Borrowing it
Nothing to install: this file belongs to adawalli/nexus. 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/adawalli/nexus/main/.claude/skills/mcp-tool-skill/SKILL.mdgit clone --depth 1 https://github.com/adawalli/nexusWrote 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/adawalli/nexus/mcp-tool-skill)<a href="https://agentmods.dev/skills/adawalli/nexus/mcp-tool-skill"><img src="https://agentmods.dev/badge/skills/adawalli/nexus/mcp-tool-skill/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/adawalli/nexus/mcp-tool-skill"><img src="https://agentmods.dev/badge/skills/adawalli/nexus/mcp-tool-skill.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00056 | $0.00994 |
| Opus 5 | $0.00028 | $0.00497 |
| Sonnet 5 | $0.00011 | $0.00199 |
| Haiku 4.5 | $0.00006 | $0.00099 |
Grade A, and why
mcp-server-instructions 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.
How it starts
The opening of the file, as written. The whole thing — 111 lines — stays where its author put it; the contents beside it link to each section on GitHub.
MCP Server Instructions
Write workflow-focused server instructions that help LLMs understand your server's capabilities.
What Instructions Are
The instructions field is an optional string in MCP's InitializeResult that gets injected into the LLM's system prompt. It helps models understand:
- How to use your server's tools together
- When to search for specific tools (with tool compaction)
- Operational constraints and patterns
Evidence: In controlled testing, well-written instructions improved task success from 60% to 85% - a 25% improvement.
Template
instructions="""[Server name] for [domain] operations.
KEY WORKFLOWS:
- [Name]: [tool1] -> [tool2] -> [tool3]
- [Name]: [tool1] -> [tool2] (when [condition])
CONSTRAINTS:
- [Limit or behavior users need to know]
- [Input format quirks]
- [Auto-pagination or chunking behavior]"""
What to Include
Focus on what individual tool descriptions don't convey:
| Include | Example |
|---|---|
| Cross-tool relationships | "Always call authenticate before any fetch_* tools" |
| Operational patterns | "Search results expire after 10 minutes" |
| Constraints | "Rate limited to 100 requests/minute" |
| Sequencing | "Use get_metadata before fetching large content" |
| Format flexibility | "IID accepts: #72, !72, '72', 72" |
What to Avoid
| Avoid | Why | Instead |
|---|---|---|
| Repeating tool descriptions | Already in tool docstrings | Show how tools work together |
| Marketing language | "comprehensive", "powerful" add no value | State capabilities factually |
| Lengthy manuals | Instructions should be <500 chars | Be concise and actionable |
| Listing all tools | Tools are discoverable | Only mention in workflow context |
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 · 111 lines · 56 tokens per session scan A 9e8d71f92c26
mcp-server-instructions is a skill published in the GitHub repository adawalli/nexus (23 stars, last pushed 28d ago), licensed MIT. It adds 56 tokens to every session and 994 once invoked, about $0.0003 per session on Opus 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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