add-tool

add-tool is a skill for Claude Code from cyanheads/pentest-mcp-server. It costs 35 tokens per session (17,726 once invoked), scanned A, a copy of add-tool, Apache-2.0.

A scaffold for adding a new MCP tool to an existing server. MCP is a standard way for an AI client to call tools provided by another program.

In plain words
What is it for?
Use it when implementing a new server capability, including tools that may need user input or confirmation.
Why use it?
It removes the repetitive setup of creating the tool file, registering it, and checking that the server still works.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: mentions Claude Code.

Part of the pentest-mcp-server plugin — 33 skills, 1 MCP server shipped together

Good fit Use it when implementing a new server capability, including tools that may need user input or confirmation.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/cyanheads/pentest-mcp-server/add-tool
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add cyanheads/pentest-mcp-server --skill add-tool
Clone the repo
git clone --depth 1 https://github.com/cyanheads/pentest-mcp-server

Made for: Claude Code.

Or install pentest-mcp-server, the plugin that ships this one along with the rest of its 33 skills, 1 MCP server.

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.

agentmods badge for add-tool

README.md
[![agentmods](https://agentmods.dev/badge/skills/cyanheads/pentest-mcp-server/add-tool/github.svg)](https://agentmods.dev/skills/cyanheads/pentest-mcp-server/add-tool)
Your own site
<a href="https://agentmods.dev/skills/cyanheads/pentest-mcp-server/add-tool"><img src="https://agentmods.dev/badge/skills/cyanheads/pentest-mcp-server/add-tool/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.

agentmods 80×15 button for add-tool

Your own site · 80×15
<a href="https://agentmods.dev/skills/cyanheads/pentest-mcp-server/add-tool"><img src="https://agentmods.dev/badge/skills/cyanheads/pentest-mcp-server/add-tool.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 35 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 17,726 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe.
Origin 100% copy Near-identical to another mod 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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00035 $0.17726
Opus 5.5 $0.00014 $0.07090
Sonnet 5.5 $0.00007 $0.03545
Haiku 4.5 $0.00003 $0.01773

Measured 15d ago against content hash 9210f47a1f51, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

add-tool scanned grade A with 1 finding 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 15d 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

const articles = await fetch(input.pmids);
Origin

This is a copy

100% identical to add-tool — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

framework-skills/add-tool/SKILL.md · 903 lines

How it starts

The opening of the file, as written. The whole thing — 903 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Context

Tools use the tool() builder from @cyanheads/mcp-ts-core. Each tool lives in src/mcp-server/tools/definitions/ with a .tool.ts suffix. The standard registration pattern uses a definitions/index.ts barrel that collects all tools into an allToolDefinitions array for createApp(). Fresh scaffolds from init start with direct imports in src/index.ts — the barrel is introduced as definitions grow. Match the pattern already used by the project you're editing.

Steps

  1. Gather the tool's name, purpose, and input/output shape from the user's request — ask only if genuinely absent
  2. Determine if it needs input the caller may not supply — a confirmation, a choice, the client's roots — which makes it a multi-round-trip handler (ctx.requestInput / ctx.inputs, see api-context)
  3. Create the file at src/mcp-server/tools/definitions/{{tool-name}}.tool.ts
  4. Register the tool in the project's existing createApp() tool list (directly in src/index.ts for fresh scaffolds, or via a barrel if the repo already has one)
  5. Run bun run devcheck to verify — it applies Biome's formatting fixes as it runs
  6. Smoke-test with bun run rebuild && bun run start:stdio < /dev/null (or start:http) — the Core services constructed log record must list the new tool in its tools field (the message text shows only counts); if it doesn't, the tool never reached createApp()

Naming

Tools use lowercase snake_case with a canonical server/domain prefix, {server}_{verb}_{noun} by default. Drop the noun only when the verb is a complete action on its own (git_pull, git_status): if {server}_{verb} leaves "…what?" unanswered — search what? connect to what? — the noun is missing. The full rule is the Name row of the design-mcp-server Design table.

Examples: pubmed_search_articles, pubmed_fetch_fulltext, clinicaltrials_find_eligible.

The server prefix is judged on clarity, not length: the brand name or the plain well-known word for the domain both pass (pubmed_, patents_); an abbreviation fails only when it reads as something else out of context (loc_, ct_). A fourth segment is fine when the noun is inherently two words (openfda_search_device_clearances). When a name resists the schema — can't pick a verb, noun feels generic, the verb wants a second word — that's usually a signal the scope is fuzzy; split the tool, rename, or reconsider.

Read the full file on GitHub · 903 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.

  1. 15d ago Changed · +21 lines 9210f47a1f51
  2. 1mo ago Changed · +78 lines 95ce1591e082
  3. 1mo ago First seen · 804 lines · 35 tokens per session scan A 5ba100b246b6

Subscribe to this mod's changes

add-tool is a skill published in the GitHub repository cyanheads/pentest-mcp-server (1 stars, last pushed 7d ago), licensed Apache-2.0. It adds 35 tokens to every session and 17,726 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 1 finding (makes network calls). It is 100% identical to add-tool, differing in 0 lines, and is treated as a copy.

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