What is cordyceps CLAUDE.md?

A project guide for Cordyceps, a .NET 8 Grasshopper plugin that lets AI assistants control Grasshopper and Rhino through the Model Context Protocol. It describes the main server, component, build command, and architecture.

Use it to understand the MCP server and Grasshopper component, locate functionality, and build the plugin with the documented .NET command so the .gha output is produced.

It gives coding agents the repository’s expected structure and build rules, including the requirement to build the release configuration. This reduces mistakes when modifying or compiling the plugin.

How brookstalley/cordyceps configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to brookstalley/cordyceps. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/brookstalley/cordyceps/develop/CLAUDE.md

Clone the repo

git clone --depth 1 https://github.com/brookstalley/cordyceps

Made for: Claude Code.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/brookstalley/cordyceps/claude-md/github.svg)](https://agentmods.dev/instructions/brookstalley/cordyceps/claude-md)

Your own site

<a href="https://agentmods.dev/instructions/brookstalley/cordyceps/claude-md"><img src="https://agentmods.dev/badge/instructions/brookstalley/cordyceps/claude-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.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/brookstalley/cordyceps/claude-md"><img src="https://agentmods.dev/badge/instructions/brookstalley/cordyceps/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 2,892 This file is loaded in full into every session.

When invoked 2,892 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

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	$0.02892	$0.02892
Opus 5.5	$0.01157	$0.01157
Sonnet 5.5	$0.00578	$0.00578
Haiku 4.5	$0.00289	$0.00289

Measured 2mo ago against content hash c7b692ce360f, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

cordyceps CLAUDE.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.

CLAUDE.md · 210 lines

How it starts

The opening of the file, as written. The whole thing — 210 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Project Overview

Cordyceps is a Grasshopper plugin that exposes Grasshopper and Rhino functionality via the Model Context Protocol (MCP). It allows AI assistants to programmatically control Grasshopper (adding components, creating connections, configuring scripts) and Rhino (managing objects, layers, materials, rendering).

Build Commands

# Build the plugin (Release configuration required)
dotnet build src/Cordyceps/Cordyceps.csproj -c Release

# The built .gha file is automatically copied to releases/ (gitignored - a build output)

The project targets .NET 8.0 and outputs a Grasshopper plugin (.gha file). Debug builds are blocked—always use -c Release.

Architecture

Core Components

McpServer.cs - HTTP/SSE server implementing the MCP protocol. Listens on a configurable port (default 26929), handles JSON-RPC requests, and manages SSE sessions for streaming responses. Discovers tools via reflection using [McpServerToolType] and [McpServerTool] attributes.

CordycepsComponent.cs - The Grasshopper component that users drop on the canvas. Manages the MCP server lifecycle - starts the server when placed, stops when removed. Outputs server status and last command received.

Core/GrasshopperContext.cs - Thread-safe wrapper for Grasshopper document access. All Grasshopper operations must run on the UI thread; this class provides ExecuteOnUiThread() methods that marshal calls correctly.

Core/ComponentRegistry.cs - Resolves component type names to actual Grasshopper components. Handles aliases (e.g., "python" -> "Python 3 Script") and supports creation by name or GUID.

Core/UnifiedToolHelpers.cs - Shared utilities for the unified tool architecture including action dispatch, help generation, and standardized response formatting.

Core/ToolHelpers.cs - Shared document/component utilities used across every tool: active-document and component resolution (by GUID or name), protected/infrastructure-id checks, cluster-safe recompute, component-info builders, JSON (de)serialization helpers, and SuccessResponse/ErrorResponse formatting.

Read the full file on GitHub · 210 lines

Changes

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 · 210 lines · 2,892 tokens per session scan A c7b692ce360f

Subscribe to this mod's changes

cordyceps CLAUDE.md is an instructions file published in the GitHub repository brookstalley/cordyceps (108 stars, last pushed 2mo ago), licensed MIT. It adds 2,892 tokens to every session, about $0.0116 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.

Building agents grasshopper mcp rhino3d

cordyceps CLAUDE.md next to 6 instructions from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
cordyceps CLAUDE.mdbrookstalley/cordyceps	Instructions file	108	2mo ago	MIT	A	2,892	Claude Code
vscode buildNext.instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	9,719	GitHub Copilot
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vscode oss-third-party-notices.instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	5,516	GitHub Copilot
vscode copilot-instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	3,093	GitHub Copilot
deepseek-harness AGENTS.mddeepseek-ai/deepseek-harness	Instructions file	274k	2d ago	MIT	A	4,313	Codex, OpenCode

cordyceps: Instructions file for Claude Code