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.
npx skills add PracticalSwan/agent-skills --skill mcp-buildergit clone --depth 1 https://github.com/PracticalSwan/agent-skillsWrote 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/practicalswan/agent-skills/mcp-builder)<a href="https://agentmods.dev/skills/practicalswan/agent-skills/mcp-builder"><img src="https://agentmods.dev/badge/skills/practicalswan/agent-skills/mcp-builder/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/practicalswan/agent-skills/mcp-builder"><img src="https://agentmods.dev/badge/skills/practicalswan/agent-skills/mcp-builder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to high
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 →
- high Prompt Injection · line 205 Hidden instructions were detected in comments or invisible text. These could contain malicious directives. Manual review is recommended.Fix: Audit all comments and invisible characters. Remove any instructions that direct the agent to perform unauthorized actions. Use plain, reviewable content.
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 | $0.00047 | $0.01836 |
| Opus 5 | $0.00023 | $0.00918 |
| Sonnet 5 | $0.00009 | $0.00367 |
| Haiku 4.5 | $0.00005 | $0.00184 |
Grade A, and why
mcp-builder 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 3d 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 — 236 lines — stays where its author put it; the contents beside it link to each section on GitHub.
MCP Builder
Design MCP servers that are easy for agents to discover, compose, and trust.
- Leverage native parallel subagent dispatch and 200k+ context windows where available.
When to Use
Use symptom -> action triggers: when one matches, apply this skill and verify with the protocol below.
- You are creating a new MCP server around an external API or internal platform.
- An existing MCP server needs better tool naming, schemas, pagination, or error handling.
- You need a workflow for evaluating whether an MCP server is actually useful for real agent tasks.
- You are deciding between TypeScript and Python MCP implementations.
Glossary
- MCP Inspector: An interactive client for browsing registered tools, schemas, inputs, and outputs while you validate a server.
- Structured outputs: Predictable JSON or schema-backed payloads that downstream agents can parse safely instead of scraping prose.
- Workflow tool: A higher-level tool that coordinates several lower-level API steps into one agent-friendly operation.
Core Workflow
1. Research First
Before implementation:
- Read the current MCP protocol documentation.
- Read the relevant SDK guide for your implementation language.
- Review the target service API and list the highest-value operations.
- Decide which operations should stay low-level and which deserve dedicated workflow tools.
2. Design Agent-Friendly Tools
Prefer tools that are easy to discover and compose:
- use clear action-oriented names
- keep schemas explicit and constrained
- support pagination and filters where lists can grow
- return structured content whenever the client can benefit from it
- write error messages that tell the agent what to do next
3. Implement Shared Infrastructure
Build common pieces before individual tools:
- authenticated API client
- error formatter
- response normalizer
- pagination helpers
- reusable schema utilities
4. Test the Server Like an Agent Would
Verify more than syntax:
What ships with it
10 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
- CHANGELOG.md 6.4 KB
- LICENSE.txt 11 KB
- reference/evaluation.md 21 KB
- reference/mcp_best_practices.md 7.2 KB
- reference/node_mcp_server.md 28 KB
- reference/python_mcp_server.md 25 KB
- scripts/connections.py 4.8 KB runs code
- scripts/evaluation.py 12 KB runs code
- scripts/example_evaluation.xml 1.2 KB
- scripts/requirements.txt 29 B
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.
- 3d ago Changed 313a330fe648
- 4d ago Changed be71c2348c64
- 7d ago First seen · 236 lines · 47 tokens per session scan A 962c9f24e9a3
mcp-builder is a skill published in the GitHub repository PracticalSwan/agent-skills (14 stars, last pushed 3d ago), licensed MIT. It adds 47 tokens to every session and 1,836 once invoked, about $0.0002 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 2026-09-03.
Other skills, from other repositories
code-review
Reviews diffs by severity to produce actionable feedback.
refactoring
Safe, test-backed code restructuring in small steps.
requesting-code-review
Self-reviews work against the plan before sign-off.
test-writing
Writes meaningful tests that actually catch bugs.
workflow-builder
Use when building and automating business workflows with Notion task tracking, Slack notifications, Kanban boards, and cross-functional process orchestration.
flowise-builder
Use when flowise visual LLM workflow builder — drag-drop chatflows, API endpoints, document loaders, tools. Use when working with flowise builder.