A new hire’s first code reviews should do three jobs at once: keep the change safe, teach the hire how your codebase and team work, and make clear what “approved” means. You get there by preparing the hire before the first pull request, choosing a change with bounded risk, pairing them with a reviewer who knows the affected code, and giving feedback that separates required fixes from optional polish.
What a first code review should accomplish
Google’s engineering practices guide describes code review as “a process where someone other than the author(s) of a piece of code examines that code.” That definition covers the quality function of review, but a first review also has a learning function. The same guide notes that review “can have an important function of teaching developers something new about a language, a framework, or general software design principles” (Google Engineering Practices Documentation, “The Standard of Code Review”).
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For a new hire, that points to three goals to hold in mind for every first review:
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- Safe contribution: the change does what it claims, is tested, and does not break something the hire cannot yet see.
- Codebase context: the hire learns where things live, why they are built that way, and which conventions the team relies on.
- Clear expectations: the hire knows what review feedback is required, what is a suggestion, who can approve, and how follow-up work is handled.
If a review only checks whether the code is acceptable and never explains why, the hire learns the outcome but not the reasoning, and the next change will need the same correction.
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Prepare the hire before the first review
Google Cloud’s documentation describes onboarding for engineers new to its infrastructure as extensive. New engineers there study style guides, best practices, and development guides, and complete practical exercises before working independently. That approach suits a large, specialized environment. A smaller team can reach the same outcome with a lighter set of materials. Before the hire opens a first pull request, give them:
- The team’s review guide, covering what reviewers look for, how long a review usually takes, and how to request one.
- The definition of done, so the hire knows what must be true before a change is ready for review, such as tests passing, documentation updated, or a feature flag in place.
- Style and testing instructions, including the formatter or linter the team runs, the commands for the unit and integration suites, and where new tests belong.
- Code ownership information, so the hire can see which people or teams own each directory and who should review changes there.
- A hands-on walkthrough of the pull request workflow, done on a throwaway branch: create a branch, open a draft pull request, request a reviewer, respond to a comment, push a follow-up commit, and mark a thread resolved. Use your own platform’s labels; the goal is that the hire has performed each step once before doing it on real work.
Google’s secure and reliable systems guidance (Google, “Building Secure and Reliable Systems,” Chapter 21) recommends documenting peer review practices and educating new developers about expectations, including during onboarding to an organization or project. It also recommends clear guidelines for when a review should be lightweight and when it should be heavyweight. If your team does not have these written down, the new hire’s first review is the moment to create them.
Choose the first change and the reviewer
Pick a first change with bounded scope
The first change should be small enough that a reviewer can read it in one sitting and large enough to touch the real workflow. Good candidates include:
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- A bug fix in a module with good test coverage and a clear reproduction.
- A small feature addition behind an existing pattern, such as a new field on an established endpoint.
- A test-only change that adds coverage for behavior the team already relies on.
- A documentation or internal tooling fix that exercises the full review cycle without touching production paths.
Avoid a first change that modifies authentication, data migrations, payment logic, or shared infrastructure, and avoid one that depends on knowledge of several services. Those areas carry risk that is hard to judge without context, and the hire’s first review then becomes a review of the risk instead of a lesson in the code.
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 who responds within a reasonable period. For a new hire, add two more criteria. The reviewer should know the code area being changed, and the reviewer should be willing to explain the reasons behind standards rather than only pointing at them. The Google guide’s point that review can teach a language, framework, or design practice applies most strongly when the reviewer can explain the context.
Name one primary reviewer who owns the explanation and, if the team’s rules require it, a second reviewer for the area’s owners. Tell both reviewers that the first change is a learning exercise, so they know to write explanatory comments and to leave time for a short call if the discussion stalls.
What a new hire should look for in a review
The question of what a new hire should look for applies in two directions: when their own code is reviewed, and when they review someone else’s work. In both cases, the reviewer criteria in Google’s engineering practices guide give a practical checklist. The guide names design, functionality, complexity, tests, naming, comments, style, and documentation as the dimensions a reviewer considers. Add any team-specific security or reliability requirements to that list.
When the hire’s own change is reviewed
- Design: does the change fit the existing structure, or does it introduce a second way of doing the same thing?
- Behavior: does it do what the description says, including error paths and edge cases?
- Complexity: could a teammate understand this in six months without the author present?
- Tests: do the tests fail without the change and pass with it?
- Naming, comments, and documentation: do names describe what the code does, and do comments explain why rather than restating what the code says?
- Team requirements: does the change meet the team’s security, logging, and reliability rules?
When the hire reviews someone else’s change
A newer engineer can add real value by reviewing for clarity and tests, even before they know the subsystem well. A reasonable rule is that the hire comments on what they understand and says plainly what they do not. A comment such as “I don’t know this module well enough to judge the concurrency here; the test for the empty-queue case is unclear to me” is useful to the author and teaches the hire to mark the edge of their knowledge. Keep the hire’s approval for areas where the team has said they are ready to sign off.
