
Concretely, a successful first review leaves three things behind:
#1 Best Overall
- Safe contribution: the change meets the team’s correctness, test, and security expectations before it merges.
- Codebase context: the hire can explain where the change sits in the system and what depends on it.
- Clear expectations: the hire knows who can approve, what a follow-up change needs, and where to take questions that the review thread does not settle.
Prepare the hire before the first pull request
Google Cloud’s documentation on its change process describes intensive onboarding for engineers who are new to Google or its infrastructure. Those engineers study style guides, best practices, and development guides, complete practical exercises, and need extra approval for individual changelist submissions. That is a demanding model built for a very large and specialized environment. Most teams can borrow the underlying idea, which is that a new engineer should not be expected to navigate unfamiliar code and process alone, without copying the approval layer.
A workable preparation pass has five parts:
- Share the review guide. Give the hire the written team standard for reviews, including what reviewers look for and how long reviews are expected to take.
- Share the definition of done. List what a change needs before it can merge, such as tests, documentation updates, feature flags, or migration notes.
- Share style and testing instructions. Link the style guide, the command that runs the test suite locally, and the linter or formatter the CI pipeline enforces.
- Share code ownership information. Tell the hire which owners or maintainers cover each area of the repository, and how ownership is recorded (for example, a CODEOWNERS file, if your platform uses one).
- Walk through the pull request workflow. Do one hands-on session: create a branch, open a pull request, read CI results, respond to a comment, push a follow-up commit, and mark a thread resolved. Do this on a throwaway change so nothing risky is at stake.
Expected result: the hire can open a pull request without asking how to do it, and knows where the rules live. If the hire still needs help with the mechanics after this session, fix the workflow documentation before blaming the hire.
Choose the first change and the first reviewer
Pick a change with bounded scope and manageable risk
The first change should be small enough that a reviewer can explain all of it, and low-risk enough that a mistake does not reach customers. Good candidates include a test addition for an existing module, a documentation fix tied to code the hire has read, a small bug fix with a clear reproduction, or a refactor inside one file. Poor candidates include changes to authentication, billing, data migrations, or shared libraries that many teams depend on, because the review becomes a crisis rather than a lesson.
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Pair the hire with a domain-aware reviewer
Google’s reviewer guidance describes an ideal reviewer as someone capable of giving a thorough and correct review within a reasonable period. For a new hire, the most important attribute is domain knowledge of the affected code, and the second is the willingness to explain. A reviewer who knows the code but is always in a hurry will produce terse comments the hire cannot act on. A reviewer who is friendly but unfamiliar with the module will approve things for the wrong reasons.
Name the reviewer explicitly, and tell them what the job involves: explaining context, pointing to the relevant standards, and deciding what must change before merge. Reviewer count and approval requirements are a separate decision, covered under calibration below.
What the new hire should look for in a review
When the hire reviews other people’s code, or reads comments on their own, they can use the same dimensions Google’s documentation names. This checklist turns those dimensions into questions a new engineer can answer:
- Design: Does the change fit into the existing structure, or does it duplicate a pattern that already exists elsewhere in the code?
- Functionality: Does the code do what the description says, including the edge cases the description mentions?
- Complexity: Could another engineer understand this in a single read? Are there branches or abstractions that exist only for hypothetical future needs?
- Tests: Do the tests fail without the change and pass with it? Do they cover the failure paths, not only the success path?
- Naming: Do variables, functions, and files say what they do in the terms the codebase already uses?
- Comments: Do comments explain why something is done, not restate what the code does?
- Style and documentation: Does the change follow the style guide, and are user-facing or API docs updated where needed?
- Team-specific requirements: Does the change meet any security or reliability rules the team has written down, such as input validation, logging rules, or rollout requirements?
Google’s secure and reliable systems guidance recommends documenting peer review practices and educating new developers about expectations during onboarding to an organization or project. That is the reason to write the team’s security and reliability requirements down in the review guide, rather than leaving them for reviewers to remember.
Give feedback a new engineer can act on
Use a three-part comment pattern
A useful review comment names the issue, explains why it matters, and proposes a concrete next step. Google’s guidance frames the goal of review as continuous improvement rather than perfection, which means a comment should move the code toward the standard without demanding that every line be rewritten. For a new hire, the explanation is the part that carries the learning.
Compare two comments on the same change:
- Weak: “This is wrong. Fix it.”
- Better: “This loop reads the full table on every request, and the endpoint runs once per page view, so the query will slow down as the table grows. Moving the filter into the query, as the other endpoints in this module do, avoids that. Happy to pair on it if the query syntax is unfamiliar.”
