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.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/instructions/microsoft/wassette/agents-md)<a href="https://agentmods.dev/instructions/microsoft/wassette/agents-md"><img src="https://agentmods.dev/badge/instructions/microsoft/wassette/agents-md/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/instructions/microsoft/wassette/agents-md"><img src="https://agentmods.dev/badge/instructions/microsoft/wassette/agents-md.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00476 | $0.00476 |
| Opus 5.5 | $0.00190 | $0.00190 |
| Sonnet 5.5 | $0.00095 | $0.00095 |
| Haiku 4.5 | $0.00048 | $0.00048 |
Grade A, and why
wassette AGENTS.md 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 — 50 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Agent Guide for Wassette
Wassette is an MCP server that runs tools as WebAssembly components with Wasmtime. This file is the entry point for coding agents and contributors; the linked documentation and skills are the canonical sources for detailed guidance.
Start here
- Contributing: contribution requirements and release-note policy.
- Developer guide: prerequisites, repository layout, build, test, lint, documentation, and local CI workflows.
- Architecture: system design and component boundaries.
- Release process: release automation and versioning.
Agent skills
Focused workflows live under .agents/skills/:
| Skill | Use it for |
|---|---|
build-and-test |
Building the workspace, examples, and test components |
rust-code-style |
Rust design, formatting, Clippy, and dependency checks |
copyright-headers |
Applying the required headers to Rust files |
mcp-inspector-testing |
Testing server behavior through MCP Inspector |
documentation |
Writing, building, and previewing the mdBook |
pull-request |
Writing concise, user-facing pull requests |
Agents that support the Agent Skills standard should invoke the relevant skill.
Other agents should read its SKILL.md before performing that workflow.
Repository requirements
- Prefer the repository
justrecipes over ad-hoc commands; several recipes build required WebAssembly components before the Rust workspace. - Format Rust with
cargo +nightly fmt, lint withcargo clippy --workspace, and check unused dependencies withcargo machete. - Every Rust source file must begin with the Microsoft copyright header; use
./scripts/copyright.sh. - Validate server-facing behavior with MCP Inspector when the change affects MCP tools, resources, prompts, transports, or runtime behavior.
- Release notes are generated from pull request titles. Write a clear,
user-facing title; do not create or update a
CHANGELOG.md.
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 · 50 lines · 476 tokens per session scan A b3059fb6d6fc
wassette AGENTS.md is an instructions file published in the GitHub repository microsoft/wassette (972 stars, last pushed 2d ago), licensed MIT. It adds 476 tokens to every session, about $0.0019 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.
Other instructions, from other repositories
vscode buildNext.instructions.md
Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).
next.js AGENTS.md
AGENTS.md instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.
vscode oss-third-party-notices.instructions.md
Instructions for microsoft/vscode, covering vs code oss third-party-notices pipeline, architecture, pipeline flow in ci, cache eligibility and rollout and applying the notice (cutover).
langchain AGENTS.md
AGENTS.md instructions for langchain-ai/langchain, covering global development guidelines for the langchain monorepo, corridor security analysis, project architecture and context, monorepo structure and development tools & commands.
vscode copilot-instructions.md
Copilot instructions for microsoft/vscode, covering vs code copilot instructions, project overview, root folders, core architecture (src/ folder) and built-in extensions (extensions/ folder).
deepseek-harness AGENTS.md
AGENTS.md instructions for deepseek-ai/deepseek-harness, covering agents.md, pre-stable apis and released session data, repository layout, commands and host sandbox failures.