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/jpm1118/threadwork/defense-in-depthnpx skills add JPM1118/Threadwork --skill defense-in-depthgit clone --depth 1 https://github.com/JPM1118/ThreadworkWrote 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/jpm1118/threadwork/defense-in-depth)<a href="https://agentmods.dev/skills/jpm1118/threadwork/defense-in-depth"><img src="https://agentmods.dev/badge/skills/jpm1118/threadwork/defense-in-depth.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 | $0.00000 | $0.02168 |
| Opus 5 | $0.00000 | $0.01084 |
| Sonnet 5 | $0.00000 | $0.00434 |
| Haiku 4.5 | $0.00000 | $0.00217 |
Grade A, and why
defense-in-depth 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 4d 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 — 353 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Defense-in-Depth Skill
Make bugs "structurally impossible" by validating at every layer data traverses.
Core Principle
VALIDATE AT EVERY LAYER
Don't assume data is valid just because it passed a previous check. Each layer defends itself.
When to Use This Skill
Use this skill when:
- Implementing any feature that handles external data
- Adding validation after fixing a bug
- Reviewing code for robustness
- Designing API boundaries
- After root-cause analysis reveals missing validation
The Four Validation Layers
┌─────────────────────────────────────────────────────────────┐
│ Defense-in-Depth Layers │
├─────────────────────────────────────────────────────────────┤
│ │
│ Layer 1: ENTRY POINT VALIDATION │
│ ↓ Reject invalid input at API boundaries │
│ │
│ Layer 2: BUSINESS LOGIC VALIDATION │
│ ↓ Ensure semantic correctness │
│ │
│ Layer 3: ENVIRONMENT GUARDS │
│ ↓ Prevent dangerous operations in contexts │
│ │
│ Layer 4: DEBUG INSTRUMENTATION │
│ Capture context for forensic analysis │
│ │
└─────────────────────────────────────────────────────────────┘
Layer 1: Entry Point Validation
Where: API endpoints, message handlers, file parsers, CLI inputs
Purpose: Reject malformed data before it enters the system
What to Validate
| Check | Example |
|---|---|
| Required fields present | if (!request.userId) throw ValidationError |
| Types are correct | if (typeof amount !== 'number') |
| Values in range | if (age < 0 || age > 150) |
| Format is valid | if (!email.match(emailRegex)) |
| Size within limits | if (file.size > MAX_FILE_SIZE) |
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.
- 4d ago First seen · 353 lines · 0 tokens per session scan A 67aadcab142a
defense-in-depth is a skill published in the GitHub repository JPM1118/Threadwork (5 stars, last pushed 8mo ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 2,168 tokens. 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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