Borrowing it
Nothing to install: this file belongs to radimsem/mithril. 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/radimsem/mithril/main/.claude/skills/tool-creator/SKILL.mdgit clone --depth 1 https://github.com/radimsem/mithrilWrote 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/radimsem/mithril/tool-creator)<a href="https://agentmods.dev/skills/radimsem/mithril/tool-creator"><img src="https://agentmods.dev/badge/skills/radimsem/mithril/tool-creator/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/radimsem/mithril/tool-creator"><img src="https://agentmods.dev/badge/skills/radimsem/mithril/tool-creator.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 | $0.00039 | $0.05760 |
| Opus 5.5 | $0.00016 | $0.02304 |
| Sonnet 5.5 | $0.00008 | $0.01152 |
| Haiku 4.5 | $0.00004 | $0.00576 |
Grade A, and why
tool-creator 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.
How it starts
The opening of the file, as written. The whole thing — 552 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Tool Creator
Implementation guide for Mithril MCP server execution tools.
Overview
Each tool wraps a single command (POSIX, git, etc.) as a structured MCP tool. Tools are never shell strings - they build typed argument vectors validated before execution.
File Placement
Tool lives in crates/tools/src/<category>/<tool_name>.rs where category groups related commands:
| Category | Examples |
|---|---|
system/ |
Ls, Cp, Rm, Grep, Find, Sed, Awk |
git/ |
GitStatus, GitCommit, GitLog, GitDiff |
PascalCase tool name, snake_case file name: GitStatus -> git/git_status.rs.
Register in crates/tools/src/<category>/mod.rs with pub mod <tool_name>;.
Pre-Implementation Verification
Before writing any code, verify the tool's CLI interface and sandbox compatibility. This section applies only to tools that wrap a CLI command — skip it for general-purpose tools like RunChain that implement execution logic rather than wrapping a binary.
1. CLI interface check
Run <cmd> --help (or <cmd> <subcommand> --help) to get the up-to-date flag reference. Use this output — not memory or documentation — to decide which arguments to expose in the Args struct.
# Examples
grep --help
git diff --help
cargo clippy --help
Cross-check the flag names, short forms, and value types against the help output before writing the parameters() JSON schema. Mismatches between the schema and the real CLI are the most common source of CmdError in tests.
2. Version check
Run <cmd> --version to confirm the developer has a recent version installed:
go version # → go1.22.0 or newer
cargo --version # → cargo 1.78.0 or newer
If the installed version is notably old (e.g. Go < 1.21, Cargo < 1.70), inform the developer to upgrade for reliable testing. If the command is not found at all, the tool should declare available() returning false (see ToolDef section below).
Trust --help over documentation or memory. Real CLI interfaces diverge from docs frequently. Common divergences found in this project:
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 · 552 lines · 39 tokens per session scan A 40642bff9214
tool-creator is a skill published in the GitHub repository radimsem/mithril (15 stars, last pushed 6mo ago), licensed Apache-2.0. It adds 39 tokens to every session and 5,760 once invoked, about $0.0002 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.
Other skills, from other repositories
mcp-builder
Design, build, configure, or debug Model Context Protocol servers for codewhale, including stdio and HTTP/SSE transports.
nextjs-fullstack
Use for Next.js App Router, React Server Components, server actions, API routes, auth, database integration, caching, deployment, or full-stack product features.
notion
Notion API for creating and managing pages, databases, and blocks.
pstack-principle-boundary-discipline
Apply when wiring validation, error handling, or framework adapters. Concentrate guards at system boundaries (CLI, config, network, external APIs); trust internal types and keep business logic in pure functions.
pstack-principle-make-operations-idempotent
Apply when designing commands, lifecycle steps, or processing loops that run amid crashes, restarts, and retries. Converge to the same end state regardless of partial prior runs.
pstack-make-bot-ui
Use when building a custom UI (page, dashboard, buttons) that should wake a Grok Bot over a webhook, when the user must provide a webhook sender key, or when exposing that UI on Tailscale.