Defense In Depth
sandgardenhq/sgai
A skill your agent uses when invalid data causes failures deep in execution, requiring validation at multiple system layers - validates at every layer data passes through to make bugs structurally…
Validate at every layer data passes through to make bugs impossible.
Install Defense In Depth Validation
$ npx skills add secondsky/claude-skills --skill defense-in-depth-validation -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install secondsky/claude-skills defense-in-depth-validation --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/defense-in-depth-validation/skills/defense-in-depth-validation .claude/skills/defense-in-depth-validation && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "defense-in-depth-validation" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/defense-in-depth-validation/skills/defense-in-depth-validation into .claude/skills/defense-in-depth-validation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "defense-in-depth-validation", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/secondsky/claude-skills/tree/main/plugins/defense-in-depth-validation/skills/defense-in-depth-validationType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add secondsky/claude-skills --skill defense-in-depth-validation -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install secondsky/claude-skills defense-in-depth-validation --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .agents/skills && cp -r skills-src/plugins/defense-in-depth-validation/skills/defense-in-depth-validation .agents/skills/defense-in-depth-validation && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "defense-in-depth-validation" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/defense-in-depth-validation/skills/defense-in-depth-validation into .agents/skills/defense-in-depth-validation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "defense-in-depth-validation", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add secondsky/claude-skills --skill defense-in-depth-validation -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install secondsky/claude-skills defense-in-depth-validation --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/plugins/defense-in-depth-validation/skills/defense-in-depth-validation .cursor/skills/defense-in-depth-validation && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "defense-in-depth-validation" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/defense-in-depth-validation/skills/defense-in-depth-validation into .cursor/skills/defense-in-depth-validation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "defense-in-depth-validation", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/secondsky/claude-skills.git --path plugins/defense-in-depth-validation/skills/defense-in-depth-validation--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add secondsky/claude-skills --skill defense-in-depth-validation -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install secondsky/claude-skills defense-in-depth-validation --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/plugins/defense-in-depth-validation/skills/defense-in-depth-validation .gemini/skills/defense-in-depth-validation && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "defense-in-depth-validation" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/defense-in-depth-validation/skills/defense-in-depth-validation into .gemini/skills/defense-in-depth-validation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "defense-in-depth-validation", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install secondsky/claude-skills defense-in-depth-validationInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add secondsky/claude-skills --skill defense-in-depth-validation -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .github/skills && cp -r skills-src/plugins/defense-in-depth-validation/skills/defense-in-depth-validation .github/skills/defense-in-depth-validation && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "defense-in-depth-validation" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/defense-in-depth-validation/skills/defense-in-depth-validation into .github/skills/defense-in-depth-validation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "defense-in-depth-validation", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add secondsky/claude-skills --skill defense-in-depth-validation -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install secondsky/claude-skills defense-in-depth-validation --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/plugins/defense-in-depth-validation/skills/defense-in-depth-validation .opencode/skills/defense-in-depth-validation && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "defense-in-depth-validation" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/defense-in-depth-validation/skills/defense-in-depth-validation into .opencode/skills/defense-in-depth-validation/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "defense-in-depth-validation", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
defense-in-depth-validation- GitHub stars
- 227
- Token cost
- ~1.3k tokens
- SKILL.md length
- 447 words
- Files
- 1
- Skills in repo
- 169
- Repo updated
- First seen
- Licence
- MIT
At a glance
Validate at every layer data passes through to make bugs impossible.
- Works in 4 steps: Trace the data flow - Where does bad… → Map all checkpoints - List every point… → Add validation at each layer - Entry,… → …
- Invalid data causes failures deep in execution
- SKILL.md covers Overview, Why Multiple Layers, The Four Layers and Applying the Pattern, plus 3 more sections
- Calls git
What it does
Defense In Depth Validation is an agent skill from secondsky/claude-skills. Validate at every layer data passes through to make bugs impossible. Use when invalid data causes failures deep in execution, requiring validation at multiple system layers.
Its SKILL.md is about 1.3k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.
It sits in Security, covering Secure coding. It works with Git. The repository describes itself as: Production-ready skills for Claude Code CLI - Cloudflare, React, Tailwind v4, and AI integrations. The licence is MIT.
When your agent uses it
- Invalid data causes failures deep in execution
- Requiring validation at multiple system layers
Example prompts
- “/defense-in-depth-validation”
Workflow steps
4 steps, taken from the first numbered list in SKILL.md.
- Trace the data flow - Where does bad value originate? Where used?
