microsoft/wassette is a runtime that loads WebAssembly Components as tools exposed through the Model Context Protocol (MCP), an interface that lets AI agents use external capabilities. It is for extending coding agents with reusable tools while isolating those tools in a Wasmtime security sandbox. The catalogue skills, instructions, and agent help configure and operate Wassette with supported MCP clients.
Borrowing it
Nothing to install: this file belongs to microsoft/wassette. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/microsoft/wassette/main/.agents/skills/mcp-inspector-testing/SKILL.mdgit clone --depth 1 https://github.com/microsoft/wassetteWrote 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/microsoft/wassette/mcp-inspector-testing)<a href="https://agentmods.dev/skills/microsoft/wassette/mcp-inspector-testing"><img src="https://agentmods.dev/badge/skills/microsoft/wassette/mcp-inspector-testing/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/microsoft/wassette/mcp-inspector-testing"><img src="https://agentmods.dev/badge/skills/microsoft/wassette/mcp-inspector-testing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 8 findings, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium MCP Rug Pull · line 39 npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.Fix: Pin the version: npx @scope/[email protected]
- medium MCP Rug Pull · line 40 npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.Fix: Pin the version: npx @scope/[email protected]
- medium MCP Rug Pull · line 41 npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.Fix: Pin the version: npx @scope/[email protected]
- medium MCP Rug Pull · line 44 npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.Fix: Pin the version: npx @scope/[email protected]
- medium MCP Rug Pull · line 48 npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.Fix: Pin the version: npx @scope/[email protected]
- medium MCP Rug Pull · line 50 npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.Fix: Pin the version: npx @scope/[email protected]
- medium MCP Rug Pull · line 54 npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.Fix: Pin the version: npx @scope/[email protected]
- medium MCP Rug Pull · line 61 npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.Fix: Pin the version: npx @scope/[email protected]
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 | $0.00058 | $0.00725 |
| Opus 5.5 | $0.00023 | $0.00290 |
| Sonnet 5.5 | $0.00012 | $0.00145 |
| Haiku 4.5 | $0.00006 | $0.00072 |
Grade A, and why
mcp-inspector-testing 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 2mo 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 — 75 lines — stays where its author put it; the contents beside it link to each section on GitHub.
mcp-inspector-testing skill
Test server-facing Wassette changes with the MCP Inspector before committing. This confirms the server starts, tools are exposed over MCP, tool calls behave as expected, and no regressions slipped in.
Workflow
- Build your changes:
just build. - Start the server (Terminal 1):
just run, or an example such asjust run-fetch-rs. The server listens at127.0.0.1:9001/mcpover Streamable HTTP. - Drive it with the Inspector (Terminal 2) — always run
tools/listfirst. - Capture Inspector output when it helps demonstrate or debug the change.
Running the server
just run # Default server
just run RUST_LOG='debug' # Verbose logs
just run-filesystem # Example: filesystem component
just run-fetch-rs # Example: fetch component
just run-memory # Example: memory component
just run-get-weather # Example: weather (needs OPENWEATHER_API_KEY)
Inspecting with the MCP Inspector
BASE=http://127.0.0.1:9001/mcp
# List capabilities (run tools/list first)
npx @modelcontextprotocol/inspector --cli $BASE --transport http --method tools/list
npx @modelcontextprotocol/inspector --cli $BASE --transport http --method resources/list
npx @modelcontextprotocol/inspector --cli $BASE --transport http --method prompts/list
# Call a tool
npx @modelcontextprotocol/inspector --cli $BASE --transport http \
--method tools/call --tool-name mytool --tool-arg key=value
# Multiple args, or JSON for complex parameters
npx @modelcontextprotocol/inspector --cli $BASE --transport http \
--method tools/call --tool-name mytool --tool-arg key1=v1 --tool-arg key2=v2
npx @modelcontextprotocol/inspector --cli $BASE --transport http \
--method tools/call --tool-name mytool --tool-arg 'options={"format":"json","max_tokens":100}'
# Custom headers (e.g. auth testing)
npx @modelcontextprotocol/inspector --cli $BASE --transport http \
--method tools/list --header "X-API-Key: your-api-key"
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.
- 2mo ago First seen · 75 lines · 58 tokens per session scan A cf39cd47493e
mcp-inspector-testing is a skill published in the GitHub repository microsoft/wassette (972 stars, last pushed 2d ago), licensed MIT. It adds 58 tokens to every session and 725 once invoked, about $0.0002 per session on Opus 5.5. 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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