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:

Task	Gated	Ungated	Gap
Analytics module	8.0/10	6.5/10	+1.5
Webhook validator	10.0/10	7.0/10	+3.0
Average	9.0	6.75	+2.25

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 of a pub enum, struct, trait or use list. Java, Kotlin, C#, C, C++ and batch files, and every Write, always count as touching it. Touching it keeps questions 1 and 2; otherwise both are replaced by "List the call sites in this file or its module that rely on the changed behaviour".
• Data: words for file I/O, formats (json, csv, yaml, …), serialisation, encodings, schemas, SQL, data stores, browser storage, dates and clock reads on either side; in shell scripts also redirection to a file, curl, wget, jq and PowerShell file and web cmdlets. Without them the data question is dropped. With GATEGUARD_EXTERNAL_CONTRACT_QUESTION on, a change that keeps the data question is also asked what outside the repository decides its format or semantics.
• Trivial: see Comment and whitespace-only edits.

Supported extensions: .js .mjs .cjs .jsx .ts .tsx .mts .cts .py .pyi .go .rs .java .kt .kts .cs .c .h .cc .cpp .cxx .hpp .hh .hxx .sh .bash .zsh .ps1 .psm1 .bat .cmd. Any other extension, a missing or non-string field, more than 64 MultiEdit entries, a side over 64 KiB, or 256 KiB in total means the full questions, word for word: the original four (importers, public API, data schemas, the user's instruction), or five with GATEGUARD_EXTERNAL_CONTRACT_QUESTION on. Sensitive and hard-linked targets and NotebookEdit calls always get the full questions. Other classes keep their class questions. Each question has a stable id (importers, public-api, local-callers, callers, no-duplicate, data-schema, external-contract when opted in, quote-instruction, and one per class question), listed in docs/gateguard/change-profile.md.

Questions by target class

The code questions carry no signal for a SKILL.md, a README, a test, or a YAML file, so the first-touch gate classifies the target first.

Classification uses the target's path relative to the project root (CLAUDE_PROJECT_DIR, then the payload cwd, then the process directory), so a project that lives under, say, ~/work/tests/ does not turn every file into a test. A leading .claude/worktrees/<name>/ is stripped, since a worktree mirrors the project, but only when <root>/.claude/worktrees/<name>/.git exists; otherwise the path stays under .claude. On Windows-style paths (and any segment containing ::$), trailing dots/spaces and a :stream suffix are dropped first, so CLAUDE.md. and CLAUDE.md::$DATA classify as CLAUDE.md. Targets outside the root are classified by their absolute path. The path is lowercased and /-separated, and the first match wins:

1. instruction — basename CLAUDE.md, AGENTS.md, AGENT.md, GEMINI.md, SKILL.md, copilot-instructions.md, .cursorrules, or .windsurfrules; any .mdc file; a .md/.mdx/.txt file under a .claude, agents, commands, skills, rules, hooks, .cursor, .codex, or .opencode directory; or a *instructions*.md file under .github/
2. test — *.test.*, *.spec.*, test_*.py, *_test.py, *_test.go, or anything under a tests, test, or __tests__ directory
3. prose — .md, .mdx, .txt, .rst, .adoc
4. config — .json, .jsonc, .yaml, .yml, .toml, .ini, or a .env / .env.* file that does not end in a code extension (.env.local is config; .env.example.ts and .envrc are code)
5. code — everything else (a .js under hooks/ or skills/ is code)

Every class ends with "Quote the user's current instruction verbatim", keeps the batch-sibling warning, and uses the same questions for Edit, MultiEdit, and Write unless noted. Items marked (search) carry the suffix "(search the tree — Glob/Grep, or find/grep via Bash)".

Class	Questions
instruction	Name the harness/loader that reads this file (Claude Code, Codex, Cursor, OpenCode, …) and when it loads it · Describe what agent behaviour changes as a result · Confirm no existing instruction, skill, or agent file already covers this (search)
test	Name what behaviour is under test and which module/function it exercises · Name the existing test file(s) covering this module, or confirm none exist (search)
prose (Write)	Name any existing doc this supersedes or duplicates (search) · State where it will be linked or referenced from · Explain why a new file rather than editing an existing one
prose (Edit)	List other docs or code that reference the section being changed (search) · State what the change corrects or adds
config	Name which process/tool reads this file and when · Describe the effect of the change · Confirm no secrets or credentials are being written in plain text

Condensed denials (after GATEGUARD_FACT_FORCE_FULL_DENIALS) carry a one-line hint for the same class. For code targets the hint names the same questions as the full denial, one short phrase each; an Edit whose change cannot be read keeps the fixed hint (importers/callers, affected API, data schemas if any) when the external-contract question is off. Opting in adds its external-contract phrase. Besides the message text, the class only decides sibling collapse: which files may collapse, and that a sibling must share the first file's class.

Destructive Bash Gate (every destructive command)

Triggers on: rm -rf, git reset --hard, git push --force, drop table, etc.

1. List all files/data this command will modify or delete
2. Write a one-line rollback procedure
3. Quote the user's current instruction verbatim

Routine Bash Gate (once per session)

1. The current user request in one sentence
2. What this specific command verifies or produces

Read-only introspection does not use this gate up: until it fires, a command whose every ;, |, && or || segment is ls, pwd, cat, head, tail, wc, grep, rg, find, fd, tree, or git status/log/ diff/show/ls-files/rev-parse/branch with read-only options (in PowerShell: Get-ChildItem, Get-Content, Select-String, Get-Location, their aliases, rg, git) passes and is counted in routine_readonly_passes. The first other command is still gated. Any redirection, tee, substitution, backtick, variable, environment assignment, wrapper (env, sudo, xargs, sh -c), unknown command, find -exec/-delete, fd -x, rg --pre/-z, tree -o, git global option or write/execute option, or PowerShell $, @, (, { or --% makes the command ordinary. Destructive detection runs first, unchanged.

