visibility

Purpose

Identify functions declared public that are never called internally and remove manual getter functions that duplicate Solidity's auto-generated getters. Both changes reduce unnecessary bytecode and enable downstream optimizations.

public functions generate two ABI dispatch entry points: one for external calls (reads from calldata) and one for internal calls (parameters on stack/memory). external eliminates the internal entry point, enabling calldata for reference parameters.

---

When to Use This Skill

• Writing or reviewing any Solidity function declaration
• Code review of contracts with many public functions
• Pre-audit cleanup of a Foundry-based Solidity project
• After adding new external entry points that do not call internal functions
• After applying VI-001: combine with CD-001 (calldata) for max impact

---

When NOT to Use This Skill

• Functions already declared external — already optimal
• Contracts with no public functions
• Interface-only files or abstract contracts where visibility is inherited
• When only reviewing test files (visibility in tests has no gas impact)
• Functions called internally via bare name (_fn()) or this.fn() — must stay public

---

Platform Detection

Trigger on any .sol file containing public function declarations or manual view getter functions. No tooling prerequisites beyond Read.

# Find public functions
grep -n "public" src/**/*.sol | grep -v "^.*\/\/"

# Find manual getter candidates (view returns single value)
grep -n "view returns" src/**/*.sol

---

Quick Reference

Situation	Action
Function called only externally?	Change to external (VI-001)
Function takes array/struct params AND is external?	Also use calldata (VI-001 + CD-001)
Manual getter for a public state variable?	Remove it (VI-002)
Function called internally (same contract, no this.)?	Must stay public or internal
Function called via this.fn() from inside the contract?	Must stay public
Required by interface (e.g., ERC-20 balanceOf)?	Keep with appropriate visibility

---

Workflow

Step 1 — Find all public functions

• Read the contract and list every function with public visibility
• Exclude constructors, state variable declarations, and interface stubs

Step 2 — Search for internal call sites

• For each public function named fnName: scan the full contract source for bare fnName( calls (without this. prefix) inside other function bodies
• If no internal call sites exist: VI-001 candidate
• Also scan for explicit duplicate getters: view functions whose entire body is return stateVar or return mapping[param] where stateVar/mapping is already public (VI-002 candidate)

Step 3 — Apply changes

• VI-001: Change public to external. For array, struct, bytes, or string parameters, also change memory to calldata (combines VI-001 + CD-001)
• VI-002: Delete the manual getter entirely. Callers use the auto-generated getter
• Run forge test --gas-report to confirm savings; forge test for regressions

---

Output Format

Report each finding using this structure:

**[SEVERITY] Description**
**File:** path/to/Contract.sol, line N
**Technique:** VI-00X
**Estimated saving:** ~X gas per call
[before code block]
[after code block]
**Verification:** rg "fnName\(" --type sol / forge test --gas-report

Concrete example finding

[MEDIUM] batchTransfer is public but never called internally — change to external (VI-001) File: src/NFTMarket.sol, line 24 Technique: VI-001 + CD-001 Estimated saving: ~984 gas per call (array copy + dispatcher overhead)

Before:

function batchTransfer(uint256[] memory ids, address to) public {
    for (uint256 i = 0; i < ids.length; ++i) {
        tokenOwner[ids[i]] = to;
    }
}

After:

function batchTransfer(uint256[] calldata ids, address to) external {
    uint256 len = ids.length;
    for (uint256 i = 0; i < len; ++i) {
        tokenOwner[ids[i]] = to;
    }
}

Verification: rg "batchTransfer\(" --type sol (confirm no internal callers) then forge test --gas-report

---

Supporting Docs

Only read these files when explicitly needed — do not load all three by default:

File	Read only when…
resources/PATTERNS.md	You need VI-001 gas savings for large array parameters (>10 elements) or the VI-002 inheritance edge case
resources/CHECKLIST.md	Producing a formal /decipher-gas-optimizoor:analyze report and confirming all public functions were audited
resources/EXAMPLE_FINDING.md	Generating a report and needing the exact output format for a multi-function NFT contract finding
docs/evm-gas-reference.md	You need calldata byte costs to quantify savings for array/struct parameters