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Wassette MCP Server

Microsoft-maintained MCP server and security-oriented WebAssembly component runtime for loading sandboxed tools, managing component permissions, and exposing Wasm component tools to Claude through MCP.

by Microsoft·added 2026-06-06·
Claude CodeClaude Desktop
HarnessClaude CodeClaude Desktop
Review first — review before installing

Open the source and read safety notes before installing.

Safety notes

  • Wassette can load WebAssembly components from local paths or OCI registries and expose their tools to Claude.
  • Built-in MCP tools can load and unload components, search the component registry, list loaded components, and grant or revoke storage, network, and environment-variable permissions.
  • Components are sandboxed and deny access by default, but granted permissions can still allow file reads, file writes, outbound network calls, and secret access.
  • Review component source, registry provenance, policy files, requested permissions, and update channels before loading a component in a trusted workspace.
  • Require human approval before granting write access, broad filesystem scopes, production network hosts, or sensitive environment variables.

Privacy notes

  • Loaded components may process prompts, files, environment variables, network responses, secrets, and generated tool outputs depending on granted permissions.
  • Component directories, secrets directories, policy files, MCP transcripts, logs, registry URIs, and tool-call arguments can reveal sensitive project or credential details.
  • Wassette source includes argument log sanitization for keys, tokens, secrets, and passwords, but prompts and outputs can still contain private data.
  • Redact component ids, registry locations, local component names, granted URI scopes, environment keys, and tool outputs before sharing debug traces.

Prerequisites

  • Reviewed Wassette release or package-manager installation for the target platform.
  • MCP client that supports local stdio servers.
  • Agreement on which WebAssembly components may be loaded from local files or OCI registries.
  • Permission policy for storage, network, and environment-variable access before components are granted capabilities.
  • Separate secrets and component storage locations with appropriate filesystem permissions.

Schema details

Install type
cli
Troubleshooting
No
Source repository stats
Scope
Source repo
Collection metadata
Estimated setup
15 minutes
Difficulty
intermediate
Tool listing metadata
Disclosure
MIT-licensed Microsoft open-source project. Upstream documentation warns that Wassette is in early development and not production ready, so verify release maturity and permission behavior before deploying it broadly.
Full copyable content
{
  "mcpServers": {
    "wassette": {
      "command": "wassette",
      "args": ["run"]
    }
  }
}

About this resource

Content

Wassette MCP Server is Microsoft's security-oriented MCP runtime for loading WebAssembly components as tools. It runs as a local MCP server, exposes built-in component-management and permission-management tools, and lets Claude call tools provided by loaded Wasm components.

Use it when you want reusable WebAssembly component tools behind a sandboxed MCP runtime, with explicit storage, network, and environment-variable permissions instead of giving a component broad host access by default.

Source Review

These sources were reviewed on 2026-06-06. Prefer the live repository, MCP client guide, README, license, installation guide, built-in tools reference, permission reference, configuration reference, and MCP server source for current setup and behavior.

Features

  • Run Wassette as a local stdio MCP server with wassette run.
  • Load WebAssembly components from local files or OCI registry references.
  • List, unload, and inspect loaded components.
  • Search the known component registry for loadable tools.
  • Expose loaded component tools through the MCP tool list.
  • Grant and revoke storage permissions for specific file or directory scopes.
  • Grant and revoke outbound network access for specific hosts.
  • Grant and revoke environment-variable access for specific keys.
  • Keep components deny-by-default until permissions are explicitly granted.

Installation

Install Wassette with a reviewed release or package-manager workflow for the target platform. For example, the upstream docs include Homebrew installation on macOS and Linux:

brew tap microsoft/wassette https://github.com/microsoft/wassette
brew install wassette

Then register Wassette as a local stdio MCP server:

{
  "mcpServers": {
    "wassette": {
      "command": "wassette",
      "args": ["run"]
    }
  }
}

Review the upstream MCP client guide for client-specific setup, then load only components that have been reviewed for source, provenance, and permissions.

Use Cases

  • Load a reviewed WebAssembly component and expose its tools to Claude.
  • Give a component access only to the files, network hosts, or environment variables it needs.
  • Test reusable tool components without writing a dedicated MCP server for each tool.
  • Manage component permissions through MCP built-in tools during an agent session.
  • Use OCI-hosted components as portable tools across MCP clients.
  • Experiment with sandboxed component tooling while Wassette is still early in development.

Safety and Privacy

Wassette gives components a sandbox and deny-by-default permissions, but the MCP server also exposes tools that can grant capabilities. Treat every loaded component as code from a supply chain: review its source, registry path, policy, requested permissions, update channel, and expected outputs before granting access.

Be especially careful with storage write scopes, broad filesystem paths, production network hosts, and environment variables that contain credentials. MCP transcripts, component ids, registry URIs, policy files, secrets directories, logs, and tool outputs may reveal sensitive project details. Redact those values before sharing troubleshooting material.

Duplicate Check

No microsoft/wassette, Wassette MCP, WebAssembly component MCP, Wasm component tools, or matching source URL entry was found in content/mcp or README.md. Existing security, runtime, and tool-hosting MCP entries do not cover Wassette's Microsoft-maintained WebAssembly component runtime.

#webassembly#security#sandbox#tools#microsoft

Source citations

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