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Building OpenAI Apps with Stateless MCP Servers · coco-research | DecimalAI

agent toolingby coco-research

Building OpenAI Apps with Stateless MCP Servers

coco-research/OpenAI Apps MCP

Source coco-research/coco ↗License NOASSERTION

Build ChatGPT apps with MCP servers on Cloudflare Workers. Extend ChatGPT with custom tools and interactive widgets (HTML/JS UI).

SkillScore100Maintained

Automatic

AI Engineer pack

Last verified 8/30/2026

What it changes

Passed 23 of 23 test cases with the skill, and 12 of 23 without it.

Without skill52%

With skill100%

Checks it passed that the model alone missed

Uses the ui://widget/ URI scheme prefix.
Sets the assets binding property name to ASSETS.
Identifies version 1.25.3 as the fixed SDK version.

and 15 more in the full report

11 fixed12 passed either way0 still failing0 broke

Pass-rate lift: +48 pp
Tokens: +129%
Agent turns: 0%
Response time: -39%

Model gemini-3.6-flashMeasured 8/30/2026v123 of 23 cases passed with skill

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/coco-research-openai-apps-mcp/SKILL.md https://app.decimal.ai/s/coco-research-openai-apps-mcp/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add coco-research-openai-apps-mcp, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/coco-research-openai-apps-mcp/ and pins it in .decimal/skills.lock

decimalai skills add coco-research-openai-apps-mcp

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/coco-research-openai-apps-mcp/SKILL.md https://app.decimal.ai/s/coco-research-openai-apps-mcp/SKILL.md

Raw file: /s/coco-research-openai-apps-mcp/SKILL.md ↗ · machine-readable summary at /s/coco-research-openai-apps-mcp.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

One of 11 test cases the skill fixed. Same model, same prompt, with and without the skill.

1 of 11

Prompt

When annotating a tool's outputTemplate, my team configured the path as 'https://my-domain.com/widgets/map.html'. However, ChatGPT fails to map the tool output to the widget resource. What exact URI prefix scheme must be used in the outputTemplate annotation?

What was checked, without and with the skill
Checked	Without skill	With skill
Uses the ui://widget/ URI scheme prefix.	Missed	Passed

case-09 · gemini-3.6-flash · 8/30/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md499 lines5 filesincludes scripts

Building OpenAI Apps with Stateless MCP Servers

Status: Production Ready Last Updated: 2026-01-21 Dependencies: cloudflare-worker-base, hono-routing (optional) Latest Versions: @modelcontextprotocol/[email protected], [email protected], [email protected], [email protected]

Overview

Build ChatGPT Apps using MCP (Model Context Protocol) servers on Cloudflare Workers. Extends ChatGPT with custom tools and interactive widgets (HTML/JS UI rendered in iframe).

Architecture: ChatGPT → MCP endpoint (JSON-RPC 2.0) → Tool handlers → Widget resources (HTML)

Status: Apps available to Business/Enterprise/Edu (GA Nov 13, 2025). MCP Apps Extension (SEP-1865) formalized Nov 21, 2025.

Quick Start

1. Scaffold & Install

npm create cloudflare@latest my-openai-app -- --type hello-world --ts --git --deploy false
cd my-openai-app
npm install @modelcontextprotocol/[email protected] [email protected] [email protected]
npm install -D @cloudflare/[email protected] [email protected]

2. Configure wrangler.jsonc

{
  "name": "my-openai-app",
  "main": "dist/index.js",
  "compatibility_flags": ["nodejs_compat"],  // Required for MCP SDK
  "assets": {
    "directory": "dist/client",
    "binding": "ASSETS"  // Must match TypeScript

Track record

Benchmark

23 / 23

test cases passed, vs 12 / 23 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v4 — 8/10/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

coco-research / coco

skills/openai-apps-mcp/SKILL.md

View on GitHub ↗

License NOASSERTIONImported 8/10/2026Version v1Bundled 4 files · scripts

More skills from the same source and nearby in the registry, with their headline benchmark lift.

Ready to supercharge your AI agents?

See it in action

What's inside

Building OpenAI Apps with Stateless MCP Servers

Overview

Quick Start

1. Scaffold & Install

2. Configure wrangler.jsonc

Track record

Benchmark

Adoption

SkillSafety

Source

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