LLM Test Server

LLM Test Server is a deterministic LLM API mock server for .NET and Aspire.

LLM Test Server is a deterministic LLM API mock server built for .NET, Aspire, and any language that speaks HTTP. It allows developers to script responses, streaming, tool calls, and failures, enabling applications to make real HTTP or SDK calls against a local server. The tool supports thirteen provider API families including OpenAI, Anthropic, Gemini, and Azure OpenAI, each under its own local namespace. A built-in request dashboard displays traffic insights, token usage, latency, and wire payloads for thorough debugging. It is designed for developers who want to test conversation flows and handle provider interactions deterministically without relying on live models.

LLM Test Server at a glance

Best for: Software engineer
Runs on: Web, self-hosted, API, Docker
Pricing: Free
Released: October 2026
Category: AI coding tool
Website: llmtest.managed-code.com

Key features

Script model responses, streaming, tool calls, and failures
Inspect requests and token usage with a built-in dashboard
Support thirteen provider API families locally
Run tests in parallel with separate session states
Analyze input token composition and prompt caching
Verify conversation graphs and tool loops step by step

Use it for

Test LLM application behavior deterministically
Inspect request payloads and token distribution
Simulate provider failures and rate limits
Run multi-turn conversation and tool loops

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