webapp-testing

webapp-testing is a skill for Claude Code from Zandereins/schliff. It costs 35 tokens per session (884 once invoked), scanned A, a copy of webapp-testing, MIT.

A toolkit for testing local web applications in a real browser with Playwright, including checks of page behavior and browser output.

In plain words
What is it for?
It is for checking web app features, investigating UI problems, taking screenshots, and reading browser logs.
Why use it?
It helps find broken frontend behavior by running browser checks and showing what the page looks like and what the browser reports.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin.

Needs its repository: it runs a file that does not travel with it, so clone the repository first. The line is ├─ No → Run: python scripts/with_server.py --help.

Part of the schliff plugin — 18 skills, 1 hook shipped together

Good fit It is for checking web app features, investigating UI problems, taking screenshots, and reading browser logs.

Compare 6 skills from other repositories ↓
Install

Getting it into your agent

It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.

Clone the repo
git clone --depth 1 https://github.com/Zandereins/schliff
agentmods
npx agentmods add skills/zandereins/schliff/01-webapp-testing

Made for: Claude Code.

Or install schliff, the plugin that ships this one along with the rest of its 18 skills, 1 hook.

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 webapp-testing

README.md
[![agentmods](https://agentmods.dev/badge/skills/zandereins/schliff/01-webapp-testing/github.svg)](https://agentmods.dev/skills/zandereins/schliff/01-webapp-testing)
Your own site
<a href="https://agentmods.dev/skills/zandereins/schliff/01-webapp-testing"><img src="https://agentmods.dev/badge/skills/zandereins/schliff/01-webapp-testing/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 webapp-testing

Your own site · 80×15
<a href="https://agentmods.dev/skills/zandereins/schliff/01-webapp-testing"><img src="https://agentmods.dev/badge/skills/zandereins/schliff/01-webapp-testing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 35 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 884 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin 98% copy Near-identical to another mod 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 $0.00035 $0.00884
Opus 5 $0.00017 $0.00442
Sonnet 5 $0.00007 $0.00177
Haiku 4.5 $0.00003 $0.00088

Measured 5d ago against content hash 51b7349e77ec, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

webapp-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 5d 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.

Origin

This is a copy

98% identical to webapp-testing — 2 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

benchmarks/corpus/v1/phase0-snapshot/01-webapp-testing.SKILL.md · 96 lines

How it starts

The opening of the file, as written. The whole thing — 96 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Web Application Testing

To test local web applications, write native Python Playwright scripts.

Helper Scripts Available:

  • scripts/with_server.py - Manages server lifecycle (supports multiple servers)

Always run scripts with --help first to see usage. DO NOT read the source until you try running the script first and find that a customized solution is abslutely necessary. These scripts can be very large and thus pollute your context window. They exist to be called directly as black-box scripts rather than ingested into your context window.

Decision Tree: Choosing Your Approach

User task → Is it static HTML?
    ├─ Yes → Read HTML file directly to identify selectors
    │         ├─ Success → Write Playwright script using selectors
    │         └─ Fails/Incomplete → Treat as dynamic (below)
    │
    └─ No (dynamic webapp) → Is the server already running?
        ├─ No → Run: python scripts/with_server.py --help
        │        Then use the helper + write simplified Playwright script
        │
        └─ Yes → Reconnaissance-then-action:
            1. Navigate and wait for networkidle
            2. Take screenshot or inspect DOM
            3. Identify selectors from rendered state
            4. Execute actions with discovered selectors

Example: Using with_server.py

To start a server, run --help first, then use the helper:

Single server:

python scripts/with_server.py --server "npm run dev" --port 5173 -- python your_automation.py

Multiple servers (e.g., backend + frontend):

python scripts/with_server.py \
  --server "cd backend && python server.py" --port 3000 \
  --server "cd frontend && npm run dev" --port 5173 \
  -- python your_automation.py

To create an automation script, include only Playwright logic (servers are managed automatically):

from playwright.sync_api import sync_playwright

with sync_playwright() as p:
    browser = p.chromium.launch(headless=True) # Always launch chromium in headless mode
    page = browser.new_page()
    page.goto('http://localhost:5173') # Server already running and ready
    page.wait_for_load_state('networkidle') # CRITICAL: Wait for JS to execute
    # ... your automation logic
    browser.close()

Read the full file on GitHub · 96 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. 5d ago First seen · 96 lines · 35 tokens per session scan A 51b7349e77ec

Subscribe to this mod's changes

webapp-testing is a skill published in the GitHub repository Zandereins/schliff (15 stars, last pushed yesterday), licensed MIT. It adds 35 tokens to every session and 884 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 98% identical to webapp-testing, differing in 2 lines, and is treated as a copy.

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