New Config
lidofinance/diffyscan
Creates or extends a Diffyscan verification config for a deployed contract or deployment.
Create Foundry differential tests comparing production Solidity contracts against an independent reference model.
Install Foundry Differential Tests
$ npx skills add aviggiano/security --skill foundry-differential-tests -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install aviggiano/security foundry-differential-tests --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/aviggiano/security.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/foundry-differential-tests .claude/skills/foundry-differential-tests && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "foundry-differential-tests" agent skill from https://github.com/aviggiano/security/tree/main/skills/foundry-differential-tests into .claude/skills/foundry-differential-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "foundry-differential-tests", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/aviggiano/security/tree/main/skills/foundry-differential-testsType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add aviggiano/security --skill foundry-differential-tests -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install aviggiano/security foundry-differential-tests --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/aviggiano/security.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/foundry-differential-tests .agents/skills/foundry-differential-tests && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "foundry-differential-tests" agent skill from https://github.com/aviggiano/security/tree/main/skills/foundry-differential-tests into .agents/skills/foundry-differential-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "foundry-differential-tests", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add aviggiano/security --skill foundry-differential-tests -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install aviggiano/security foundry-differential-tests --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/aviggiano/security.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/foundry-differential-tests .cursor/skills/foundry-differential-tests && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "foundry-differential-tests" agent skill from https://github.com/aviggiano/security/tree/main/skills/foundry-differential-tests into .cursor/skills/foundry-differential-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "foundry-differential-tests", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/aviggiano/security.git --path skills/foundry-differential-tests--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add aviggiano/security --skill foundry-differential-tests -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install aviggiano/security foundry-differential-tests --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/aviggiano/security.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/foundry-differential-tests .gemini/skills/foundry-differential-tests && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "foundry-differential-tests" agent skill from https://github.com/aviggiano/security/tree/main/skills/foundry-differential-tests into .gemini/skills/foundry-differential-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "foundry-differential-tests", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install aviggiano/security foundry-differential-testsInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add aviggiano/security --skill foundry-differential-tests -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/aviggiano/security.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/foundry-differential-tests .github/skills/foundry-differential-tests && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "foundry-differential-tests" agent skill from https://github.com/aviggiano/security/tree/main/skills/foundry-differential-tests into .github/skills/foundry-differential-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "foundry-differential-tests", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add aviggiano/security --skill foundry-differential-tests -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install aviggiano/security foundry-differential-tests --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/aviggiano/security.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/foundry-differential-tests .opencode/skills/foundry-differential-tests && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "foundry-differential-tests" agent skill from https://github.com/aviggiano/security/tree/main/skills/foundry-differential-tests into .opencode/skills/foundry-differential-tests/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "foundry-differential-tests", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
foundry-differential-tests- GitHub stars
- 144
- Token cost
- ~613 tokens
- SKILL.md length
- 275 words
- Files
- 2
- Skills in repo
- 10
- Repo updated
- First seen
- Licence
- MIT
At a glance
Create Foundry differential tests comparing production Solidity contracts against an independent reference model.
- Works in 5 steps: Start with deterministic scenarios that… → Execute the same operation on production… → Compare all relevant public state after… → …
- Codex needs paired deployments
- SKILL.md covers Setup, Test Construction, Equality And Tolerance and Failure Handling, plus 1 more section
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
What it does
Foundry Differential Tests is an agent skill from aviggiano/security. Create Foundry differential tests comparing production Solidity contracts against an independent reference model. Use when Codex needs paired deployments, paired actions, public-view state comparisons, strict equality checks, and root-cause classification of production/reference divergence.
Its SKILL.md is about 610 tokens, which your agent loads only when the skill is triggered. The skill folder holds 2 other files (for example `agents/openai.yaml`).
It sits in Backend & APIs, covering Deployment, Smart contracts and Root cause analysis. It works with Solidity. The repository describes itself as: Security Reviews and Audit Checklists. The licence is MIT.
When your agent uses it
- Codex needs paired deployments
- Public-view state comparisons
- Strict equality checks
- Root-cause classification of production/reference divergence
Example prompts
- “/foundry-differential-tests”
Workflow steps
5 steps, taken from the first numbered list in SKILL.md.
- Start with deterministic scenarios that each prove one public semantic.
- Execute the same operation on production and reference.
- Compare all relevant public state after each step.
- Add fuzzing only after deterministic coverage has pinned the behavior.
- Keep helpers symmetric: _placeLimitPair, _marketOrderPair, _batchPair, _assert...Pair.
What it can do on your machine
Read from SKILL.md and the folder at commit e18ce7d. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md.
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
Foundry Differential Tests loads about 613 tokens when it runs. Until then it costs about 80 tokens; SKILL.md has 275 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from aviggiano/security at commit e18ce7d, republished under its MIT licence (© aviggiano). 275 words, ~613 tokens.
Download SKILL.mdSave it as
.claude/skills/foundry-differential-tests/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.- name
- foundry-differential-tests
- description
- Create Foundry differential tests comparing production Solidity contracts against an independent reference model. Use when Codex needs paired deployments, paired actions, public-view state comparisons, strict equality checks, and root-cause classification of production/reference divergence.
