An authentication setup guide for Next.js 16 applications using Better Auth and ZenStack. It covers configuration, Google, Yandex, and VK ID sign-in, user organisations, one-time email codes, anonymous users, an OAuth provider, and roles.

Use it when editing `lib/auth.ts` or the `Account` and `Session` models, or when `/api/auth/` returns a 500 error without a useful log message.

It gives the agent guidance before changing authentication code or account and session database models. It also helps investigate failed authentication requests, startup schema mismatches, and silent server errors.

better-auth — Skill for Claude Code and Codex by kamiletar/letar

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 kamiletar/letar --skill better-auth

Clone the repo

git clone --depth 1 https://github.com/kamiletar/letar

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/kamiletar/letar/better-auth/github.svg)](https://agentmods.dev/skills/kamiletar/letar/better-auth)

Your own site

<a href="https://agentmods.dev/skills/kamiletar/letar/better-auth"><img src="https://agentmods.dev/badge/skills/kamiletar/letar/better-auth/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/kamiletar/letar/better-auth"><img src="https://agentmods.dev/badge/skills/kamiletar/letar/better-auth.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 118 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,216 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 unknown 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.

Model	Per session	Once invoked
Fable 5.1	$0.00118	$0.01216
Opus 5.5	$0.00047	$0.00486
Sonnet 5.5	$0.00024	$0.00243
Haiku 4.5	$0.00012	$0.00122

Measured yesterday against content hash 6ccff7f28a40, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

better-auth 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 yesterday.

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.

.agents/skills/better-auth/SKILL.md · 97 lines

The source is not reproduced here

A licence we could not identify

The repository carries a LICENSE file, but it is custom or dual enough that GitHub cannot name it and neither can this catalogue. Unknown terms are not permission, so the body is not copied here. Read the licence at the source and decide for yourself.

Read it on GitHub

Files

What ships with it

12 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.

yesterday First seen · 97 lines · 118 tokens per session scan A 6ccff7f28a40

Subscribe to this mod's changes

better-auth is a skill published in the GitHub repository kamiletar/letar (5 stars, last pushed 10d ago), with no licence file. It adds 118 tokens to every session and 1,216 once invoked, about $0.0005 per session on Opus 5.5. 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 2026-11-07.

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better-auth next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
better-authkamiletar/letar	Skill	5	10d ago	none	A	118	Claude Code, Codex
groq-inferencesynthetic-sciences/openscience	Skill	4.4k	yesterday	Apache-2.0	A	77	Claude Code, Codex
igniteui-wc-choose-componentsIgniteUI/igniteui-cli	Skill	137	yesterday	MIT	A	34	Claude Code
bunqueueegeominotti/bunqueue	Skill	591	6d ago	MIT	A	30	Claude Code
spring-boot-4-conventionsloiane/specs-driven-development-spring-angular	Skill	62	yesterday	MIT	A	50	Claude Code
brownfield-onboardingloiane/specs-driven-development-spring-angular	Skill	62	yesterday	MIT	A	47	Claude Code
openapi-contract-firstloiane/specs-driven-development-spring-angular	Skill	62	yesterday	MIT	A	38	Claude Code