- Map all checkpoints - List every point data passes through
- Add validation at each layer - Entry, business, environment, debug
- Test each layer - Try to bypass layer 1, verify layer 2 catches it
What it can do on your machine
Read from SKILL.md and the folder at commit 8837836. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
Shell commands in SKILL.md call:
git
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md. Its commands use git, which can reach the network depending on how they are called.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
Defense In Depth Validation loads about 1.3k tokens when it runs. Until then it costs about 50 tokens; SKILL.md has 447 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from secondsky/claude-skills at commit 8837836, republished under its MIT licence (© secondsky). 447 words, ~1,329 tokens.
Download SKILL.mdSave it as
.claude/skills/defense-in-depth-validation/SKILL.md (or your agent's skills folder).- name
- defense-in-depth-validation
- description
- Validate at every layer data passes through to make bugs impossible. Use when invalid data causes failures deep in execution, requiring validation at multiple system layers.
- metadata.version
- 1.1.0
- license
- MIT
Defense-in-Depth Validation
Overview
When you fix a bug caused by invalid data, adding validation at one place feels sufficient. But that single check can be bypassed by different code paths, refactoring, or mocks.
Core principle: Validate at EVERY layer data passes through. Make the bug structurally impossible.
Why Multiple Layers
Single validation: "We fixed the bug" Multiple layers: "We made the bug impossible"
Different layers catch different cases:
- Entry validation catches most bugs
- Business logic catches edge cases
- Environment guards prevent context-specific dangers
- Debug logging helps when other layers fail
The Four Layers
Layer 1: Entry Point Validation
Purpose: Reject obviously invalid input at API boundary
function createProject(name: string, workingDirectory: string) {
if (!workingDirectory || workingDirectory.trim() === '') {
throw new Error('workingDirectory cannot be empty');
}
if (!existsSync(workingDirectory)) {
throw new Error(`workingDirectory does not exist: ${workingDirectory}`);
}
if (!statSync(workingDirectory).isDirectory()) {
throw new Error(`workingDirectory is not a directory: ${workingDirectory}`);
}
// ... proceed
}Layer 2: Business Logic Validation
Purpose: Ensure data makes sense for this operation
function initializeWorkspace(projectDir: string, sessionId: string) {
if (!projectDir) {
throw new Error('projectDir required for workspace initialization');
}
// ... proceed
}Layer 3: Environment Guards
Purpose: Prevent dangerous operations in specific contexts
async function gitInit(directory: string) {
// In tests, refuse git init outside temp directories
if (process.env.NODE_ENV === 'test') {
const normalized = normalize(resolve(directory));
const tmpDir = normalize(resolve(tmpdir()));
if (!normalized.startsWith(tmpDir)) {
throw new Error(
`Refusing git init outside temp dir during tests: ${directory}`
);
}
}
// ... proceed
}Layer 4: Debug Instrumentation
Purpose: Capture context for forensics
async function gitInit(directory: string) {
const stack = new Error().stack;
logger.debug('About to git init', {
directory,
cwd: process.cwd(),
stack,
});
// ... proceed
}Applying the Pattern
When you find a bug:
- Trace the data flow - Where does bad value originate? Where used?
- Map all checkpoints - List every point data passes through
- Add validation at each layer - Entry, business, environment, debug
- Test each layer - Try to bypass layer 1, verify layer 2 catches it
Example from Session
Bug: Empty projectDir caused git init in source code
Data flow:
- Test setup → empty string
Project.create(name, '')WorkspaceManager.createWorkspace('')git initruns inprocess.cwd()
Four layers added:
- Layer 1:
Project.create()validates not empty/exists/writable - Layer 2:
WorkspaceManagervalidates projectDir not empty - Layer 3:
WorktreeManagerrefuses git init outside tmpdir in tests - Layer 4: Stack trace logging before git init
Result: All 1847 tests passed, bug impossible to reproduce
Show full SKILL.md (182 more words)Show less
Key Insight
All four layers were necessary. During testing, each layer caught bugs the others missed:
- Different code paths bypassed entry validation
- Mocks bypassed business logic checks
- Edge cases on different platforms needed environment guards
- Debug logging identified structural misuse
Don't stop at one validation point. Add checks at every layer.
Security defense-in-depth
The same layered approach is the standard pattern for security controls: trust is never granted at a single point, so that a bug or bypass in any one layer cannot by itself compromise the system. Each request is checked independently at the edge, in the handler, and at the data layer.
- Layer 1 (edge): rate-limit and filter at the edge (CDN/WAF such as Cloudflare or AWS WAF) so abusive traffic never reaches the origin.
- Layer 2 (handler): re-derive authorization server-side from the session
— never trust a client-supplied claim like a
userIdin the body. - Layer 3 (data): enforce the ownership invariant in the database query so that even a handler bug cannot cross tenant boundaries.
