Borrowing it
Nothing to install: this file belongs to vantage-sh/vantage-mcp-server. 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/vantage-sh/vantage-mcp-server/main/.agents/skills/writing-mcp-tools/SKILL.mdgit clone --depth 1 https://github.com/vantage-sh/vantage-mcp-serverWrote 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/vantage-sh/vantage-mcp-server/writing-mcp-tools)<a href="https://agentmods.dev/skills/vantage-sh/vantage-mcp-server/writing-mcp-tools"><img src="https://agentmods.dev/badge/skills/vantage-sh/vantage-mcp-server/writing-mcp-tools/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/vantage-sh/vantage-mcp-server/writing-mcp-tools"><img src="https://agentmods.dev/badge/skills/vantage-sh/vantage-mcp-server/writing-mcp-tools.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 3 findings, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium Agent Snooping · line 134 Skill enumerates or reads other installed skills. Access to other skills' SKILL.md files or the skills directory reveals prompt instructions, capabilities, and secrets that should be invisible to peer skills.Fix: Remove all code or instructions that list or read other skills' files or directories. Skills should operate independently; cross-skill access is a privilege escalation.
- medium Agent Snooping · line 271 Skill enumerates or reads other installed skills. Access to other skills' SKILL.md files or the skills directory reveals prompt instructions, capabilities, and secrets that should be invisible to peer skills.Fix: Remove all code or instructions that list or read other skills' files or directories. Skills should operate independently; cross-skill access is a privilege escalation.
- medium Agent Snooping · line 285 Skill enumerates or reads other installed skills. Access to other skills' SKILL.md files or the skills directory reveals prompt instructions, capabilities, and secrets that should be invisible to peer skills.Fix: Remove all code or instructions that list or read other skills' files or directories. Skills should operate independently; cross-skill access is a privilege escalation.
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 | $0.00070 | $0.03857 |
| Opus 5 | $0.00035 | $0.01929 |
| Sonnet 5 | $0.00014 | $0.00771 |
| Haiku 4.5 | $0.00007 | $0.00386 |
Grade A, and why
writing-mcp-tools 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 12d 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 — 287 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Writing MCP tools
Every tool in this repo is a thin wrapper around a Vantage REST endpoint, registered through registerTool and tested with testTool. The recipe below is what a new tool should look like. Read it before adding files under src/tools/.
Where the file goes
New tools are nested under a resource directory. Pick (or create) a directory named after the resource family — e.g. src/tools/budgets/, src/tools/recommendation-views/. Inside that directory:
src/tools/<resource>/
index.ts # one `import "./<verb>-<resource>"` line per tool
<verb>-<resource>.ts # tool file (list, get, create, update, delete, …)
schemas.ts # shared zod objects when multiple tools in the folder reuse them
test/tools/<resource>/
<verb>-<resource>.test.ts # unit tests — mirrors the src layout under test/
Create src/tools/<resource>/index.ts with one import "./<verb>-<resource>" line per tool, then run npm run generate-tools-index. That regenerates src/tools/index.ts to include the new directory — do not edit src/tools/index.ts by hand.
Do not add tool files at the top level of src/tools/. Every tool belongs under its resource directory.
Shared schemas (schemas.ts)
Nesting tools under one resource folder exists so siblings can share zod without copy-paste. When two or more tools in src/tools/<resource>/ use the same argument shapes (or the same shape with create defaults vs update optionals), extract them into schemas.ts in that folder — do not duplicate constants or z.object(...) blocks across create-* and update-* files.
Reference: src/tools/budgets/schemas.ts (budgetPeriod for create-budget and update-budget). Cost reports: src/tools/cost-reports/schemas.ts (chartTypes, chartSettings, businessMetricTokenForCreate / businessMetricTokenForUpdate, costReportSettingsForCreate / costReportSettingsForUpdate, dateBins).
Rules:
- Import shared exports from
./schemasin each tool file; keep tool-specific fields (tokens, titles, one-off describes) in the tool file. - If create and update differ only by
.default(...)vs.optional(), export two named schemas (e.g.costReportSettingsForCreateandcostReportSettingsForUpdate) rather than maintaining two nearly identical inline copies. - Add or extend
schemas.tsin the same PR as a new create/update pair when you introduce the second file that would duplicate an existing definition. schemas.tsis not imported fromindex.ts— only tool files import it. It is not registered as a tool.
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.
- 12d ago First seen · 287 lines · 70 tokens per session scan A ef54fbd797e5
writing-mcp-tools is a skill published in the GitHub repository vantage-sh/vantage-mcp-server (84 stars, last pushed today), licensed MIT. It adds 70 tokens to every session and 3,857 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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