fec-browser-storage

fec-browser-storage is a skill for Claude Code from bovinphang/frontend-craft. It costs 59 tokens per session (431 once invoked), scanned A, original, MIT.

A guide for choosing and implementing browser storage, which lets a website keep data on a user’s device. It covers localStorage, sessionStorage, IndexedDB, cookies, offline data, security, and cleanup.

In plain words
What is it for?
Use it to design or review client-side preferences, temporary tab data, offline caches, authentication cookies, expiration rules, and safe data cleanup.
Why use it?
It helps prevent unsuitable storage choices, such as putting sensitive tokens where JavaScript can read them or blocking the page with large synchronous writes.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin.

Part of the frontend-craft plugin — 56 skills, 11 commands, 14 agents, 5 hooks, 6 MCP servers shipped together

Good fit Use it to design or review client-side preferences, temporary tab data, offline caches, authentication cookies, expiration rules, and safe data cleanup.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/bovinphang/frontend-craft/fec-browser-storage
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 bovinphang/frontend-craft --skill fec-browser-storage
Clone the repo
git clone --depth 1 https://github.com/bovinphang/frontend-craft

Made for: Claude Code.

Or install frontend-craft, the plugin that ships this one along with the rest of its 56 skills, 11 commands, 14 agents, 5 hooks, 6 MCP servers.

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.

agentmods badge for fec-browser-storage

README.md
[![agentmods](https://agentmods.dev/badge/skills/bovinphang/frontend-craft/fec-browser-storage/github.svg)](https://agentmods.dev/skills/bovinphang/frontend-craft/fec-browser-storage)
Your own site
<a href="https://agentmods.dev/skills/bovinphang/frontend-craft/fec-browser-storage"><img src="https://agentmods.dev/badge/skills/bovinphang/frontend-craft/fec-browser-storage/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.

agentmods 80×15 button for fec-browser-storage

Your own site · 80×15
<a href="https://agentmods.dev/skills/bovinphang/frontend-craft/fec-browser-storage"><img src="https://agentmods.dev/badge/skills/bovinphang/frontend-craft/fec-browser-storage.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 59 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 431 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 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 5.1 $0.00059 $0.00431
Opus 5 $0.00030 $0.00216
Sonnet 5 $0.00012 $0.00086
Haiku 4.5 $0.00006 $0.00043

Measured 9d ago against content hash 01f7f7b71c02, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

fec-browser-storage 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 9d 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.

localized/zh-CN/skills/fec-browser-storage/SKILL.md · 35 lines

What it actually says

浏览器存储

用途

根据数据大小、安全要求和生命周期选择合适的客户端存储方案。

流程

  1. 先判断数据敏感度、体积、生命周期、是否需要跨 Tab、是否需要随请求发送。
  2. 小量非敏感偏好用 localStorage;Tab 级临时数据用 sessionStorage;大量结构化数据或离线缓存用 IndexedDB;认证态优先 httpOnly cookie。
  3. 封装统一 key 前缀、JSON parse/stringify、异常处理、过期清理和 quota 兜底。
  4. 敏感数据按安全规则处理,不把明文 token、密码、信用卡信息放进可被 JS 读取的存储。
  5. 审查隐私模式、存储配额、清理策略和跨浏览器兼容性。

详细参考

涉及存储选型表、localStorage/sessionStorage 封装、IndexedDB 示例、Cookie 辅助方法和敏感数据规则时,加载 references/storage-patterns.md

约束

  • localStorage/sessionStorage 是同步 API,大数据读写会阻塞主线程。
  • 除 httpOnly cookie 外,客户端存储都可被 XSS 读取。
  • Cookie 每次请求自动携带,不适合大数据。
  • IndexedDB 配额和隐私模式行为有浏览器差异。
  • URL 中不要传 token 或敏感数据。

预期输出

产出统一的 storage/cookie/db 封装,key 有命名空间,数据有过期或清理策略,敏感数据只进入合适的安全边界。

Files

What ships with it

1 file 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.

  1. 9d ago First seen · 35 lines · 59 tokens per session scan A 01f7f7b71c02

Subscribe to this mod's changes

fec-browser-storage is a skill published in the GitHub repository bovinphang/frontend-craft (21 stars, last pushed 8d ago), licensed MIT. It adds 59 tokens to every session and 431 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.

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