Borrowing it
Nothing to install: this file belongs to mtnyilmaz/agents. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/mtnyilmaz/agents/main/.agents/skills/sast-xss/SKILL.mdgit clone --depth 1 https://github.com/mtnyilmaz/agentsWrote 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/mtnyilmaz/agents/sast-xss)<a href="https://agentmods.dev/skills/mtnyilmaz/agents/sast-xss"><img src="https://agentmods.dev/badge/skills/mtnyilmaz/agents/sast-xss/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/mtnyilmaz/agents/sast-xss"><img src="https://agentmods.dev/badge/skills/mtnyilmaz/agents/sast-xss.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00090 | $0.06789 |
| Opus 5 | $0.00045 | $0.03395 |
| Sonnet 5 | $0.00018 | $0.01358 |
| Haiku 4.5 | $0.00009 | $0.00679 |
Grade A, and why
sast-xss scanned grade A 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 9d 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.
Unrestricted tool accesslowExcessive agency
A wildcard tool grant or "run any command" leaves no least-privilege boundary at all.
XSS occurs when user-supplied input is incorporated into a web page's HTML, JavaScript, or DOM without proper escaping or sanitization. This allows attackers to inject and execute arbitrary scripts in victims' browsers, Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
> [curl command or browser payload to confirm the finding. How it starts
The opening of the file, as written. The whole thing — 575 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Cross-Site Scripting (XSS) Detection
You are performing a focused security assessment to find Cross-Site Scripting vulnerabilities in a codebase. This skill uses a two-phase approach with subagents: sink discovery (find all places where data is rendered into HTML, JavaScript, or the DOM without proper escaping) then taint (confirm whether user-supplied input reaches those sinks).
Prerequisites: sast/architecture.md must exist. Run the analysis skill first if it doesn't.
What is XSS
XSS occurs when user-supplied input is incorporated into a web page's HTML, JavaScript, or DOM without proper escaping or sanitization. This allows attackers to inject and execute arbitrary scripts in victims' browsers, leading to session hijacking, credential theft, defacement, and malware distribution.
The core pattern: unescaped, unsanitized user input reaches an HTML/JS output sink.
XSS Types
- Reflected XSS: User input is immediately echoed back in the HTTP response (e.g., a search term rendered directly into the page HTML).
- Stored XSS: User input is saved to persistent storage (database, file) and later rendered in HTML for other users.
- DOM-based XSS: Client-side JavaScript reads from an attacker-controlled source (
location.search,location.hash,document.cookie) and writes to a dangerous DOM sink (innerHTML,eval,document.write) without server involvement.
What XSS IS
Server-side HTML sinks — rendering user data into HTML responses without escaping:
- Python/Jinja2:
{{ var | safe }},{% autoescape off %}...{{ var }}...{% endautoescape %} - Python/Django:
mark_safe(var),format_html(...)with%sand unescaped input,{{ var | safe }}in templates - Python/Flask:
Markup(var),render_template_string(f"...{var}...") - PHP:
echo $var,print $var,<?= $var ?>withouthtmlspecialchars() - Ruby/Rails:
raw(var),var.html_safe,<%= raw var %>,content_tagwith.html_safe - Java/JSP:
<%= var %>,${var}without<c:out>orfn:escapeXml() - Java/Thymeleaf:
th:utext="${var}"(unescaped),[(${var})] - Go/html-template misuse: using
template.HTML(var),template.JS(var),template.URL(var)to bypass auto-escaping - C#/Razor:
@Html.Raw(var),MvcHtmlString.Create(var) - Node.js/EJS:
<%- var %>(unescaped), vs<%= var %>(safe) - Node.js/Handlebars:
{{{ var }}}(triple-brace, unescaped) - Node.js/Pug:
!{var}(unescaped) - Express:
res.send("<html>..." + var + "..."),res.write("<p>" + var + "</p>")
What ships with it
1 file 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.
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.
- 9d ago First seen · 575 lines · 90 tokens per session scan A 6352318e365a
sast-xss is a skill published in the GitHub repository mtnyilmaz/agents (6 stars, last pushed 3mo ago), licensed MIT. It adds 90 tokens to every session and 6,789 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 2 findings (unrestricted tool access, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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