validation

A guide for validating application input with Zod 4, a library for describing and checking data shapes. It covers schemas for API requests and configuration, including format checks, length limits, and normalization.

In plain words
What is it for?
Use it when adding or reviewing validation for API routes, configuration, emails, URLs, UUIDs, and similar fields.
Why use it?
It helps reject invalid input at the route boundary and keeps validation rules organized. It also prevents use of older Zod syntax where newer standalone validators are required.

Skill for Claude CodeCodex

Install

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.

agentmods
npx agentmods add skills/qauth-labs/qauth/validation
Any agent
npx skills add qauth-labs/qauth --skill validation
Clone the repo
git clone --depth 1 https://github.com/qauth-labs/qauth

Made for: Claude Code, Codex.

Per session 60 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 913 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00060 $0.00913
Opus 5 $0.00030 $0.00456
Sonnet 5 $0.00012 $0.00183
Haiku 4.5 $0.00006 $0.00091

Measured 2d ago against content hash 2e12335a9aad, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

validation 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 2d 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.

.claude/skills/validation/SKILL.md · 101 lines

How it starts

The opening of the file, as written. The whole thing — 101 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Validation (QAuth)

Input validation for the QAuth auth-server using Zod v4. Validate at the route boundary (fail fast), organize schemas consistently, and use the standalone Zod v4 validators. Use this skill when defining or reviewing schemas.

Zod v4 Validators

This project uses Zod v4, where many format validators are standalone functions, not string methods. Do not use the deprecated string-method form.

Use Not
z.email() z.string().email()
z.uuid() z.string().uuid()
z.url() z.string().url()

Optional error message: z.email('Invalid email format'), z.uuid('Invalid realm ID format'), z.url('Must be a valid URL').

Also standalone in Zod v4: z.httpUrl(), z.hostname(), z.jwt(), z.iso.date(), z.iso.datetime(), z.ipv4(), z.ipv6(), z.hex(), z.base64(), etc. See zod.dev/api under "String formats." If you learn another Zod v4 standalone validator, use it consistently and do not fall back to the old string-method form.

Export the schema and its inferred type together:

export type RequestType = z.infer<typeof requestSchema>;

Schema Organization

  • API schemas: apps/auth-server/src/app/schemas/ (e.g. auth.ts, oauth.ts, common.ts)
  • Config schemas: libs/server/config/src/lib/schemas/ (env validation)
  • Shared validators: libs/shared/validation/ (email normalization, password strength)

Security and Best Practices

  • Validate all inputs: body, query params, headers, and response shape. Never trust client input.
  • Fail fast: validation happens at the route level via the Fastify schema; invalid requests return 400 before the handler runs.
  • Normalize before validation/use: email normalization (normalizeEmail) happens after format validation but before storage/query.
  • Specific formats: use regex for exact formats (e.g. hex tokens /^[0-9a-fA-F]{64}$/, PKCE verifiers /^[A-Za-z0-9._~-]{43,128}$/).
  • Length limits: set .min() and .max() on strings to prevent DoS (e.g. state: z.string().max(255).optional()).
  • Password strength: use zxcvbn via @qauth-labs/shared-validation; return feedback for weak passwords.

Read the full file on GitHub · 101 lines

Changes

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.

  1. 2d ago First seen · 101 lines · 60 tokens per session scan A 2e12335a9aad

Subscribe to this mod's changes

validation is a skill published in the GitHub repository qauth-labs/qauth (24 stars, last pushed 7d ago), licensed Apache-2.0. It adds 60 tokens to every session and 913 once invoked, about $0.0003 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 2026-08-30.