// Layer 2 — re-derive authz server-side, never trust client claims
app.put('/docs/:id', async (req, res) => {
const user = await verifySession(req.cookies.session); // throws if invalid
// Layer 3 — DB clause re-checks ownership; a handler bug still can't cross tenants
const updated = await db.query(
'UPDATE docs SET title = $1 WHERE id = $2 AND owner_id = $3 RETURNING *',
[req.body.title, req.params.id, user.id]
);
if (!updated.rowCount) return res.status(403).send('Not allowed');
res.json(updated.rows[0]);
});Defense in depth means no single layer's failure is sufficient to compromise the system.
© secondsky, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
Just SKILL.md in plugins/defense-in-depth-validation/skills/defense-in-depth-validation of secondsky/claude-skills.
Open the folder on GitHubat commit 8837836
Compare with similar skills
Defense In Depth Validation next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Defense In Depth Validation this skillsecondsky/claude-skills | 227 | — | ~1.3k | Automated safety check: Pass | MIT | |
| Defense In Depthsandgardenhq/sgai | 137 | 3 repos | ~970 | Automated safety check: Pass | Custom licence | |
| Thorough Code Reviewpretend1111/claude-desktop-app | 494 | 1 repos | ~502 | Automated safety check: Pass | Custom licence | |
| Security AuditTheDecipherist/claude-code-mastery | 550 | — | ~1.3k | Automated safety check: Notes | MIT | |
| Humble Header Report Analystrfc-st/humble | 379 | — | ~3.7k | Automated safety check: Pass | MIT | |
| Pre-Commit Security Scanzereight/gitlab-mcp | 2k | 1 repos | ~859 | Automated safety check: Notes | MIT |
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pretend1111/claude-desktop-app
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Security Audit
TheDecipherist/claude-code-mastery
Checks a codebase for hardcoded secrets, vulnerable dependencies, weak input handling, weak authentication and unsafe transport settings before deployment or merge.
Humble Header Report Analyst
rfc-st/humble
Parses reports from the humble HTTP security header analyzer and explains each finding with remediation steps for DevOps teams.
Pre-Commit Security Scan
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Runs a fast security sweep of recent code changes before a commit or PR, checking for leaked secrets, vulnerable dependencies, unsafe input handling and auth gaps.
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Works with
Categories
Questions about Defense In Depth Validation
What does Defense In Depth Validation do?
Validate at every layer data passes through to make bugs impossible. Defense In Depth Validation is an agent skill from secondsky/claude-skills. Validate at every layer data passes through to make bugs impossible.
When should I use Defense In Depth Validation?
Defense In Depth Validation fits situations like: invalid data causes failures deep in execution; requiring validation at multiple system layers.
How do I install Defense In Depth Validation in Claude Code?
Run `npx skills add secondsky/claude-skills --skill defense-in-depth-validation -a claude-code`. Or copy the skill folder (plugins/defense-in-depth-validation/skills/defense-in-depth-validation in secondsky/claude-skills) into .claude/skills/defense-in-depth-validation in your project. Claude Code loads it when a task matches its description.
How do I install Defense In Depth Validation in Codex?
Run `npx skills add secondsky/claude-skills --skill defense-in-depth-validation -a codex`. Or copy the skill folder (plugins/defense-in-depth-validation/skills/defense-in-depth-validation in secondsky/claude-skills) into .agents/skills/defense-in-depth-validation in your project. Codex loads it when a task matches its description.
Can I use Defense In Depth Validation in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add secondsky/claude-skills --skill defense-in-depth-validation -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/defense-in-depth-validation, .gemini/skills/defense-in-depth-validation, .github/skills/defense-in-depth-validation and .opencode/skills/defense-in-depth-validation in your project.
What does Defense In Depth Validation need to run?
Going by SKILL.md and its folder, Defense In Depth Validation needs the command-line tools its instructions call (git).
Does Defense In Depth Validation access the network?
SKILL.md contains no URLs. Its commands use git, which can reach the network depending on how they are called. This is read from the text; nothing was executed.
Is Defense In Depth Validation safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does Defense In Depth Validation use?
Defense In Depth Validation is published under the MIT licence (declared in SKILL.md). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Defense In Depth Validation use?
About 1.3k tokens (SKILL.md is roughly 5.3k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.
What are the alternatives to Defense In Depth Validation?
Skills that share tags, products or a category with Defense In Depth Validation: Defense In Depth (sandgardenhq/sgai, 137 stars), Thorough Code Review (pretend1111/claude-desktop-app, 494 stars), Security Audit (TheDecipherist/claude-code-mastery, 550 stars) and Humble Header Report Analyst (rfc-st/humble, 379 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Defense In Depth Validation?
secondsky (a GitHub user) maintains it in secondsky/claude-skills, which has 227 GitHub stars. The repository holds 169 skills in this directory. The repository was last updated on September 28, 2026.
Source: secondsky/claude-skills on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.