Foundry Differential Tests
Setup
Deploy production and reference systems side by side. Use shared actor setup, balances, markets, approvals, and configuration. Keep the paired-action helpers in a differential base contract.
Compare public behavior, not internals:
- return values
- ERC20/native balances
- deposited/locked/available balances from view functions
- public order/market/price-level views
- public metadata and configuration views
Do not compare internal storage layout, packed ids, or implementation-private traversal state unless the public interface exposes it.
Test Construction
- Start with deterministic scenarios that each prove one public semantic.
- Execute the same operation on production and reference.
- Compare all relevant public state after each step.
- Add fuzzing only after deterministic coverage has pinned the behavior.
- Keep helpers symmetric:
_placeLimitPair,_marketOrderPair,_batchPair,_assert...Pair.
Use typed interfaces for the reference boundary. Raw fallback calldata should only be modeled if the task explicitly includes fallback ABI behavior.
Equality And Tolerance
Default to strict equality. A one-unit mismatch is still a finding. Add tolerance only when the public spec defines tolerance or the user explicitly asks for an approximate property.
Failure Handling
When a differential test fails, classify before fixing:
harness defect: the paired setup is invalid or asymmetricreference bug: the independent model does not match public/spec behaviorproduction bug: production diverges from public/spec behaviorspec mismatch: the test documents a behavior not satisfied by production and should intentionally remain failing
Fix harness defects and reference bugs when requested. Preserve production/spec failures unless the user explicitly asks to change production code.
Validation
Run focused tests first, then the differential suite. If the fixture has a reference-only switch, also run representative tests against the reference-only deployment to catch reference completeness gaps.
© aviggiano, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
SKILL.md and 1 other file in skills/foundry-differential-tests of aviggiano/security.
- SKILL.md
- agents/openai.yaml
Open the folder on GitHubat commit e18ce7d
Compare with similar skills
Foundry Differential Tests next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Foundry Differential Tests this skillaviggiano/security | 144 | — | ~613 | Automated safety check: Pass | MIT | |
| New Configlidofinance/diffyscan | 142 | — | ~1k | Automated safety check: Pass | MIT | |
| Validate Configlidofinance/diffyscan | 142 | — | ~1.1k | Automated safety check: Pass | MIT | |
| function Object() { [native code] } Patternsccashwell/evm-cortex | 131 | — | ~1.7k | Automated safety check: Pass | MIT | |
| Cross Chain Securityccashwell/evm-cortex | 131 | — | ~1.7k | Automated safety check: Pass | MIT | |
| Test Fixturesccashwell/evm-cortex | 131 | — | ~1.9k | Automated safety check: Pass | MIT |
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Constructor and initializer patterns for deploying Solidity contracts.
Cross Chain Security
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Cross-chain security patterns for multi-chain Solidity deployments and bridge interactions.
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A skill your agent uses when setting up test environments for Solidity protocols.
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Related
Works with
Categories
Questions about Foundry Differential Tests
What does Foundry Differential Tests do?
Create Foundry differential tests comparing production Solidity contracts against an independent reference model. Foundry Differential Tests is an agent skill from aviggiano/security. Create Foundry differential tests comparing production Solidity contracts against an independent reference model.
When should I use Foundry Differential Tests?
Foundry Differential Tests fits situations like: Codex needs paired deployments; public-view state comparisons; strict equality checks; root-cause classification of production/reference divergence.
How do I install Foundry Differential Tests in Claude Code?
Run `npx skills add aviggiano/security --skill foundry-differential-tests -a claude-code`. Or copy the skill folder (skills/foundry-differential-tests in aviggiano/security) into .claude/skills/foundry-differential-tests in your project. Claude Code loads it when a task matches its description.
How do I install Foundry Differential Tests in Codex?
Run `npx skills add aviggiano/security --skill foundry-differential-tests -a codex`. Or copy the skill folder (skills/foundry-differential-tests in aviggiano/security) into .agents/skills/foundry-differential-tests in your project. Codex loads it when a task matches its description.
Can I use Foundry Differential Tests in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add aviggiano/security --skill foundry-differential-tests -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/foundry-differential-tests, .gemini/skills/foundry-differential-tests, .github/skills/foundry-differential-tests and .opencode/skills/foundry-differential-tests in your project.
What does Foundry Differential Tests need to run?
SKILL.md names no scripts, command-line tools or credentials: Foundry Differential Tests is instructions for the agent only.
Does Foundry Differential Tests access the network?
SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.
Is Foundry Differential Tests safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does Foundry Differential Tests use?
Foundry Differential Tests is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Foundry Differential Tests use?
About 613 tokens (SKILL.md is roughly 2.5k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.
What are the alternatives to Foundry Differential Tests?
Skills that share tags, products or a category with Foundry Differential Tests: New Config (lidofinance/diffyscan, 142 stars), Validate Config (lidofinance/diffyscan, 142 stars), function Object() { [native code] } Patterns (ccashwell/evm-cortex, 131 stars) and Cross Chain Security (ccashwell/evm-cortex, 131 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Foundry Differential Tests?
aviggiano (a GitHub user) maintains it in aviggiano/security, which has 144 GitHub stars. The repository holds 10 skills in this directory. The repository was last updated on September 15, 2026.
Source: aviggiano/security on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.