Separate required changes from optional suggestions
New engineers often cannot tell whether a comment blocks merge. Label the comments so they can tell. A simple convention is to prefix each comment with a marker such as Required, Suggestion, or Nit, and to define those words in the review guide. Required means the change does not merge until it is addressed. Suggestion means the author should consider it and can reply with a reason to decline. Nit means cosmetic polish that does not block anything.
Keep the number of required items small in a first review. If a change needs twenty required fixes, decide whether the change should be split or redone, rather than sending a long list that the hire cannot prioritize.
Invite questions and explain conventions
Close a comment thread with a question if the author might not know the convention. For example, a reviewer might ask whether the hire has seen the error-handling pattern used in the payments module, then link to an example. Explain conventions once in the review and point to the written guide, rather than correcting the same habit in every file.
Keep review speed and focus time in balance
Google’s speed-of-code-reviews guidance sets one business day as the maximum response time in its own practice. That figure reflects Google’s norm, and teams with smaller reviewer pools or different time zones may need a different target. What transfers is the idea of an explicit target, stated in the team guide, so that a new hire knows whether a silent pull request is normal or stuck.
The same guidance advises reviewers not to interrupt focused work for review requests that can wait. For a new hire, this cuts both ways. The reviewer should acknowledge the request within the agreed window, even if the full review takes longer, and the hire should not treat a quiet afternoon as a rejection. A short acknowledgment such as “I’ll review this by Thursday” covers most of the gap.
Google’s 2022 estimate of wasted engineering time is sometimes cited in this context. Google’s developer blog put the excess cost of interpersonal pushback during code review at more than 1,000 engineer hours per day across the company. That is Google’s own internal estimate, not an industry-wide measure, and it does not show how much time any other team loses to review friction.
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Close the loop on approval and follow-up
A review ends in one of three states: approved, approved with follow-up, or not yet approved. A new hire needs to know which applies and what they must do next. Write these answers into the review guide:
Best Value
- What approval means: the reviewer judges the change acceptable for the requested scope, and the author remains responsible for the code after merge.
- Who can approve: the reviewer roles that count toward merge, and whether a new hire’s change needs an additional approver.
- How follow-up changes are reviewed: whether the original reviewer checks new commits, or whether a fresh review is required after substantial changes.
- Where unresolved questions go: a named channel, a mentor, or a design discussion thread, so questions do not stay buried in a closed pull request.
Google Cloud’s account of its change process describes extra approval for individual changelist submissions during onboarding. That is a specific Google policy. Whether a new hire’s changes need a second approver is a decision for each team to make and write down.
Calibrate for experience and risk
The right amount of support and scrutiny depends on the hire’s familiarity and the change’s risk. Five factors matter most, and the table shows how they change the setup for a first review:
| Factor | Lower support or scrutiny | Higher support or scrutiny |
|---|---|---|
| Codebase and tooling familiarity | Hire has completed the workflow walkthrough and has shipped before in this repository | Hire is new to the repository and the build or test tooling |
| Risk and scope of the change | Test-only or documentation change inside one module | Change touches authentication, data migrations, or shared libraries |
| Reviewer expertise in the affected area | Reviewer owns the module and has reviewed similar changes | Reviewer is a generalist, so a second reviewer with domain knowledge is added |
| Team approval and ownership rules | Standard approval rules apply, with the hire as author | Team policy requires an additional approver for the hire’s first changes |
| Explanation needed to act on feedback | Hire acts on comments without follow-up discussion | Hire needs a pairing session or written example for each comment type |
Reviewer counts and approval requirements are not established as universal values by the sources Google publishes. Set them against your own risk profile, not against another company’s process.
Common failure modes and fixes
- The hire waits silently for days. Check whether the reviewer was named and told the expected response time. If not, reassign the review and state the target in the guide.
- Comments are correct but the hire cannot act on them. Add an explanation of the reason to each required comment, and offer a pairing session for the next change.
- The hire stops asking questions. Reviewers should ask a question in the thread, not wait for the author to raise one. Review the channel where unresolved questions go and confirm the hire knows it exists.
- Every comment is marked required. Re-label the comments using the required, suggestion, and nit convention, and split the change if the required list is still long.
Where Google’s practice applies and where it does not
Google’s engineering practices are the most detailed public account of code review, and they describe the goal of review, the reviewer’s job, and the speed expectations clearly. Google Cloud’s onboarding model and Google Research’s historical case study on practice-based learning show how a very large organization builds a learning path for new engineers. Treat the Google Research material as a case study of one organization’s history rather than a benchmark that predicts what your team will see. The same applies to every specific number Google publishes, including its one-business-day response norm and its 2022 hours estimate.
What transfers directly is the structure: prepare the hire, match the reviewer to the code, separate required from optional feedback, state the response target, and define approval before the first review begins.
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