Senior .NET Backend Engineer – Minimal API

Location: Toronto, ON

Work Model: Hybrid – 2 days onsite per week in downtown Toronto

Client - Deloitte, vendor – improving

We are seeking a Senior Backend Engineer specializing in modern .NET / C# API development, with explicit experience building APIs using the .NET Minimal API architecture.

This role focuses on high-performance backend services, modern C# coding patterns, strong resiliency design, and secure coding practices.

Candidates with large-scale SaaS experience or prior Microsoft background are particularly attractive.

This is not a legacy .NET developer role.

We specifically want engineers who have worked with modern ASP.NET Core patterns, including Minimal APIs, modern dependency injection, and modern C# language features.

who have only worked in:

legacy .NET Framework

WebForms

traditional MVC controller-heavy architectures

may not be a fit unless they also demonstrate experience with modern .NET API architecture.

Mandatory Skill Area 1 – Minimal API Experience

This is the most important requirement.

The engineer must have experience building APIs using .NET Minimal APIs, which are a lighter-weight alternative to traditional ASP.NET MVC controllers.

Minimal APIs were introduced in .NET 6+ and are now widely used in modern microservice architectures.

Look for any of the following phrases:

Direct Terms

Minimal API

.NET Minimal APIs

ASP.NET Core Minimal APIs

Equivalent Descriptions

Controller-less APIs

Lightweight ASP.NET APIs

Endpoint-mapped APIs

Functional endpoint APIs

Code-first APIs

Minimal hosting model

Top-level program APIs

Code signals that strongly suggest Minimal API experience

Mandatory Skill Area 2 – Advanced C# / .NET Expertise

The engineer must be very strong in modern C# and .NET Core development.

Look for candidates with experience in:

• ASP.NET Core
• .NET 6 / .NET 7 / .NET 8
• backend service architecture
• REST API development
• They should demonstrate familiarity with modern C# language features, including:
• file-scoped namespaces
• global using directives
• top-level programs
• async/await patterns
• dependency injection
• modern logging frameworks

Mandatory Skill Area 3 – Error Handling & Resiliency

This role requires strong understanding of production-grade backend systems.

Candidates should demonstrate experience implementing:

Error Handling Strategies

Examples:

centralized exception handling

middleware-based error pipelines

structured logging

graceful error responses

Resiliency Patterns

Look for experience with patterns such as:

retries

circuit breakers

timeouts

fallback mechanisms

fault isolation

Candidates who mention tools such as Polly or resilience libraries are often strong fits.

Mandatory Skill Area 4 – Performance Optimization

Candidates should have experience optimizing high-throughput backend services.

Examples may include:

• reducing API latency
• optimizing database calls
• caching strategies
• improving concurrency performance
• tuning memory allocation
• async architecture
• Mandatory Skill Area 5 – Secure C# Development
• The engineer must demonstrate secure coding practices in .NET.

Key areas include:

Input Validation

preventing injection attacks

validating external data

Encryption

symmetric / asymmetric encryption

protecting sensitive data

Hashing

password hashing

secure hashing algorithms

Secrets Management

environment secrets

cloud key vault systems

secure configuration management

Nice-to-Have Signals

These are not required but very attractive.

Previous experience working at Microsoft

Experience with large SaaS platforms

Experience building cloud-native APIs

Microservice architectures

Kubernetes-based deployments.