Give feedback a new engineer can act on
Feedback works best when each comment follows the same pattern: describe the issue, explain why it matters, and state a concrete next step. Label optional suggestions clearly so that the hire can tell required changes from preferences. Invite questions, and when a comment depends on a local convention, name the convention and point to where it is written down.
Here is an example of a pair of comments on the same change. The code and names are illustrative, not from a real codebase:
- Required: “This loop calls the database once per item. With the batch sizes our nightly job uses, that adds latency and load. Next step: fetch the rows once before the loop and index them by ID. Our guide on data access covers this pattern.”
- Optional: “Nit, optional:
xcould beretryCount. Happy to leave this as is if you prefer the shorter name. Let me know if you want to talk through it.”
The required comment says what must change and why. The optional comment tells the hire they can decline it without an argument. Both invite a reply.
Google’s guide frames the goal as continuous improvement rather than perfection. A change should be approved when it improves the overall health of the code, even if it is not the reviewer’s ideal version. For a new hire, that means reviewers should avoid stacking dozens of optional points on a first change, because the hire cannot tell which ones matter.
Set review speed and response expectations
Google’s speed guidance states that one business day is the maximum response time in Google’s practice, and it advises reviewers not to interrupt focused tasks to handle reviews. That is Google’s norm, not an industry standard. Your team should choose its own target and publish it in the review guide. A first review should usually get a faster response than a routine change, because the hire is waiting on feedback to learn the workflow and may stall without it.
The table below lists the factors that change how much review a change needs. Use it to decide when a first review can be lighter and when it needs an extra reviewer or a live walkthrough.
| Factor | Review can be lighter | Add a reviewer or a heavier pass |
|---|---|---|
| Familiarity with the codebase and tooling | The hire has completed the workflow walkthrough and has shipped a prior small change | The hire has not yet run the test suite or navigated the module |
| Risk and scope of the change | Documentation, test-only, or a contained bug fix with clear behavior | Changes touching data integrity, authentication, billing, or shared infrastructure |
| Reviewer expertise in the affected area | The primary reviewer owns the module | The reviewer is outside the module and needs a second opinion from an owner |
| Team approval and ownership rules | Your written rules allow one approver for this path | Your written rules require owner approval for the directory changed |
| Explanation the hire needs to act on feedback | The hire asks specific questions and resolves comments without help | Comments repeatedly go unresolved or are answered with the same question |
Sources support adapting review to familiarity, risk, and expertise. They do not establish a universal reviewer count or approval policy, so the thresholds in your team’s guide should come from your own ownership rules.
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Before the hire’s first change is merged, confirm three things in the review thread:
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- What approval means. On your team, approval may mean the reviewer has checked the listed change, not that they endorse every decision in the design. Say so explicitly so the hire does not read a sign-off as a grade.
- Who can approve. Name the owners for the changed area, and say whether a single approval is enough or whether an owner must approve.
- How follow-up changes are reviewed. Decide whether the same reviewer re-reviews the changed lines, or whether the full diff is reviewed again, and state it before the first comment round begins.
Also say where unresolved questions go. A comment thread is good for code-level questions. Design questions, disagreements about team practice, and anything that would take more than a few exchanges belong in a short call, a team channel, or the design document. Tell the hire which of these to use, so a stalled thread does not become a silent stall.
Google Cloud’s onboarding description includes a requirement that new engineers receive extra approval for individual changelist submissions. That is a policy specific to Google’s own onboarding process, and it should not be copied as a general rule. If your team wants a similar step, make it a time-limited measure with a clear end point, such as a fixed number of changes or a set period, and document who grants the exception.
Calibrate for experience and risk
Calibration is the ongoing part. The first review sets the pattern, but the hire’s experience changes quickly over the first few months. Revisit the review settings at a fixed point, such as the end of the first month, and ask three questions: whether the hire now completes the workflow without help, whether their changes need fewer rounds of comments, and whether any area they touch still needs an owner’s approval that the team could now relax. Adjust one setting at a time so the effect is clear.
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Google Developers Blog, in a 2022 post titled “Using research to make code review more equitable,” gave an estimate that more than 1,000 engineer hours per day were lost to excess cost from interpersonal pushback during code review at Google. That figure is Google’s own internal estimate for its company. It is not an industry-wide measurement, and it should not be used to size the cost of review at another organization.
A Google Research case study on practice-based learning describes how new engineers became productive in Google’s codebase. It is a historical account of one large organization. It supports the idea that structured, hands-on practice helps new engineers, but it does not give a benchmark for onboarding time or productivity at other companies.
No general onboarding time, productivity gain, or first-change success rate is established by the sources in this area. If your team wants those numbers, measure them locally: track the time from the hire’s first pull request to merge, the number of review rounds on early changes, and how often the same comment category recurs.
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