monaco-component-testing

monaco-component-testing is a skill for Claude Code, Codex from RedHatInsights/nxtcm-components. It costs 19 tokens per session (4,809 once invoked), scanned A, original, Apache-2.0.

A guide for testing Monaco, a browser-based code editor, inside Playwright component tests. It explains the editor's event limitations and recommends testing different behavior at different test levels.

In plain words
What is it for?
Use it to test YAML or code-editor components, validation messages, syntax errors, error markers, and the boundary between component and end-to-end tests.
Why use it?
It helps avoid tests that appear to run but never trigger validation because Monaco's setValue method does not fire change events. It clarifies how to test errors, schema checks, and editor behavior reliably.

Skill for Claude CodeCodex

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/redhatinsights/nxtcm-components/monaco-component-testing
Any agent
npx skills add RedHatInsights/nxtcm-components --skill monaco-component-testing
Clone the repo
git clone --depth 1 https://github.com/RedHatInsights/nxtcm-components

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 monaco-component-testing

README.md
[![agentmods](https://agentmods.dev/badge/skills/redhatinsights/nxtcm-components/monaco-component-testing.svg)](https://agentmods.dev/skills/redhatinsights/nxtcm-components/monaco-component-testing)
Your own site
<a href="https://agentmods.dev/skills/redhatinsights/nxtcm-components/monaco-component-testing"><img src="https://agentmods.dev/badge/skills/redhatinsights/nxtcm-components/monaco-component-testing.svg" alt="Measured on agentmods" height="20"></a>
Per session 19 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 4,809 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 $0.00019 $0.04809
Opus 5 $0.00010 $0.02405
Sonnet 5 $0.00004 $0.00962
Haiku 4.5 $0.00002 $0.00481

Measured 4d ago against content hash b476d4a53d8d, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

monaco-component-testing 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 4d 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.

.agents/skills/monaco-component-testing/SKILL.md · 744 lines

How it starts

The opening of the file, as written. The whole thing — 744 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Monaco Editor Component Testing Guide

Comprehensive guide for testing Monaco editor components in Playwright Component Tests (CT), including known limitations, testing strategies, and best practices learned from YAML editor implementation.

When to Use This Skill

Invoke this skill when:

  • Testing components that use Monaco editor (CodeEditor, YAML editor, etc.)
  • Planning test strategy for Monaco integration
  • Debugging flaky Monaco tests
  • Understanding why validation tests fail in CT
  • Deciding which layer to test Monaco functionality

Related skills:

  • .agents/skills/monaco-e2e-testing/SKILL.md - E2E testing for Monaco (different constraints)

Critical Monaco Testing Limitations

Limitation 1: setValue() Does NOT Trigger onChange

The Problem: Monaco's setValue() method does not fire the onChange event that validation logic depends on.

// ❌ This DOES NOT work in Playwright CT
await monacoEditor.evaluate((node) => {
  const editor = (window as any).monacoEditor;
  editor.setValue(invalidYaml); // onChange NOT triggered!
});

// Validation handler NEVER fires
// Error markers NEVER appear
// Error banner NEVER displays

Impact:

  • Cannot test validation logic via Monaco in CT
  • Cannot test error markers appearing in editor
  • Cannot test error banner display
  • Cannot test debounced validation

Solution: Test validation logic separately in unit tests (see Testing Strategy below)


Limitation 2: Complex DOM Structure Causes Click Interception

The Problem: Monaco creates multiple overlapping DOM layers (editor, overlays, minimap, margins) that intercept click events.

// ❌ These clicks are FLAKY in CT
await component.locator('.monaco-editor').click(); // Intercepted by overlay
await component.locator('button').click();          // Intercepted by editor
await component.locator('.monaco-editor textarea').click(); // Intercepted by margin

Playwright Error:

<div>…</div> from <div class="margin">…</div> subtree intercepts pointer events
<body>…</body> intercepts pointer events

Read the full file on GitHub · 744 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. 4d ago First seen · 744 lines · 19 tokens per session scan A b476d4a53d8d

Subscribe to this mod's changes

monaco-component-testing is a skill published in the GitHub repository RedHatInsights/nxtcm-components (3 stars, last pushed 2d ago), licensed Apache-2.0. It adds 19 tokens to every session and 4,809 once invoked, about $0.0001 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 2026-08-31.

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