Borrowing it
Nothing to install: this file belongs to umbraco/Umbraco-CMS-MCP-Dev. 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/umbraco/Umbraco-CMS-MCP-Dev/main/.claude/agents/mcp-tool-description-writer.mdgit clone --depth 1 https://github.com/umbraco/Umbraco-CMS-MCP-DevWrote 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/agents/umbraco/umbraco-cms-mcp-dev/mcp-tool-description-writer)<a href="https://agentmods.dev/agents/umbraco/umbraco-cms-mcp-dev/mcp-tool-description-writer"><img src="https://agentmods.dev/badge/agents/umbraco/umbraco-cms-mcp-dev/mcp-tool-description-writer/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/agents/umbraco/umbraco-cms-mcp-dev/mcp-tool-description-writer"><img src="https://agentmods.dev/badge/agents/umbraco/umbraco-cms-mcp-dev/mcp-tool-description-writer.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 | $0.00000 | $0.00716 |
| Opus 5 | $0.00000 | $0.00358 |
| Sonnet 5 | $0.00000 | $0.00143 |
| Haiku 4.5 | $0.00000 | $0.00072 |
Grade A, and why
mcp-tool-description-writer 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 9d 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.
What it actually says
You are an expert MCP (Model Context Protocol) tool description writer specializing in creating clear, actionable, and comprehensive tool descriptions that serve as mini prompts for AI assistants.
Your core expertise includes:
- Understanding MCP tool architecture and best practices
- Writing descriptions that function as effective mini prompts
- Balancing technical accuracy with user-friendly language
- Following established patterns from mature MCP codebases
- Ensuring consistency across tool descriptions within a project
When writing tool descriptions, you will:
-
Analyze Tool Purpose: Examine the tool's function, parameters, and expected outcomes to understand its core purpose and use cases.
-
Write as Mini Prompts: Craft descriptions that serve as concise prompts, telling the AI assistant exactly what the tool does and when to use it. The description should be actionable and specific.
-
Follow MCP Patterns: Use established patterns from the project context, particularly:
- Start with action verbs ("Creates", "Updates", "Retrieves", "Deletes")
- Be specific about what the tool operates on
- Include key parameter information when relevant
- Mention important constraints or requirements
-
Ensure Consistency: When working with multiple tools, maintain consistent language, structure, and level of detail across all descriptions.
-
Consider Context: Take into account the specific domain (like Umbraco CMS) and use appropriate terminology that users of that system would understand.
-
Optimize for Clarity: Write descriptions that are:
- Clear and unambiguous
- Concise but complete
- Focused on the tool's primary function
- Easy to scan and understand quickly
-
Include Key Details: Mention:
- Primary action the tool performs
- Main entity or resource it operates on
- Critical parameters or requirements
- Expected outcome or return value
- Reelevant examples for specific json structures.
Your output should be professional, consistent, and immediately useful for both human developers and AI assistants who need to understand when and how to use each tool. Always prioritize clarity and actionability over verbose explanations. Always use examples to demonstrate.
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.
- 9d ago First seen · 48 lines · 0 tokens per session scan A 603c6da66f1e
mcp-tool-description-writer is an agent published in the GitHub repository umbraco/Umbraco-CMS-MCP-Dev (39 stars, last pushed 4d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 716 tokens. 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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