mcp-apps-builder

mcp-apps-builder is a skill for Claude Code, Codex from awslabs/cli-agent-orchestrator. It costs 137 tokens per session (1,721 once invoked), scanned A, original, Apache-2.0.

A guide for building MCP Apps, which are interactive user interfaces that can render inside a chat host through the Model Context Protocol.

In plain words
What is it for?
Use it to create a new MCP App, add a `ui://` view to an MCP server, migrate an OpenAI Apps SDK app, or make a web app work as an MCP App.
Why use it?
It provides the official process for creating these apps, adding them to existing MCP servers, or converting related web apps.

Skill for Claude CodeCodex

Written for Claude Code and Codex: Claude Code plugin machinery, but also reads ~/.codex or $CODEX_HOME. Also seen: reads .claude/ paths; mentions Claude Code; mentions Codex.

About the project

CLI Agent Orchestrator is a tool that coordinates multiple AI coding command-line programs by running them as separate workers in isolated terminal sessions. A supervisor uses it to delegate software tasks to specialist agents in parallel or in sequence while the workers retain their normal command-line capabilities. The catalogue skills operate this orchestration workflow.

awslabs/cli-agent-orchestrator · 1,213 stars · on GitHub · awslabs.github.io

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.

agentmods
npx agentmods add skills/awslabs/cli-agent-orchestrator/mcp-apps-builder
Any agent
npx skills add awslabs/cli-agent-orchestrator --skill mcp-apps-builder
Clone the repo
git clone --depth 1 https://github.com/awslabs/cli-agent-orchestrator

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 mcp-apps-builder

README.md
[![agentmods](https://agentmods.dev/badge/skills/awslabs/cli-agent-orchestrator/mcp-apps-builder.svg)](https://agentmods.dev/skills/awslabs/cli-agent-orchestrator/mcp-apps-builder)
Your own site
<a href="https://agentmods.dev/skills/awslabs/cli-agent-orchestrator/mcp-apps-builder"><img src="https://agentmods.dev/badge/skills/awslabs/cli-agent-orchestrator/mcp-apps-builder.svg" alt="Measured on agentmods" height="20"></a>
Per session 137 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,721 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00137 $0.01721
Opus 5 $0.00068 $0.00860
Sonnet 5 $0.00027 $0.00344
Haiku 4.5 $0.00014 $0.00172

Measured 6d ago against content hash 87f4d9c88033, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

mcp-apps-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 6d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/validate.sh), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

skills/mcp-apps-builder/SKILL.md · 114 lines

How it starts

The opening of the file, as written. The whole thing — 114 lines — stays where its author put it; the contents beside it link to each section on GitHub.

MCP Apps Builder (ext-apps Agent Skills bridge)

The Model Context Protocol ext-apps repo ships four official Agent Skills that teach an AI coding agent how to build MCP Apps (SEP-1865 — interactive ui:// UIs that render inside a chat host). This skill tells you when to reach for them and how to install them, so MCP App work is done with the canonical, up-to-date guidance instead of guesswork.

The four builder skills

Skill Use it when…
create-mcp-app Scaffolding a new MCP App (server + interactive UI) from scratch.
add-app-to-server Adding an interactive ui:// view to an existing MCP server's tools.
migrate-oai-app Converting an existing OpenAI Apps SDK app to MCP Apps.
convert-web-app Turning an existing web app into a hybrid web + MCP App.

Install / load them

Pick whichever matches the agent you're driving (skills live in the agent's skills directory — install once, then ask the agent to build):

  • Claude Code (plugin marketplace):
    /plugin marketplace add modelcontextprotocol/ext-apps
    /plugin install mcp-apps@modelcontextprotocol-ext-apps
    
  • Any agent (Vercel Skills CLI):
    npx skills add modelcontextprotocol/ext-apps
    
  • Manual (clone + copy into the agent's skills dir):
    git clone https://github.com/modelcontextprotocol/ext-apps.git
    cp -r ext-apps/plugins/mcp-apps/skills/create-mcp-app ~/.kiro/skills/create-mcp-app
    # …repeat for add-app-to-server / migrate-oai-app / convert-web-app
    
    Skills dirs by agent: Kiro CLI ~/.kiro/skills/, Claude Code ~/.claude/skills/, VS Code/Copilot ~/.copilot/skills/, Gemini CLI ~/.gemini/skills/, Codex ~/.codex/skills/, Cursor ~/.cursor/skills/, Goose ~/.config/goose/skills/. Verify with: ask the agent "what skills do you have?"

Read the full file on GitHub · 114 lines

Files

What ships with it

4 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.

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. 6d ago First seen · 114 lines · 137 tokens per session scan A 87f4d9c88033

Subscribe to this mod's changes

mcp-apps-builder is a skill published in the GitHub repository awslabs/cli-agent-orchestrator (1,213 stars, last pushed today), licensed Apache-2.0. It adds 137 tokens to every session and 1,721 once invoked, about $0.0007 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.