GateGuard — Fact-Forcing Pre-Action Gate

A PreToolUse hook that forces Claude to investigate before editing. Instead of self-evaluation ("are you sure?"), it demands concrete facts. The act of investigation creates awareness that self-evaluation never did.

When to Activate

• Working on any codebase where file edits affect multiple modules
• Projects with data files that have specific schemas or date formats
• Teams where AI-generated code must match existing patterns
• Any workflow where Claude tends to guess instead of investigating

Core Concept

LLM self-evaluation doesn't work. Ask "did you violate any policies?" and the answer is always "no." This is verified experimentally.

But asking "list every file that imports this module" forces the LLM to run Grep and Read. The investigation itself creates context that changes the output.

Three-stage gate:

1. DENY  — block the first Edit/Write/Bash attempt
2. FORCE — tell the model exactly which facts to gather
3. ALLOW — permit retry after facts are presented

No competitor does all three. Most stop at deny.

Evidence

Two independent A/B tests, identical agents, same task:

Both agents produce code that runs and passes tests. The difference is design depth.

Gate Types

Edit / MultiEdit Gate (first edit per file)

MultiEdit is handled identically — each file in the batch is gated individually; entries without their own file_path are gated as the call's file_path. NotebookEdit is gated as an Edit of its notebook_path: same class, checked key, credit and cap rules, the full questions (the cell change is not read), and never a comment-only pass.

The questions depend on the target's class (see Questions by target class). For code targets the Edit gate asks:

Before editing {file_path}, present these facts:

1. List ALL files that import/require this file (search the tree — Glob/Grep, or find/grep via Bash)
2. List the public functions/classes affected by this change
3. If this file reads/writes data files, show field names, structure,
   and date format (use redacted or synthetic values, not raw production data)
4. Quote the user's current instruction verbatim

These four are the full set, asked whenever the change cannot be read with confidence. When it can (see Questions fit the change), an edit that touches no public declaration asks instead for the call sites in the file or its module that rely on the changed behaviour, and item 3 is dropped when the change handles no data.

Write Gate (first new file creation)

For code targets the Write gate asks:

Before creating {file_path}, present these facts:

1. Name the file(s) and line(s) that will call this new file
2. Confirm no existing file serves the same purpose (search the tree — Glob/Grep, or find/grep via Bash)
3. If this file reads/writes data files, show field names, structure,
   and date format (use redacted or synthetic values, not raw production data)
4. Quote the user's current instruction verbatim

Item 3 is dropped when the new content handles no data.

Questions fit the change

For code targets the gate reads the change it is about to allow (Edit old_string/new_string, every MultiEdit entry for the file, Write content) and decides three things:

• Public surface: a line on either side declares or exposes a public name. JS/TS: export, exports, public, declare (.d.ts files always); Python: def/class not starting with _, dunders, __all__, a module-level public assignment such as BASE_URL = ... (__init__.py always); Go: capitalised func/type/var/const names, package, lines starting with a capital; Rust: pub, impl, trait, extern, #[macro_export], #[derive], #[repr], #[no_mangle]; shell: function definitions, export, declare -x; PowerShell: function, filter, param, Export-ModuleMember, [CmdletBinding. A member of an exported container counts too, judged from the file: lines inside an exported interface, enum, type, object or export list, member declarations of an exported class, __all__ entries, public class attributes and dataclass fields, and members

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