writing-mcp-toolsets

writing-mcp-toolsets is a skill for Claude Code, Codex from developmentseed/mcp-toolsets-runtime. It costs 72 tokens per session (1,959 once invoked), scanned A, original, MIT.

A guide for building Python tool packages that run through the MCP server runtime. It explains the required tool format, stored session values, user credentials, and interface views.

In plain words
What is it for?
Use it when adding a new tool package, converting a Python library or script into tools, or investigating why a tool package will not start.
Why use it?
It helps avoid packages that the runtime cannot load or serve, and prevents incompatible local changes to shared runtime code.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it when adding a new tool package, converting a Python library or script into tools, or investigating why a tool package will not start.

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Install with agentmods
npx agentmods add skills/developmentseed/mcp-toolsets-runtime/skill
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 developmentseed/mcp-toolsets-runtime --skill skill
Clone the repo
git clone --depth 1 https://github.com/developmentseed/mcp-toolsets-runtime

Made for: Claude Code, Codex.

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 writing-mcp-toolsets

README.md
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Your own site
<a href="https://agentmods.dev/skills/developmentseed/mcp-toolsets-runtime/skill"><img src="https://agentmods.dev/badge/skills/developmentseed/mcp-toolsets-runtime/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.

agentmods 80×15 button for writing-mcp-toolsets

Your own site · 80×15
<a href="https://agentmods.dev/skills/developmentseed/mcp-toolsets-runtime/skill"><img src="https://agentmods.dev/badge/skills/developmentseed/mcp-toolsets-runtime/skill.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 72 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,959 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 original No closer match found 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 $0.00072 $0.01959
Opus 5.5 $0.00029 $0.00784
Sonnet 5 $0.00014 $0.00392
Haiku 4.5 $0.00007 $0.00196

Measured 7d ago against content hash e877e7ba1b35, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-25, from the pricing page.

Security

Grade A, and why

writing-mcp-toolsets 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 7d 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.

| `requests`, `urllib` | `httpx.AsyncClient` |
src/mcp_toolset/skill/SKILL.md · 195 lines

How it starts

The opening of the file, as written. The whole thing — 195 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Writing a toolset

A toolset is a Python package that exports a list of LangChain tools. The runtime imports it by name and serves it over MCP.

This file is the procedure. The detail lives in the mcp-toolsets-runtime documentation: CONSUMING for the contract, SESSION-STATE for stored values. A marker like (#4c) below means that section of CONSUMING. Read those for detail; this file does not reproduce them.

Get these right first

They are cheap now and expensive later.

1. The consuming repo owns no runtime code. mcp_runtime, mcp_state, mcp_cli, mcp_agent, mcp_agent_api and mcp_toolset come from the mcp-toolsets-runtime package. Never add a module under one of those names, and never patch runtime behaviour locally. If the runtime is wrong, fix it in the runtime, release it, and bump the pin.

2. Data key names are public. Every key in a tool's return except message is stored as <toolset>/<tool>/<field>. The agent's model reads that name when it decides which stored value to pass into a later call, and that call may land in a different toolset. The key is the only thing the two share: no types, no imports, no registry.

So name the thing, not its type. area_of_interest is a good key; geometry is a bad one, because a coverage footprint is also a geometry and the two are identical JSON. A model handed the wrong one produces confident nonsense and nothing will notice. (#4c)

3. Scaffold, never hand-roll. mcp-toolset new writes the package, the test, the pyproject and whatever deployment config the repo declares. A hand-made directory misses files you will not notice until deploy.

Steps

1. Scaffold

uv run mcp-toolset new my-toolset          # --with-ui to add a React view

This writes toolsets/my-toolset/ containing src/my_toolset/tools.py, a test, a pyproject, and the deployment file the repo's root pyproject declares under [tool.mcp-toolset] deployment-config.

2. Write the tools

tools.py must export TOOLS, a non-empty list. Two exports are optional: VIEWS maps a tool name to a view id, and CREDENTIAL_HEADERS lists the HTTP headers the tools read. (#2)

Read the full file on GitHub · 195 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. 7d ago First seen · 195 lines · 72 tokens per session scan A e877e7ba1b35

Subscribe to this mod's changes

writing-mcp-toolsets is a skill published in the GitHub repository developmentseed/mcp-toolsets-runtime (0 stars, last pushed yesterday), licensed MIT. It adds 72 tokens to every session and 1,959 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-18.

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