What is a Software Engineer at Tessian?

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.

Getting Ready for Your Interviews

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.

Interview Process Overview

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.

Deep Dive into Evaluation Areas

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."

Key Responsibilities

As a Software Engineer at Tessian, your daily work revolves around building and maintaining the intelligence behind the platform. You are responsible for writing production-grade code that integrates seamlessly with the company's machine learning models. This often involves working on backend services that sit directly in the flow of enterprise email traffic, meaning stability and speed are non-negotiable.

You will collaborate closely with Data Scientists to operationalize their models. While they build the algorithms to detect anomalies, you build the infrastructure that serves these predictions at scale. You will also work with Product Managers and Designers to ensure that security warnings and dashboards are intuitive for end-users.

Beyond coding, you are expected to contribute to the engineering culture. This includes participating in rigorous code reviews, writing design documentation (RFCs), and mentoring junior engineers. You will frequently troubleshoot production issues, requiring a deep understanding of the full stack—from the database layer up to the API endpoints.

Role Requirements & Qualifications

To succeed in this process, you need a solid technical foundation and a willingness to work in a Python-centric environment.

Must-have skills:

• Strong Coding Ability: Proficiency in a modern programming language is essential. Python is heavily preferred for interviews and daily work, though Java or C++ backgrounds are acceptable if you are willing to switch.
• Algorithmic Foundations: A solid grasp of Big O notation, data structures, and algorithms.
• Communication: Ability to articulate technical decisions clearly in English.
• Web Technologies: Understanding of HTTP, REST APIs, and basic networking principles.

Nice-to-have skills:

• Cloud Experience: Hands-on experience with AWS (EC2, ECS, Lambda).
• Frontend Frameworks: Experience with React is a significant plus for full-stack roles.
• Security Domain Knowledge: Familiarity with email protocols (SMTP) or general cybersecurity concepts.

Common Interview Questions

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)."
• "Write a program to simulate a simple calculator that respects order of operations."
• "Given a set of email rules, determine if a specific email should be blocked or allowed."
• "Find the first non-repeating character in a stream of characters."

System Design

• "Design a URL shortening service that scans for malicious links."
• "How would you design the backend for an email archiving system that needs to be searchable?"
• "Architect a real-time notification system for a security dashboard."

Behavioral & Values

• "Why do you want to work in the email security space?"
• "Tell me about a time you had to learn a new technology quickly to solve a problem."
• "What is the most technically challenging bug you have ever fixed?"
• "How do you prioritize code quality versus delivery speed?"

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.

Frequently Asked Questions

Q: Which programming language should I use for the HackerRank and coding rounds? Tessian is primarily a Python shop. While you may be allowed to use other languages in the initial HackerRank, using Python is strongly recommended. It aligns with their stack and allows interviewers to better evaluate your code quality during live pair programming sessions.

Q: Is the work environment remote or in-office? Most recent interview experiences indicate a fully remote or hybrid interview process. Tessian supports flexible working arrangements, but specific expectations may vary depending on whether you are applying for a role based in London, the US, or remotely. Clarify this with your recruiter early on.

Q: How difficult is the HackerRank test? The difficulty is generally described as "Medium." It is not typically about solving an obscure dynamic programming puzzle but rather about implementing a logical solution correctly. Candidates often fail because they miss edge cases or their code is "partially correct." Focus on passing all test cases rather than finishing quickly.

Q: What happens if I don't hear back after the test? Unfortunately, some candidates have reported delays or lack of feedback after the HackerRank stage. If you do not hear back within 5–7 business days, send a polite follow-up to your recruiter.

Q: Does Tessian ask LeetCode-style questions? Yes, but they lean towards practical data manipulation (strings, stacks, parsing) rather than abstract graph theory. Questions involving "prefix/postfix evaluation" are historically common.

Other General Tips

• Master the "Why": In the Code Pair round, silence is a red flag. Narrate your thinking. If you are using a Python dictionary, explain why it is better than a list for that specific operation (e.g., O(1) lookups).
• Review Stack-Based Problems: A significant number of candidates report questions involving expression evaluation (calculators, prefix/postfix). Reviewing how to use Stacks for these problems is high-yield preparation.
• Check Your Environment: The Code Pair tool is often browser-based. Ensure you are comfortable coding in a simple IDE without heavy reliance on autocomplete. One candidate reported losing power during a test—have a backup plan if possible!
• Know the Company Product: Read about "Human Layer Security." Understanding that they filter outbound emails for errors (not just inbound spam) shows you understand their unique value proposition.
• Ask Insightful Questions: In the final round with Engineering leadership, ask about the challenges of scaling their ML models or how they handle false positives. This demonstrates deep engagement with the engineering challenges.

Summary & Next Steps

Interviewing for a Software Engineer role at Tessian is an opportunity to join a team tackling some of the most critical security challenges in the modern enterprise. The process is designed to identify engineers who are not only technically proficient in Python and system design but also passionate about protecting users. By focusing your preparation on data structure fundamentals—specifically parsing and stack-based logic—and practicing your ability to articulate your design choices, you will be well-positioned to succeed.

Approach the technical screens with a focus on correctness and clarity. The team wants to see that you can write code that is robust enough for a security product. In the behavioral rounds, let your genuine interest in the product and your collaborative nature shine through. This is a chance to work on high-impact systems; show them you are ready for the responsibility.

Interpreting the Data: The salary figures provided reflect the competitive nature of the security software market. Compensation packages at Tessian typically include a mix of base salary and equity (stock options), rewarding long-term impact. Be prepared to discuss your expectations during the recruiter screen, keeping in mind that total compensation often scales significantly with seniority and location.

For more detailed interview insights and resources to help you practice, visit Dataford. Good luck with your preparation!