As a Software Engineer at Tessian, you are stepping into a role that is central to the company’s mission: securing the "Human Layer." While traditional security tools focus on networks and devices, Tessian uses machine learning to protect people from mistakes—like sending an email to the wrong person or falling for a sophisticated phishing attack. Your work directly impacts the safety of enterprise data across the globe.

In this position, you will work on high-scale systems that process millions of emails and events in real-time. You will tackle complex engineering challenges involving low-latency data processing, distributed systems architecture, and the integration of predictive models into production environments. Whether you are focused on the backend infrastructure or the user-facing dashboard, your code must be robust, secure, and performant.

This role requires more than just coding ability; it demands an engineering mindset that prioritizes reliability and user empathy. You will join a collaborative engineering culture where technical rigor meets creative problem-solving. You are expected to take ownership of your features from design to deployment, ensuring that Tessian remains the market leader in Human Layer Security.

The following questions are representative of what candidates have encountered at Tessian. They are not guaranteed to appear but serve as excellent practice for the types of problems you will solve.

Technical & Coding

This category focuses on your ability to write correct, working code, often involving logical parsing.

• "Evaluate a mathematical expression given in prefix notation (e.g., + * 2 3 4)."
• "Implement a function to evaluate a postfix expression (Reverse Polish Notation)."

These questions are based on real interview experiences from candidates who interviewed at this company. You can practice answering them interactively on Dataford to better prepare for your interview.

Preparation for Tessian requires a balance of algorithmic fluency and pragmatic system design skills. The process is designed to test your raw coding ability as well as your capacity to collaborate on complex technical problems.

Key Evaluation Criteria:

• Algorithmic Correctness & Code Quality – Tessian places a high premium on writing clean, correct code. During the initial screening and technical rounds, "getting it working" is not enough; your solution should handle edge cases gracefully and demonstrate a strong grasp of data structures.
• Technical Communication – In the "Code Pair" rounds, you are evaluated on how well you articulate your thought process. Interviewers want to hear why you chose a specific approach or library, not just see the syntax on the screen.
• System Design & Scalability – For mid-to-senior roles, you must demonstrate an understanding of how to build systems that scale. You will be assessed on your ability to design architectures that can handle high throughput and ensure data consistency.
• Culture & Mission Alignment – Tessian looks for engineers who are curious, autonomous, and passionate about the product. You should be ready to discuss your motivations and how you align with the goal of empowering people to work securely.

The interview process at Tessian is streamlined but rigorous, typically taking 2–4 weeks from application to offer. It almost always begins with an automated technical assessment, which serves as a gateway to the interactive rounds. The company values efficiency, so expect quick turnarounds between stages if you are successful, though candidates are advised to follow up if communication stalls.

You will first encounter a HackerRank assessment. This is a critical filter; the problems often focus on data manipulation and parsing logic rather than obscure dynamic programming riddles. Accuracy and passing all test cases are prioritized over speed. Following a successful test, you will move to a recruiter screen to discuss your background and interest in the role.

The core of the process involves live technical interactions. This usually includes a "Code Pair" interview where you solve problems alongside an engineer, often building upon concepts from the initial test or tackling new practical scenarios. The final stage is a "Virtual Onsite" loop, comprising deep-dive technical sessions (coding and system design) and a behavioral interview, often with the Head of Engineering or a senior leader, to assess your potential for long-term impact at the company.

Understanding the Timeline: This timeline reflects a standard flow. The HackerRank stage is the most common stumbling block; ensure you have a block of uninterrupted time to complete it. The final "Virtual Onsite" is intense, often bundling 2–3 interviews into a single block, so manage your energy accordingly.

Coding & Algorithms

This is the most heavily weighted area in the early stages. Tessian relies on HackerRank and live coding to ensure you have strong foundational skills. The questions often involve parsing strings, evaluating mathematical expressions, or manipulating lists and dictionaries.

Be ready to go over:

• String Manipulation & Parsing – Evaluating prefixes/postfixes, implementing calculator logic, or parsing custom data formats.
• Data Structures – Proficient use of Stacks, Queues, Hash Maps, and Trees.
• Python Proficiency – Python is the primary language for these tests. You should know the standard library inside out (e.g., collections, itertools).
• Edge Case Handling – Handling empty inputs, malformed strings, or large datasets without crashing.

Example questions or scenarios:

• "Implement a parser that evaluates a mathematical expression in postfix notation."
• "Given a list of email logs, filter and aggregate them based on specific security rules."
• "Solve a problem involving stack-based evaluation of prefixes."

System Design & Architecture

In the final rounds, especially for senior roles, you will face system design questions. These discussions assess your ability to build the infrastructure that powers Tessian.

Be ready to go over:

• High-Volume Data Ingestion – Designing systems that can process millions of emails with minimal latency.
• Microservices Architecture – Breaking down a monolithic problem into scalable services.
• Database Design – Choosing between SQL and NoSQL for specific use cases (e.g., storing user profiles vs. storing event logs).
• Cloud Native Concepts – Familiarity with AWS services (Lambda, Kinesis, DynamoDB) is often tested implicitly or explicitly.

Example questions or scenarios:

• "Design a system that detects and flags phishing emails in real-time."
• "How would you architect a service to handle a sudden 10x spike in email traffic?"

Collaboration & Behavioral

Tessian values engineers who can communicate complex ideas simply. The "Values" interview is not a formality; it determines if you will thrive in their environment.

Be ready to go over:

• Project Deep Dives – Explaining a past technical challenge, the trade-offs you made, and the outcome.
• Feedback & Growth – How you handle code reviews and technical disagreements.
• Motivation – Why security? Why Tessian?

Example questions or scenarios:

• "Tell me about a time you disagreed with a product manager on a technical requirement."
• "Describe a complex technical concept to someone without a technical background."