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The Expect API is your Swiss Army knife for MCP testing. Use it to assert everything from simple content checks to complex path efficiency and LLM quality judgments.

Quick reference

The Expect namespace provides intuitive access to all evaluator factories:

Content namespace

Validate the actual text content returned by your agent:

Basic content checks

Advanced content patterns

Tools namespace

Verify tool usage patterns and success rates:

Basic tool checks

Tool sequences and patterns

Tool output validation

Performance namespace

Ensure your agent meets performance requirements:

Response time and efficiency

Resource usage

Judge namespace

Use LLM judges for nuanced quality evaluation:

Simple rubric evaluation

Multi-criteria evaluation

Custom judge configuration

Path namespace

Enforce optimal execution paths:

Golden path enforcement

Flexible path checking

Combining assertions

Create comprehensive test scenarios by combining multiple assertions:

Best practices

Start simple, then add complexity: Begin with basic content assertions, then layer on tool checks, performance requirements, and quality judgments as needed.
Avoid over-constraining: Too many strict assertions can make tests brittle. Focus on what truly matters for your use case.
Use descriptive names: Always provide a name parameter for your assertions. This makes debugging much easier when tests fail.

See also

Complete Assertions Reference

Every available assertion with examples

Custom Evaluators

Build your own domain-specific evaluators