Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/gleanwork/mcp-server-tester/write-mcp-host-evalnpx skills add gleanwork/mcp-server-tester --skill write-mcp-host-evalgit clone --depth 1 https://github.com/gleanwork/mcp-server-testerWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/gleanwork/mcp-server-tester/write-mcp-host-eval)<a href="https://agentmods.dev/skills/gleanwork/mcp-server-tester/write-mcp-host-eval"><img src="https://agentmods.dev/badge/skills/gleanwork/mcp-server-tester/write-mcp-host-eval.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00064 | $0.04319 |
| Opus 5 | $0.00032 | $0.02159 |
| Sonnet 5 | $0.00013 | $0.00864 |
| Haiku 4.5 | $0.00006 | $0.00432 |
Grade A, and why
write-mcp-host-eval scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 563 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Write MCP Host Simulation Evals
Generate LLM host simulation evals for MCP servers using @gleanwork/mcp-server-tester. In mcp_host mode, a real LLM receives a natural language scenario and decides which MCP tools to call — testing tool discoverability, parameter clarity, and description quality.
When to Use mcp_host Mode
Use mcp_host mode when you need to verify:
- Does the LLM know which tool to call for a given task?
- Does the LLM fill in parameters correctly without hints?
- Does the tool description accurately represent what the tool does?
Use direct mode instead for:
- Regression testing known inputs/outputs (faster, free, deterministic)
- Testing tool logic and error handling
- Schema validation
mcp_host mode calls a real LLM API. Each test costs ~$0.003–0.02 depending on the provider and tool count.
Prerequisites
Install the Vercel AI SDK and your provider package:
# Pick your provider
npm install ai @ai-sdk/anthropic # Anthropic
npm install ai @ai-sdk/openai # OpenAI
npm install ai @ai-sdk/google # Google
npm install ai @ai-sdk/mistral # Mistral
npm install ai @ai-sdk/azure # Azure OpenAI
npm install ai @ai-sdk/deepseek # DeepSeek
npm install ai @ai-sdk/xai # xAI (Grok)
npm install ai @ai-sdk/google-vertex # Vertex AI (Anthropic models)
npm install ai @openrouter/ai-sdk-provider # OpenRouter
Set the corresponding API key environment variable (e.g., ANTHROPIC_API_KEY, OPENAI_API_KEY).
Step 1 — Understand the Case Structure
mcp_host cases differ from direct mode cases:
| Field | Direct mode | mcp_host mode |
|---|---|---|
mode |
"direct" (default) |
"mcp_host" (required) |
toolName |
Required | Not used |
args |
Required | Not used |
scenario |
Not used | Required — natural language prompt |
mcpHostConfig |
Not used | Provider, model, host type |
expect |
Response assertions | Tool call assertions + response assertions |
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 5d ago First seen · 563 lines · 64 tokens per session scan A b0370263bac2
write-mcp-host-eval is a skill published in the GitHub repository gleanwork/mcp-server-tester (19 stars, last pushed yesterday), licensed MIT. It adds 64 tokens to every session and 4,319 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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