check-cache-bugs

check-cache-bugs is a command for Claude Code from FlorianBruniaux/claude-code-plugins. It costs 39 tokens per session (3,860 once invoked), scanned A, original, MIT.

A command that checks a Claude Code installation for known cache, session-resume, configuration, and attribution problems.

In plain words
What is it for?
Use it to audit Claude Code versions, configuration files, project instructions, skills, hooks, shell profiles, and installed Claude binaries.
Why use it?
It helps identify whether the installed version or local setup is affected by documented bugs before they cause confusing results or extra costs.

Command for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: reads .claude/ paths; mentions CLAUDE.md; mentions subagents.

Part of the session-tools plugin — 8 skills, 6 commands, 1 agent, 1 plugin shipped together

Good fit Use it to audit Claude Code versions, configuration files, project instructions, skills, hooks, shell profiles, and installed Claude binaries.

Compare 6 commands from other repositories ↓
Install with agentmods
npx agentmods add commands/florianbruniaux/claude-code-plugins/check-cache-bugs
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.

Clone the repo
git clone --depth 1 https://github.com/FlorianBruniaux/claude-code-plugins

Made for: Claude Code.

Or install session-tools, the plugin that ships this one along with the rest of its 8 skills, 6 commands, 1 agent, 1 plugin.

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 check-cache-bugs

README.md
[![agentmods](https://agentmods.dev/badge/commands/florianbruniaux/claude-code-plugins/check-cache-bugs/github.svg)](https://agentmods.dev/commands/florianbruniaux/claude-code-plugins/check-cache-bugs)
Your own site
<a href="https://agentmods.dev/commands/florianbruniaux/claude-code-plugins/check-cache-bugs"><img src="https://agentmods.dev/badge/commands/florianbruniaux/claude-code-plugins/check-cache-bugs/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 check-cache-bugs

Your own site · 80×15
<a href="https://agentmods.dev/commands/florianbruniaux/claude-code-plugins/check-cache-bugs"><img src="https://agentmods.dev/badge/commands/florianbruniaux/claude-code-plugins/check-cache-bugs.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 39 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 3,860 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. 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 $0.00039 $0.03860
Opus 5.5 $0.00016 $0.01544
Sonnet 5.5 $0.00008 $0.00772
Haiku 4.5 $0.00004 $0.00386

Measured 1mo ago against content hash da7e358d56a5, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

check-cache-bugs scanned grade A with 1 finding 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 1mo 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.

Reads agent configuration directorieslowAgent snooping

.claude/, .codex/, .gemini/ hold keys, settings and other credentials a mod has no legitimate need for.

grep -rl "cch=" ~/.claude/hooks/ 2>/dev/null

Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.

plugins/session-tools/commands/check-cache-bugs.md · 312 lines

How it starts

The opening of the file, as written. The whole thing — 312 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Check Cache Bugs (CC#40524)

Audit your Claude Code setup for cache and cost bugs discovered in March–April 2026.

Time: ~30 seconds | Scope: version, config files, CLAUDE.md, skills, hooks, shell profiles, all claude binaries

Note on cache contamination: This skill loads content containing cch= strings into the current session's message array. For cleanest results, run this command at the very start of a fresh session — or via claude -p "$(cat .claude/commands/check-cache-bugs.md)" as a one-shot print-mode invocation.

Reference: anthropics/claude-code#40524 | Discovered by: @jmarianski + @whiletrue0x | Extended by: @ArkNill (ArkNill/claude-code-cache-analysis, April 2026)


Background

Fix Status (current as of v2.1.92)

Bug Versions affected Status
Bug 1 — cch sentinel (standalone binary) v2.1.36–v2.1.90 FIXED in v2.1.91
Bug 2 — deferred_tools_delta on --resume v2.1.69–v2.1.89 FIXED in v2.1.90
Bug 3 — attribution header per-session hash v2.1.69+ Active (env var workaround)
B4 — Microcompact / silent context stripping all versions through v2.1.92 Active (GrowthBook controlled)
B5 — Tool result budget cap 200K all versions through v2.1.92 Active (MCP tools exempted)

Original three bugs (CC#40524)

  • Bug 1 (FIXED v2.1.91): Bun's native HTTP layer did a same-length byte replacement of the cch=00000 attestation placeholder after JSON.stringify but before TLS. Triggered only if cch=00000 appeared literally in messages[] content. Confirmed closed — npm and standalone binary are now equivalent on v2.1.91+.

  • Bug 2 (FIXED v2.1.90): The session JSONL writer stripped deferred_tools_delta attachment records before writing to disk. On --resume, those records were absent — the deferred tools layer had no prior history and re-announced all tools from scratch, shifting every message position and breaking the messages-level cache prefix entirely. Each resume rebuilt 87-118K tokens as cache_creation. Anthropic tracked internally as inc-4747.

Read the full file on GitHub · 312 lines

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. 1mo ago First seen · 312 lines · 39 tokens per session scan A da7e358d56a5

Subscribe to this mod's changes

check-cache-bugs is a command published in the GitHub repository FlorianBruniaux/claude-code-plugins (42 stars, last pushed 1mo ago), licensed MIT. It adds 39 tokens to every session and 3,860 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 1 finding (reads agent configuration directories). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-04.