Fullstack Guardian

What it does

When your agent uses it

• Building a feature that spans the database, API and UI in one pass
• Adding an authenticated REST endpoint together with its form or view
• Checking a feature design for gaps in auth, validation and output encoding
• Choosing between a monolith and microservices for a new project
• Preparing a finished feature for handoff to QA and deployment

Example prompts

• “Build a CRUD screen for customer notes with the API, form validation and permission checks.”
• “Write the design doc for the invite-a-teammate feature before touching any code.”
• “Walk through the security checklist for our new file upload endpoint.”
• “Decide whether the reporting module should stay in the monolith or become its own service.”

Workflow steps

6 steps, taken from the first numbered list in SKILL.md.

1. 1Gather requirements - Understand feature scope and acceptance criteria
2. 2Design solution - Consider all three perspectives (Frontend/Backend/Security)
3. 3Write technical design - Document approach in specs/{feature}_design.md
4. 4Security checkpoint - Run through references/security-checklist.md before writing any code; confirm auth, authz, validation, and output…
5. 5Implement - Build incrementally, testing each component as you go
6. 6Hand off - Pass to Test Master for QA, DevOps for deployment

What it can do on your machine

Read from SKILL.md and the folder at commit 1be15d8. 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

  No scripts in the folder and no shell commands in SKILL.md (its code samples are python and typescript).

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • github.com
  • synergetic.solutions
  • jeffallan.github.io

  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

Fullstack Guardian loads about 1.5k tokens when it runs, and up to ~17k if it reads all its reference files. Until then it costs about 236 tokens; SKILL.md has 349 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~236

When it runs · the whole SKILL.md, loaded when a task matches

~1.5k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~17k

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

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 Jeffallan/claude-skills at commit 1be15d8, republished under its MIT licence (© Jeffallan). 349 words, ~1,496 tokens.

name

fullstack-guardian

description

Builds security-focused full-stack web applications by implementing integrated frontend and backend components with layered security at every level. Covers the complete stack from database to UI, enforcing auth, input validation, output encoding, and parameterized queries across all layers. Use when implementing features across frontend and backend, building REST APIs with corresponding UI, connecting frontend components to backend endpoints, creating end-to-end data flows from database to UI, or implementing CRUD operations with UI forms. Distinct from frontend-only, backend-only, or API-only skills in that it simultaneously addresses all three perspectives—Frontend, Backend, and Security—within a single implementation workflow. Invoke for full-stack feature work, web app development, authenticated API routes with views, microservices, real-time features, monorepo architecture, or technology selection decisions.

license

MIT

metadata.author

https://github.com/Jeffallan

metadata.company

https://synergetic.solutions

metadata.version

1.1.1

metadata.domain

security

metadata.triggers

fullstack, implement feature, build feature, create API, frontend and backend, full stack, new feature, implement, microservices, websocket, real-time…

metadata.role

expert

metadata.scope

implementation

metadata.output-format

code

metadata.related-skills

feature-forge, test-master, devops-engineer, secure-code-guardian, architecture-designer, react-expert, typescript-pro

@router.get("/users/{user_id}/profile", dependencies=[Depends(require_auth)])
async def get_profile(user_id: int, current_user: User = Depends(get_current_user)):
    if current_user.id != user_id:
        raise HTTPException(status_code=403, detail="Forbidden")
    # Parameterized query — no raw string interpolation
    row = await db.fetchone("SELECT id, name, email FROM users WHERE id = ?", (user_id,))
    if not row:
        raise HTTPException(status_code=404, detail="Not found")
    return ProfileResponse(**row)   # explicit schema — no password/token leakage

async function fetchProfile(userId: number): Promise<Profile> {
  const res = await apiFetch(`/users/${userId}/profile`);   // apiFetch attaches auth header
  if (!res.ok) throw new Error(await res.text());
  return res.json();
}
// Client-side input guard (never the only guard)
if (!Number.isInteger(userId) || userId <= 0) throw new Error("Invalid user ID");

© Jeffallan, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 10 other files (references) in skills/fullstack-guardian of Jeffallan/claude-skills.

• SKILL.md
• references/api-design-standards.md
• references/architecture-decisions.md
• references/backend-patterns.md
• references/common-patterns.md
• references/deliverables-checklist.md
• references/design-template.md
• references/error-handling.md
• references/frontend-patterns.md
• references/integration-patterns.md
• references/security-checklist.md

Open the folder on GitHubat commit 1be15d8