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 rafayqazi/mercari-jp-mcp --skill mercari-gui-embedded-jsgit clone --depth 1 https://github.com/rafayqazi/mercari-jp-mcpWrote 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/rafayqazi/mercari-jp-mcp/mercari-gui-embedded-js)<a href="https://agentmods.dev/skills/rafayqazi/mercari-jp-mcp/mercari-gui-embedded-js"><img src="https://agentmods.dev/badge/skills/rafayqazi/mercari-jp-mcp/mercari-gui-embedded-js/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/rafayqazi/mercari-jp-mcp/mercari-gui-embedded-js"><img src="https://agentmods.dev/badge/skills/rafayqazi/mercari-jp-mcp/mercari-gui-embedded-js.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 | $0.00071 | $0.00993 |
| Opus 5 | $0.00036 | $0.00496 |
| Sonnet 5 | $0.00014 | $0.00199 |
| Haiku 4.5 | $0.00007 | $0.00099 |
Grade A, and why
mercari-gui-embedded-js 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 12d 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.
How it starts
The opening of the file, as written. The whole thing — 89 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Mercari GUI — embedded JavaScript in Python
The Flask UI lives in mercari_gui.py as HTML_PAGE = u'''...'''. All client logic is one inline <script>. One syntax error anywhere in that script prevents the entire block from parsing — tabs, search buttons, and bulk streaming all stop working with no obvious server error.
Golden rule: Python string vs JavaScript string
Inside HTML_PAGE, you are writing Python source that must emit valid JavaScript.
| You want in the browser (JS) | Write in mercari_gui.py (Python) |
|---|---|
Newline character in JS: '\n' |
'\\n' |
Split on blank line: '\n\n' |
'\\n\\n' |
| Backslash in JS string | '\\\\' (only when needed) |
Never use bare '\n' or '\n\n' inside the HTML/JS portion of HTML_PAGE. Python treats \n as a real line break in the string, which splits JS string literals across physical lines and causes SyntaxError: Invalid or unexpected token.
Wrong → broken output
Python source (wrong):
text.split('\n')
data.keywords.join('\n')
buffer.split('\n\n')
let csv = 'Header\n';
Rendered JS (broken — string literal split across lines):
text.split('
')
Right
text.split('\\n')
data.keywords.join('\\n')
buffer.split('\\n\\n')
let csv = 'Header\\n';
csv += row + '"\\n';
Plain Python code outside HTML_PAGE (e.g. joined = '\n'.join(texts)) uses normal Python '\n' — do not double-escape there.
Other escaping in this file
&in JS strings inside HTML: Use HTML entities in the embedded HTML/JS text when the character would break HTML parsing, e.g.Loading & translating...not raw&inside attribute-like contexts.- Item IDs in dynamic HTML: Prefer
data-item-id="..."+ delegated click handlers (see bottom of script). Avoid fragileonclick="fetchDescription('...')"with nested quotes. - Tabs: Use
data-tab+switchTab(name); tab panel ids aretab+ PascalCase suffix (bulk→tabBulk,yahooBulk→tabYahooBulk).
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.
- 12d ago First seen · 89 lines · 71 tokens per session scan A fdb6341f4e04
mercari-gui-embedded-js is a skill published in the GitHub repository rafayqazi/mercari-jp-mcp (0 stars, last pushed 1mo ago), licensed MIT. It adds 71 tokens to every session and 993 once invoked, about $0.0004 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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