Use the LLM playground to test your server against different LLMs. This is helpful to simulate how LLMs interpret your server and test for hallucinations. The playground is also great for simulating agent behaviors. You can customize the system prompt, swap models, and configure system prompts and temperature as if you would building an agent.
MCPJam Inspector Logo

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Set up LLM Playground

You need to set up at least one LLM to use the playground. Go to the settings tab in the inspector and follow instructions from there.

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OpenAI

Get an API key from OpenAI Platform. gpt-4o, gpt-4o-mini, gpt-4-turbo, gpt-4, gpt-5, gpt-4.1, gpt-4.1-mini, gpt-4.1-nano, gpt-3.5-turbo,o3-mini, o3, o4-mini, o1

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Claude (Anthropic)

Get an API key from Anthropic Console. claude-opus-4-0, claude-sonnet-4-0, claude-3-7-sonnet-latest, claude-3-5-sonnet-latest, claude-3-5-haiku-latest

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Gemini

Get an API key from Google AI Studio gemini-2.5-pro, gemini-2.5-flash, gemini-2.5-flash-lite, gemini-2.0-flash-exp, gemini-1.5-pro, gemini-1.5-pro-002, gemini-1.5-flash, gemini-1.5-flash-002, gemini-1.5-flash-8b, gemini-1.5-flash-8b-001, gemma-3-2b, gemma-3-9b, gemma-3-27b, gemma-2-2b, gemma-2-9b, gemma-2-27b, codegemma-2b, codegemma-7b

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Deepseek

Get an API key from Deepseek Platform deepseek-chat, deepseek-reasoner

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Ollama

Make sure you have Ollama installed, and the MCPJam Ollama URL configuration is pointing to your Ollama instance. Start an Ollama instance with ollama serve <model>. MCPJam will automatically detect any Ollama models running.

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Choose an LLM model

Once you’ve configured your LLM API keys, go to the Playground tab. On the bottom near the text input, you should see a LLM model selector. Select the model from the ones you’ve configured
Model selector

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System prompt and temperature

You can configure the system prompt and temperature, just like you would building an agent. The temperature is defaulted to the default value of the LLM providers (Claude = 0, OpenAI = 1.0).
Higher temperature settings tend to hallucinate more with MCP interactions
Model selector

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Elicitation support

MCPJam has elicitation support in the LLM playground. Any elicitation requests will be shown as a popup modal.