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Agent skill

Arktype

by EpicenterHQ in EpicenterHQ/epicenter

Arktype: runtime validation, discriminated unions with .merge()/.or(), spread keys.

Custom licenceAuto-check passed

Install Arktype

skills CLI
$ npx skills add EpicenterHQ/epicenter --skill arktype -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install EpicenterHQ/epicenter arktype --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/EpicenterHQ/epicenter.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/arktype .claude/skills/arktype && rm -rf skills-src

Use ~/.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/

Facts

Skill name
arktype
GitHub stars
4.8k
Token cost
~3.3k tokens
SKILL.md length
989 words
Files
1
Skills in repo
65
Repo updated
First seen
Licence
Custom licence

At a glance

Arktype: runtime validation, discriminated unions with .merge()/.or(), spread keys.

  • Works in 5 steps: type.or(...) creates a union of plain… → commandBase.merge(union) distributes the… → The result is a union where each branch… → …
  • Mentioning arktype
  • SKILL.md covers base.merge(type.or(...))…, .merge().or() Chaining Pattern…, The "..." Spread Key Pattern… and .or() Chaining vs type.or()…, plus 10 more sections
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Arktype is an agent skill from EpicenterHQ/epicenter. Arktype: runtime validation, discriminated unions with .merge()/.or(), spread keys. Use when mentioning arktype, type(), union types, command/event schemas.

Its SKILL.md is about 3.3k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

The repository describes itself as: Open-source, local-first apps.

When your agent uses it

  • Mentioning arktype
  • Command/event schemas

Example prompts

  • “/arktype”

Workflow steps

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

  1. type.or(...) creates a union of plain object definitions. Each is a variant with its own fields.
  2. commandBase.merge(union) distributes the merge across each branch of the union. Internally, arktype calls rNode.distribute() to apply the…
  3. The result is a union where each branch has all commandBase fields plus its variant-specific fields.
  4. Arktype auto-detects the action key as a discriminant because each branch has a distinct literal value.
  5. switch (cmd.action) in TypeScript narrows the full union. Payload fields and result types are type-safe per branch.

What it can do on your machine

Read from SKILL.md and the folder at commit 9cc65c3. 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 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

    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

Arktype loads about 3.3k tokens when it runs. Until then it costs about 41 tokens; SKILL.md has 989 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~41
When it runs · the whole SKILL.md, loaded when a task matches
~3.3k

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

Its licence (Custom licence) doesn't allow us to republish the file, so here is its outline and opening line. It has 989 words (~3,270 tokens).

“Patterns for composing arktype schemas, naming runtime schema values alongside inferred types, and building discriminated unions with .merge() and .or().”

— opening of SKILL.md by EpicenterHQ, Custom licence
name
arktype
metadata.author
epicenter
metadata.version
1.0

Read the full SKILL.md on GitHub

Files

Just SKILL.md in .agents/skills/arktype of EpicenterHQ/epicenter.

Open the folder on GitHubat commit 9cc65c3

Compare with similar skills

Arktype 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.

Arktype compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Arktype this skillEpicenterHQ/epicenter4.8k—~3.3kAutomated safety check: PassCustom licence
Mergeremotion-dev/remotion62k—~508Automated safety check: PassCustom licence
Mergewithastro/astro63k—~153Automated safety check: PassCustom licence
Merge Upsymfony/symfony31k—~4kAutomated safety check: PassMIT
Mergealirezarezvani/claude-skills28k1 repos~587Automated safety check: PassMIT
Merging PRsPostHog/posthog40k—~4.1kAutomated safety check: PassCustom licence

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Questions about Arktype

What does Arktype do?

Arktype: runtime validation, discriminated unions with .merge()/.or(), spread keys. Arktype is an agent skill from EpicenterHQ/epicenter.or(), spread keys.

When should I use Arktype?

Arktype fits situations like: mentioning arktype; command/event schemas.

How do I install Arktype in Claude Code?

Run `npx skills add EpicenterHQ/epicenter --skill arktype -a claude-code`. Or copy the skill folder (.agents/skills/arktype in EpicenterHQ/epicenter) into .claude/skills/arktype in your project. Claude Code loads it when a task matches its description.

How do I install Arktype in Codex?

Run `npx skills add EpicenterHQ/epicenter --skill arktype -a codex`. Or copy the skill folder (.agents/skills/arktype in EpicenterHQ/epicenter) into .agents/skills/arktype in your project. Codex loads it when a task matches its description.

Can I use Arktype 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 EpicenterHQ/epicenter --skill arktype -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/arktype, .gemini/skills/arktype, .github/skills/arktype and .opencode/skills/arktype in your project.

What does Arktype need to run?

SKILL.md names no scripts, command-line tools or credentials: Arktype is instructions for the agent only.

Does Arktype access the network?

SKILL.md names 1 domain. As links in the text: github.com. This is read from the text; nothing was executed.

Is Arktype 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 Arktype use?

Arktype has a licence file (the repository's licence) that doesn't match a standard licence. Read it on GitHub before reusing the skill.

How many tokens does Arktype use?

About 3.3k tokens (SKILL.md is roughly 13k 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 Arktype?

Skills that share tags, products or a category with Arktype: Merge (remotion-dev/remotion, 62k stars), Merge (withastro/astro, 63k stars), Merge Up (symfony/symfony, 31k stars) and Merge (alirezarezvani/claude-skills, 28k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Arktype?

EpicenterHQ (a GitHub organization) maintains it in EpicenterHQ/epicenter, which has 4,819 GitHub stars. The repository holds 65 skills in this directory. The repository was last updated on October 8, 2026.

Source: EpicenterHQ/epicenter on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.