Backend Engineering 🛠

Level 1


Learns to write correct Go code, following guidance and training materials

Fixes simple bugs


Delivers assigned tasks, working with a more senior team member, and able to take PR feedback to improve their work


Improves documentation that is incorrect

Communication & Feedback

Provides regular status updates to their mentor/buddy

Points out syntactical improvements in code reviews

Writes PR descriptions that provide basic context for the change

Seeks guidance from other engineers, rather than answers


Level 2


Writes correct Go code following accepted best practices

Follows our Coding Conventions & Best Practices, uses language-level primitives correctly

Uses appropriate algorithms and data structures to solve problems

Writes automated unit and acceptance tests

Implements simple RPC handlers


Basic CRUD handlers

Internal/external API proxies

Designs simple database tables

Implements asynchronous messaging between services

Deploys services to staging and production

Handles simple error cases in RPC handlers and message consumers

Fixes bugs involving a number of services and can investigate production issues


Delivers assigned tasks that meet expected criteria

Works for the team, focuses on tasks that contribute to team goals

Tries to unblock themselves first before seeking help

Manages their own time effectively, prioritises their workload well, on time for meetings, aware when blocking others and unblocks

Helps the team, does what needs doing

Breaks down small/medium problems into iterative steps


Proactively raises issues they spot in retrospectives

Communication & Feedback

Proactively communicates to their team what they are working on, why, how it's going and what help they need

Accepts feedback graciously

Gives feedback to peers when asked

Provides helpful and actionable feedback in code reviews in an empathetic manner

Take a look at the levelling up your code reviews talk for some ideas

Writes PR descriptions that provide context and provide rationale for significant decisions

“I decided to X instead of Y here, I also considered Z but for these reasons I went with X”


Level 3


Writes idiomatic Go code

Follows the guidelines in Effective Go, avoids using patterns that are idiomatic in other languages

Uses appropriate design patterns

Implements complex RPC handlers

Implements complex business logic, orchestrates multi-stage processes, deals with idempotency or distributed data sources

Designs new schemas comprising multiple tables

Implements complex asynchronous messaging flows

Co-ordinates complex deployments and database migrations

Implements distributed systems consisting of multiple interacting services

Produces technical designs that include a consideration of scalability

Handles complex error cases in RPC handlers and message consumers

Mitigates race conditions and partial failure states in distributed systems

Uses locking where appropriate, writes code that is “self-healing” when dealing with distributed failure (e.g. data needs to be written in two or more services)

Debugs production issues

Considers metrics when building a new system


Delivers large well-defined tasks and solves small scope not-well-defined problems

Contributes to writing proposals (Co-authors with more experienced Engineer)

Breaks down large problems into smaller iterative steps across multiple PRs


Provides valuable input to proposals from their team

Proactively improves modules, services, systems and codebases they encounter, 'this doesn't make sense, I'm going to do something about it'

Contributes to scaling engineering hiring (e.g. leads calls, does onsite interviews)

Builds simple tools or iterates existing tools for the benefit of all engineers

Communication & Feedback

Transparent about mistakes they've made, early

Proactively gives timely actionable feedback to peers

Proactively seeks feedback from the people around them

Considers the opinions of others before defending their own


Onboards / mentors new engineers

Finds learning opportunities for others when reviewing their code and follows it up

“I think this code could be improved by doing X, let’s pair on it and I’ll talk through why X is good for this”

Level 4


Writes code that serves as a definitive example for new engineers

Makes contributions to library code or core services

Bug fixes, small improvements; things that don’t result in a major change in the public API

Builds systems that scale reliably without intervention

Services can withstand a year’s worth of growth in load/user base without needing first aid

