storage-layout-safety

storage-layout-safety is a skill for Claude Code, Codex from PlamenTSV/plamen. It costs 20 tokens per session (2,598 once invoked), scanned A, original, MIT.

A review of how an EVM smart contract stores persistent data. EVM is the execution system used by Ethereum and compatible blockchains, where storage is organized into numbered 256-bit slots.

In plain words
What is it for?
Use it when reviewing contracts with proxies, upgrades, low-level assembly, delegate calls, or manual storage slots.
Why use it?
It looks for storage mistakes that can overwrite data, lose updates, or break proxy and upgradeable contracts.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it when reviewing contracts with proxies, upgrades, low-level assembly, delegate calls, or manual storage slots.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/plamentsv/plamen/storage-layout-safety
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 PlamenTSV/plamen --skill storage-layout-safety
Clone the repo
git clone --depth 1 https://github.com/PlamenTSV/plamen

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.

agentmods badge for storage-layout-safety

README.md
[![agentmods](https://agentmods.dev/badge/skills/plamentsv/plamen/storage-layout-safety.svg)](https://agentmods.dev/skills/plamentsv/plamen/storage-layout-safety)
Your own site
<a href="https://agentmods.dev/skills/plamentsv/plamen/storage-layout-safety"><img src="https://agentmods.dev/badge/skills/plamentsv/plamen/storage-layout-safety.svg" alt="Measured on agentmods" height="20"></a>
Per session 20 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,598 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. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 1 finding, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high Anti-Refusal · line 168
    Skill instructs the agent to never refuse or to always comply. Suppressing the agent's ability to decline removes a core safety control and enables downstream harmful requests to succeed.
    Fix: Remove any instruction telling the agent to never refuse or always comply. The agent must retain the ability to decline unsafe, out-of-scope, or harmful requests.
How audits are shown
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 $0.00020 $0.02598
Opus 5 $0.00010 $0.01299
Sonnet 5 $0.00004 $0.00520
Haiku 4.5 $0.00002 $0.00260

Measured 8d ago against content hash 250a4b8bab87, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

storage-layout-safety 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 8d 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.

agents/skills/evm/storage-layout-safety/SKILL.md · 191 lines

How it starts

The opening of the file, as written. The whole thing — 191 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Skill: Storage Layout Safety

Type: Thought-template (instantiate before use) Trigger Pattern: STORAGE_LAYOUT flag detected Inject Into: depth-state-trace, depth-edge-case Finding prefix: [SLS-N] Rules referenced: R1, R4, R8, R10, R14

Covers: memory vs storage confusion, lost writes, proxy/upgrade storage collisions, inline assembly slot safety, and storage semantic corruption.

This vulnerability class exists ONLY on EVM - type-safe VMs (Move, Solana's Borsh model) enforce layout correctness at the runtime level. EVM's untyped 256-bit slot model permits silent corruption when layouts diverge.


Trigger Patterns

proxy|upgradeable|diamond|delegatecall|EIP1967|StorageSlot|
sstore|sload|assembly\s*\{|tstore|tload|reinitializer|
UUPSUpgradeable|TransparentUpgradeableProxy|BeaconProxy

Step 1: Storage Surface Inventory

Map the contract's persistent state surface before analyzing bugs:

# Variable Type Slot Assignment Written By Read By Proxy-Relevant?

For each state variable, determine:

  • Sequential layout (compiler-assigned) vs manual slot (EIP-1967, custom bytes32 constant)?
  • Accessed via Solidity or via assembly sstore/sload?
  • For structs: trace slot computation (base + offset). For mappings: keccak256(key . slot). For arrays: keccak256(slot) + index.

Tag: [TRACE:variable={name} → slot={computation} → writers={functions}]


Step 2: Memory vs Storage Confusion

For each function operating on structs or complex types:

2a. Reference Type Assignment

Trace every local variable of struct, array, or mapping type:

  • Declared as storage or memory?
  • If memory: is the function INTENDING to modify persistent state? If yes → lost write (copy modified in memory, never persisted).
  • If storage: does every code path that modifies the reference complete without early return before the write?

2b. Parameter Data Location

For each function accepting struct/array parameters:

  • Is the parameter memory or calldata?
  • Does the function modify the parameter expecting persistence? function update(MyStruct memory s) modifies s.field but s is a memory copy - original unchanged.

Read the full file on GitHub · 191 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. 8d ago First seen · 191 lines · 20 tokens per session scan A 250a4b8bab87

Subscribe to this mod's changes

storage-layout-safety is a skill published in the GitHub repository PlamenTSV/plamen (286 stars, last pushed yesterday), licensed MIT. It adds 20 tokens to every session and 2,598 once invoked, about $0.0001 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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