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 agentmods add skills/summarybotng/summarybot-ng/n8n-expression-testingnpx skills add summarybotng/summarybot-ng --skill n8n-expression-testinggit clone --depth 1 https://github.com/summarybotng/summarybot-ngWrote 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/summarybotng/summarybot-ng/n8n-expression-testing)<a href="https://agentmods.dev/skills/summarybotng/summarybot-ng/n8n-expression-testing"><img src="https://agentmods.dev/badge/skills/summarybotng/summarybot-ng/n8n-expression-testing.svg" alt="Measured on agentmods" 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 | $0.00036 | $0.02926 |
| Opus 5 | $0.00018 | $0.01463 |
| Sonnet 5 | $0.00007 | $0.00585 |
| Haiku 4.5 | $0.00004 | $0.00293 |
Grade A, and why
n8n-expression-testing scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured today.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 441 lines — stays where its author put it; the contents beside it link to each section on GitHub.
n8n Expression Testing
<default_to_action> When testing n8n expressions:
- VALIDATE syntax before execution
- TEST with multiple context scenarios
- CHECK for null/undefined handling
- VERIFY type safety
- SCAN for security vulnerabilities
Quick Expression Checklist:
- Valid JavaScript syntax
- Context variables properly referenced ($json, $node)
- Null-safe access patterns (?., ??)
- No dangerous functions (eval, Function)
- Efficient for large data sets
Common Pitfalls:
- Accessing nested properties without null checks
- Type coercion issues
- Missing fallback values
- Inefficient array operations </default_to_action>
Quick Reference Card
n8n Expression Syntax
| Pattern | Example | Description |
|---|---|---|
| Basic access | {{ $json.field }} |
Access JSON field |
| Nested access | {{ $json.user.email }} |
Access nested property |
| Array access | {{ $json.items[0] }} |
Access array element |
| Node reference | {{ $node["Name"].json.id }} |
Access other node's data |
| Method call | {{ $json.name.toLowerCase() }} |
Call string method |
| Conditional | {{ $json.x ? "yes" : "no" }} |
Ternary expression |
Context Variables
| Variable | Description | Example |
|---|---|---|
$json |
Current item data | {{ $json.email }} |
$node["Name"] |
Other node's data | {{ $node["HTTP"].json.body }} |
$items() |
Multiple items | {{ $items("Node", 0, 0).json }} |
$now |
Current timestamp | {{ $now.toISO() }} |
$today |
Today's date | {{ $today }} |
$runIndex |
Run iteration | {{ $runIndex }} |
$workflow |
Workflow info | {{ $workflow.name }} |
Expression Syntax Patterns
Safe Data Access
// BAD: Can fail if nested objects are null
{{ $json.user.profile.email }}
// GOOD: Optional chaining with fallback
{{ $json.user?.profile?.email ?? '' }}
// BAD: Array access without bounds check
{{ $json.items[0].name }}
// GOOD: Safe array access
{{ $json.items?.[0]?.name ?? 'No items' }}
What ships with it
3 files 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.
- today First seen · 441 lines · 36 tokens per session scan A d83f10fe4914
n8n-expression-testing is a skill published in the GitHub repository summarybotng/summarybot-ng (2 stars, last pushed 2mo ago), licensed MIT. It adds 36 tokens to every session and 2,926 once invoked, about $0.0002 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 2026-09-03.
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