Leads the refactoring (de-cruftification) of complex systems

Debugs complex production issues at speed

Identifies and fixes security vulnerabilities

Identifies and fixes performance bottlenecks in individual services

Explains all aspects of the platform to new engineers

Implements services or libraries that require a deep level of domain knowledge


Mastercard message parsing

Credit decisioning

CASS scheduling

Google Pay

Includes actionable dashboarding as part of a new system


Solves ambiguous problems

Leads writing small/medium scope proposals

Thrown at fires and resolves / contributes heavily to resolving them

Makes pragmatic choices about taking on tech debt

Considers multiple different solutions for solving a problem

Breaks down projects into smaller iterative steps that each deliver value


Positively influences engineers in the wider org

Maintains documentation on things they know the most, makes it easy for future engineers to interact with systems/code

Clears blockers for junior team members, provides context/guidance, or knows how to escalate

Asks why. Does not take truths for granted unless they understand exactly where they are coming from (especially with regards to regulation, compliance, etc)

Drives changes to engineering practices with well-reasoned arguments and a "strong opinion, weakly held" mentality

Shapes the direction of systems designs with less experienced engineers

Breaks down delivery and knowledge silos in their squad

Communication & Feedback

Proactively gives feedback "upwards" and to people they interact with who are not in their team

Transparent in making design and technical decisions

Helps people in non-technical roles understand technical constraints / trade-offs

Shares technical context and direction for less experienced engineers

Gives direct and constructive feedback to other engineers


Contributes to maintaining the Monzo culture in their team, helping new joiners

Gets buy-in on technical decision-making and proposed designs

Proactively involves other relevant engineers

Sought out for code reviews

Instils Monzo engineering principles in other engineers

Helps the growth of engineers around them through coaching and mentoring

Helps their squad work together more effectively

Helps facilitate team/squad rituals

Makes improvements to modules/libraries/services and goes out of their way to help others learn from it

“I’ve used RxJava for the first time here, I’m going to do a talk about why I’ve done this, here’s some great blog posts on it”

Level 5


Builds systems that serve as definitive examples for new engineers

Makes major contributions to library code or core services

Contributes to external technologies or libraries that we depend on

Produces clear technical designs for large complex projects


Outbound and Inbound MasterCard clearing proposals

Develops clear technical solutions from ambiguous requirements

Uncovers and fixes tricky bugs that have previously evaded detection

Implements security improvements that impact multiple services

Implements performance improvements that impact multiple services

Demonstrates a deep level of knowledge in a specific area

Serves as a technical authority on a technology or an area of the codebase

Creates dashboards that broadly impact all engineers


Solves the 'hard problem' in a project e.g. Mastercard crypto and sees it through to resolution

Solves larger ambiguous problems

Leads incident resolutions

Makes judgements about when to diverge from the immediate goal to achieve something else

Leading large scale technical infrastructure projects (level 5 would originate or complete, probably)

Leads writing large scope proposals

Breaks down large long-lasting projects into sensible discrete chunks that compound to achieve a large goal

Helps prioritise and balance short-term and long-term investments, focusing on high impact, high value work


Represents Monzo at conferences/events

Given as reason for other engineers to join Monzo

Proactively shares knowledge internally

Acts as the 'sole proprietor', in the CEO mindset, their ego/agenda is not a factor in their thinking or decision making

Communication & Feedback

Helps other people develop themselves and regularly gives insightful, useful feedback to those around them.

Talks to non-technical stakeholders on appropriate level of abstraction


Instils Monzo engineering principles across a whole squad of engineers

Works with relevant Engineering Managers to help other engineers perform and grow

Fosters effective collaboration in multi-disciplinary squads (backend, mobile, data, design, web)

Delegates technical decisions with low risk and high reversibility

Owns technical decisions with high risk and low reversibility

Contributes to maintaining the Monzo culture in the wider company

Bootstraps new teams

Level 6


Makes major contributions to technologies and libraries that we depend on

Makes improvements to the stability, performance or security of the entire platform

Serves as a technical authority in the wider engineering community


Accountable for delivery of large, mission critical engineering projects

Originates or finishes large, horizontal engineering efforts


Attracts other very senior hires

Engineers around them get better and have a bigger impact, faster

Communication & Feedback

Transparent about feedback they have received and what they are going to do differently


Helps groups of squads work together more effectively

Starts things that they cannot finish by themselves

Delegates to make better use of their time