A guide to validating and parsing data with Zod, a TypeScript library for checking whether values match defined schemas. It covers schemas, inferred types, parsing, refinements, transforms, and error handling.

Use it to define object schemas, validate strings and other values, choose between parse and safeParse, infer types, compose schemas, and handle validation errors.

It helps catch malformed input and produce predictable validation errors at application boundaries. It also keeps validation rules connected to TypeScript types.

zod — Skill for Claude Code and Codex by MichelKerkmeester

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.

Any agent

npx skills add MichelKerkmeester/skilled-agent-harness_spec-driven-loops --skill zod

Clone the repo

git clone --depth 1 https://github.com/MichelKerkmeester/skilled-agent-harness_spec-driven-loops

Made for: Claude Code, Codex.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/michelkerkmeester/skilled-agent-harness_spec-driven-loops/zod/github.svg)](https://agentmods.dev/skills/michelkerkmeester/skilled-agent-harness_spec-driven-loops/zod)

Your own site

<a href="https://agentmods.dev/skills/michelkerkmeester/skilled-agent-harness_spec-driven-loops/zod"><img src="https://agentmods.dev/badge/skills/michelkerkmeester/skilled-agent-harness_spec-driven-loops/zod/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/michelkerkmeester/skilled-agent-harness_spec-driven-loops/zod"><img src="https://agentmods.dev/badge/skills/michelkerkmeester/skilled-agent-harness_spec-driven-loops/zod.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 71 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,370 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin 100% copy Near-identical to another mod 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.

Model	Per session	Once invoked
Fable 5.1	$0.00071	$0.01370
Opus 5	$0.00036	$0.00685
Sonnet 5	$0.00014	$0.00274
Haiku 4.5	$0.00007	$0.00137

Measured 7d ago against content hash 245fc4ab7341, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

zod 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 7d 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.

Origin

This is a copy

100% identical to zod — 21 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

specs/sk-design/018-sk-design-parent-v2/001-sk-create-chart/008-evilcharts-reference-research/context/evilcharts/.agents/skills/zod/SKILL.md · 128 lines

How it starts

The opening of the file, as written. The whole thing — 128 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Zod Best Practices

Comprehensive schema validation guide for Zod in TypeScript applications. Contains 43 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation.

When to Apply

Reference these guidelines when:

Writing new Zod schemas
Choosing between parse() and safeParse()
Implementing type inference with z.infer
Handling validation errors for user feedback
Composing complex object schemas
Using refinements and transforms
Optimizing bundle size and validation performance
Reviewing Zod code for best practices

Rule Categories by Priority

Priority	Category	Impact	Prefix
1	Schema Definition	CRITICAL	`schema-`
2	Parsing & Validation	CRITICAL	`parse-`
3	Type Inference	HIGH	`type-`
4	Error Handling	HIGH	`error-`
5	Object Schemas	MEDIUM-HIGH	`object-`
6	Schema Composition	MEDIUM	`compose-`
7	Refinements & Transforms	MEDIUM	`refine-`
8	Performance & Bundle	LOW-MEDIUM	`perf-`

Quick Reference

1. Schema Definition (CRITICAL)

schema-use-primitives-correctly - Use correct primitive schemas for each type
schema-use-unknown-not-any - Use z.unknown() instead of z.any() for type safety
schema-avoid-optional-abuse - Avoid overusing optional fields
schema-string-validations - Apply string validations at schema definition
schema-use-enums - Use enums for fixed string values
schema-coercion-for-form-data - Use coercion for form and query data

2. Parsing & Validation (CRITICAL)

parse-use-safeparse - Use safeParse() for user input
parse-async-for-async-refinements - Use parseAsync for async refinements
parse-handle-all-issues - Handle all validation issues not just first
parse-validate-early - Validate at system boundaries
parse-avoid-double-validation - Avoid validating same data twice
parse-never-trust-json - Never trust JSON.parse output

Read the full file on GitHub · 128 lines

Files

What ships with it

48 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.

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.

7d ago First seen · 128 lines · 71 tokens per session scan A 245fc4ab7341

Subscribe to this mod's changes

zod is a skill published in the GitHub repository MichelKerkmeester/skilled-agent-harness_spec-driven-loops (35 stars, last pushed today), licensed MIT. It adds 71 tokens to every session and 1,370 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to zod, differing in 21 lines, and is treated as a copy.

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