Airtable·Software Engineer·Onsite - System Design / Architecture·Senior

Senior

Jul 2026

Summary

Airtable system design round for a software engineer role. The question was a deep dive into JSON serialization with circular references, which sounds manageable until you realize they want you to cover basically every edge case imaginable in one go.

Questions Asked (1)

Design a JSON serialization and deserialization strategy that handles circular references between objects. Cover cycle detection, stable object identifiers, preventing infinite recursion, preserving shared subobjects, traversal order choices, determinism, support for primitives and dicts, input validation and security, and cross-language compatibility. Also analyze time and space complexity and compare alternative approaches like reference tables or anchor/alias schemes.

System DesignTechnical Trade-offsAlgorithms & Data Structures

Author's notes

This question is basically five questions welded together.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a reference-based serialization scheme with stable IDs and a visited set to handle cycles. Walk through the algorithm, covering traversal, determinism, validation, and cross-language compatibility, and analyze complexity and alternatives.

Pro tip: Emphasize determinism and security: use stable IDs and canonical ordering to ensure reproducible output, and validate inputs to prevent injection or resource exhaustion. Mention that this approach is used in production systems like Protocol Buffers and GraphQL.

1. Clarify Requirements and Constraints

Ask about expected object types, size, performance needs, and cross-language requirements to tailor the solution.

2. Design the Serialization Scheme

Propose a format with a reference table mapping stable IDs to objects, and a visited set to detect cycles and preserve shared subobjects.

3. Define Traversal and Determinism

Choose a traversal order (e.g., depth-first) and ensure deterministic output by sorting keys or using stable IDs.

4. Address Validation, Security, and Compatibility

Include input validation, size limits, and a language-agnostic format (e.g., JSON with $ref) for cross-language support.

5. Analyze Complexity and Alternatives

Discuss time/space complexity (O(n) with hash map) and compare with anchor/alias schemes or reference tables.

Key Points to Mention

Cycle detection using a visited set or reference table with stable IDs.
Preserving shared subobjects by referencing the same ID.
Determinism via canonical ordering and stable ID assignment.
Input validation and security: depth limits, size limits, and avoiding code execution.
Cross-language compatibility using a standard format like JSON with $ref or $id.
Time and space complexity: O(n) time and space with hash map, and comparison to alternatives like anchor/alias.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.