# System Design Skills Test and Verified Score > A system design skills test built on realistic trade-offs, plus live design sessions with practitioners. Prepare for interviews and prove the skill. Source: https://getlemma.io/skills/system-design System design ability is almost impossible to read from a CV and hard to judge in one interview. Lemma records how you reason through designs over several live sessions, rated by practitioners who build these systems. How system design is assessed Preparing for an interview? [System design interview questions, junior to senior](https://getlemma.io/skills/system-design/interview-questions) ## What system design competence looks like A competent system designer starts with requirements, not boxes. They pin down what the system must do, how much traffic and data it will see in rough terms, and what consistency and latency the users actually need. Every component they add has a reason they can state in one sentence. They talk in trade-offs. They know what a cache buys and what it costs in staleness, when a queue decouples services and when it hides problems, and how a design behaves when a dependency fails. They change their design when a reviewer exposes a weakness, rather than defending the first sketch. ### Requirements and estimates Clarifying functional needs, rough traffic and storage estimates, and the constraints that shape the design. ### Data storage choices Relational, document and key-value stores, partitioning, replication and the trade-offs between them. ### Caching Where to cache, how to invalidate and what staleness the product can tolerate. ### Queues and async work Decoupling services, retries, idempotency and handling poison messages without losing data. ### Consistency and availability Reasoning about failure, network partitions and the consistency guarantees users actually need. ### Observability and failure Metrics, logs, traces, timeouts and graceful degradation when parts of the system fail. ## What counts as evidence of system design skills? Certificates in system design show an exam was passed. Lemma records how you work: sessions where you talked through a design or an incident, an adaptive test, and configuration in repositories you link. Every entry says where it came from. See the [evidence methodology](https://getlemma.io/methodology#evidence-types) for how each source is weighed. [Live session](https://getlemma.io/product/sessions) ### Designing a system live A practitioner gives you a product brief and plays the role of a reviewer. You gather requirements, sketch a design and defend trade-offs, and they rate how you reason. [Live session](https://getlemma.io/product/sessions) ### Teaching a design pattern Explaining a pattern such as a write-ahead log or a fan-out feed to another engineer shows depth. Teaching sessions count for more than learning ones in your record. [Adaptive assessment](https://getlemma.io/product/assessments) ### Scenario questions on trade-offs Adaptive questions describe realistic situations, such as a hot partition or a cache stampede, and ask for the best response. Difficulty rises or falls with each answer. [GitHub connector](https://getlemma.io/product/passport) ### Design docs or a service on GitHub Connect a repository with a service you designed or an architecture write-up. Lemma checks that it exists and that your account has access to it. ## How is a system design skills test run on Lemma? The system design test is adaptive, 15 to 25 questions on failure modes, permissions and cost rather than service names, and it stops once your level holds steady. With sessions and linked work it sets your system design SCI, where recent evidence carries more weight. [How the SCI score is calculated](https://getlemma.io/product/sci)[How adaptive skills assessments work](https://getlemma.io/product/assessments)[Practise system design in live skill swap sessions](https://getlemma.io/product/sessions)[Which evidence types count](https://getlemma.io/methodology#evidence-types)[What your Skills Passport shows](https://getlemma.io/product/passport) 1. ### Learn the building blocks The AI tutor quizzes you on caching, replication, queues and consistency, and asks you to explain trade-offs in your own words. Drills add only a small, capped amount to your practice score. 2. ### Run design sessions with peers Book live sessions where a practitioner gives you a brief and challenges your design. Several sessions with different reviewers build a stronger record than one long interview could. 3. ### Take the scenario assessment Answer adaptive scenario questions on storage, scaling and failure handling. Each question has a time limit, you cannot go back, and questions do not repeat, so the result reflects your judgement. ## System design skills: common questions ### How do I practise for a system design interview? Practise out loud with someone who pushes back. On Lemma, you book live design sessions with practitioners who give you a brief and challenge your trade-offs, then rate the session. Use the AI tutor to review building blocks between sessions, and take the scenario assessment to find gaps. ### How can senior engineers prove system design ability? Seniority is usually inferred from titles and years, which say little about design judgement. A record of live design sessions rated by different practitioners, plus an adaptive assessment, shows how you actually reason. Share it in your Skills Passport alongside any design documents you connect. ### What do reviewers look for in a system design session? They look for clear requirements, rough estimates, justified component choices and honest discussion of trade-offs and failure modes. They also watch how you respond to challenges. Changing a design when a weakness is exposed is a strength, not a mistake. ### Is system design only for backend engineers? No. Frontend, mobile, data and infrastructure engineers all make design decisions about state, caching, APIs and failure. The skill covers that shared reasoning. Evidence here pairs naturally with your main skill and shows you can think beyond a single component. ## Skills related to system design [Browse the skills directory](https://getlemma.io/skills) [### Cloud architecture Show how you design cloud systems that scale, fail gracefully and stay affordable. Evidence for cloud architecture](https://getlemma.io/skills/cloud-architecture)[### AWS Evidence that you can design, secure and run workloads on AWS, not just name services. Evidence for AWS](https://getlemma.io/skills/aws)[### DevOps Evidence of how you build pipelines, ship safely and keep systems observable. Evidence for DevOps](https://getlemma.io/skills/devops)[### Go Prove you write clear, concurrent Go services, with evidence from live code and connected repositories. Evidence for Go](https://getlemma.io/skills/golang) ![Painting of an olive grove in soft sunlight with hills beyond](https://cdn.sanity.io/images/islu4peo/production/613eb3f93566423c9adf45246f2cf1a61437c04c-1680x1120.jpg?w=1080&fm=webp&q=68&fit=max) ## Start your system design evidence record. Lemma is in early access. Request an invite and we will email you when your place is ready.