competition-browser-persistence

A specialist guide for investigating browser-held state such as cookies, local storage, IndexedDB, cached responses, and service workers, which can affect later web requests and pages.

In plain words
What is it for?
Use it in authorized CTF sandbox investigations to identify the active storage mechanism, connect it to a concrete browser effect, and reproduce the smallest state-dependent path.
Why use it?
It helps explain behavior that is not visible in the page source, including cached authentication, stored sessions, offline responses, or client-side access decisions.

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/zhaoxuya520/reverse-skill/competition-browser-persistence
Any agent
npx skills add zhaoxuya520/reverse-skill --skill competition-browser-persistence
Clone the repo
git clone --depth 1 https://github.com/zhaoxuya520/reverse-skill

Made for: Claude Code, Codex.

Per session 111 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 625 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 $0.00111 $0.00625
Opus 5 $0.00056 $0.00313
Sonnet 5 $0.00022 $0.00125
Haiku 4.5 $0.00011 $0.00063

Measured yesterday against content hash 48282126789e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

competition-browser-persistence 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.

Origin

Copies of this mod

4 near-identical copies found in the catalogue:

CTF-Sandbox-Orchestrator/competition-browser-persistence/SKILL.md · 51 lines

How it starts

The opening of the file, as written. The whole thing — 51 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Competition Browser Persistence

Use this skill only as a downstream specialization after $ctf-sandbox-orchestrator is already active and has established sandbox assumptions, node ownership, and evidence priorities. If that has not happened yet, return to $ctf-sandbox-orchestrator first.

Use this skill when the decisive branch lives in browser-held state rather than only in visible HTML or backend source.

Reply in Simplified Chinese unless the user explicitly requests English.

Quick Start

  1. Identify the active persistence surface first: cookie jar, localStorage, sessionStorage, IndexedDB, Cache Storage, or service worker.
  2. Record origin, scope, domain, path, expiry, and key names before mutating state.
  3. Tie stored state to one concrete effect: request header, rendered branch, cached response, offline behavior, or hidden route access.
  4. Separate boot-time state from runtime-mutated state.
  5. Reproduce the smallest stateful sequence that reaches the decisive branch.

Workflow

1. Map Browser State Surfaces

  • Inspect cookies, storage buckets, service worker registrations, cache entries, and transient globals exposed during boot.
  • Record which origin, host, route, or feature flag each state item actually applies to.
  • Keep auth tokens, refresh material, CSRF state, cached responses, and feature toggles in separate evidence blocks.

2. Tie State To Runtime Behavior

  • Show how stored state becomes request headers, role derivation, route visibility, cached API data, or offline fallback behavior.
  • Compare clean-state and mutated-state runs with one variable changed at a time.
  • Distinguish UI-only state from backend-accepted state.

3. Reduce To The Decisive Persistence Chain

  • Compress the result to the smallest chain: initial page or login -> state persisted -> subsequent request or render branch -> resulting capability.
  • Keep extracted storage, service worker scripts, and replay steps tied to the same origin and route.
  • If the problem broadens into general web routing or worker behavior outside browser persistence, switch back to the broader web-runtime skill.

Read the full file on GitHub · 51 lines

Files

What ships with it

2 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.

  1. yesterday First seen · 51 lines · 111 tokens per session scan A 48282126789e

Subscribe to this mod's changes

competition-browser-persistence is a skill published in the GitHub repository zhaoxuya520/reverse-skill (31,677 stars, last pushed 5d ago), licensed MIT. It adds 111 tokens to every session and 625 once invoked, about $0.0006 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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