Session state expires after 8 idle hours when it is keyed by a session id or transcript path, and after 30 idle minutes when it falls back to the project directory.

Parallel Batches and Partial Application

The first-touch gate evaluates each tool call independently. When several edits to a file that has not been touched yet are sent in one parallel batch, the first call is denied and the denial marks the file as checked, so the sibling edits in that batch are applied. Nothing is rolled back: the file can end up holding the sibling edits without the denied one.

The denial message names the file and warns that batch siblings may already have been applied. Treat it literally:

• Send dependent edits to a not-yet-touched file sequentially, not in a parallel batch. A definition and its first use, or an import and its call site, must not ride in the same batch.
• After a first-touch denial, present the facts, retry the denied edit, and re-read the file before building on anything else from the batch.

A batch-wide lock is not possible: hooks see tool calls one at a time, so the gate cannot know which calls arrived together.

What Counts as Already Done

A first-touch denial is meant to force investigation. When the transcript shows the investigation already happened, or the answers would repeat the previous denial word for word, the gate lets the call through with a note instead of a denial. Each rule below falls back to the normal denial when anything is ambiguous.

Order of checks

For each Edit/Write/NotebookEdit target (and each MultiEdit entry) the gate decides in this order; the first rule that applies wins:

1. Exempt (GATEGUARD_EXEMPT_GLOBS, Claude settings files) — allowed. Operator exemptions are authoritative: they win over every later rule, including the sensitive and hard-link rules, so a glob that covers src/auth/** or a hard-linked file turns its check off. Exempt only paths that may be edited without the check.
2. Subagent call — allowed (the parent session was already gated), except a sensitive or hard-linked target: denied once per path unless the parent already gated it. A subagent's retry does not unlock the path for the parent.
3. Already checked this session — allowed.
4. Sensitive or hard-linked target? — if so, skip straight to the denial (step 9).
5. Prior-search credit — allowed with a note.
6. Comment or whitespace-only Edit — allowed with a note, not marked checked.
7. Sibling collapse — allowed with a note.
8. Denial cap (GATEGUARD_FACT_FORCE_MAX_DENIALS, opt-in) — passes through once the session's denials have reached the cap.
9. Deny — counted in fact_force_denials.

Credit, trivial and sibling allows never consume the denial cap.

Sensitive targets

Some files are too costly to change without the full check, so prior-search credit, the comment or whitespace-only pass, the change profile, sibling collapse, and the denial cap never apply to them: they are denied on first touch exactly as without these rules, and the denial counts as usual. The denial carries one extra line: "Sensitive target: prior-search credit, sibling collapse, and the denial cap do not apply." A target is sensitive, judged on the same lowercased project-relative path as its class and on its real (symlink-resolved) location, when either matches:

• its file name is .env, .netrc, or .pgpass, starts with .env., ends in .pem, .key, .p12, or .pfx, or starts with id_rsa, id_ed25519, id_ecdsa, id_dsa, credentials, or secrets.;
• any path segment is exactly auth, authn, authz, security, secrets, payment, payments, billing, or migrations (whole segments only: src/author.py, docs/authoring.md, and lib/paymentutils.py are ordinary);
• or it lies under .github/workflows/.

The real location is the file's own realpath when it exists, else the realpath of its nearest existing directory plus the rest of the path, judged relative to the realpath of the project root, so src/tools -> ../auth makes src/tools/login.py sensitive. A real location outside the project is judged on its absolute path. Any error while deciding (a dangling symlink, a file where a directory should be, a permission error) counts as sensitive. Destructive and routine shell gates are unaffected.

Hard-linked targets

A file with more than one hard link (nlink > 1, or a symlink to such a file) is also reachable under another name, which may be sensitive or in another class, so the path being edited says little about what changes. It gets the same treatment as a sensitive target — no prior-search credit, change profile, comment-only pass, sibling collapse, denial cap, or subagent bypass — and its denial carries "Hard-linked target: prior-search credit, sibling collapse, and the denial cap do not apply." instead of the sensitive line (a target that is both says "Sensitive target"). A stat error other than a missing file counts as hard-linked; a new file that does not exist yet is not.

Prior-search credit

An Edit, Write, NotebookEdit, or MultiEdit entry is allowed, with an additionalContext note naming the search, when a qualifying search in the current human turn already covered the file:

• Qualifying tools: Glob, Grep, LS, and Bash/PowerShell command segments led by rg, grep, egrep, fgrep, git grep, git ls-files, find, fd, ls, tree, Get-ChildItem, gci, Select-String, or sls. Read never counts — Claude Code already requires a Read before an Edit, so it proves nothing extra.
• Current human turn: the turn starts at the latest real user message or at a compaction (a compact-summary record or a compact_boundary marker), so searches from before a compaction never count. Tool results, meta, and sidechain records do not start a turn. Only the transcript tail is read (last 256 KiB / 2000 lines); when the turn started before that window, the whole window is the current turn, provided every promptId in it agrees. Two or more promptIds there mean a turn started through a record the scan does not recognise, so that window gives no credit. A transcript with no turn start at all gives no credit.
• Completed, unambiguous result: the search needs a tool_result in the turn that is not an error (is_error of true or "true", or content starting with <tool_use_error>). A tool-use id that appears more than once never counts.
• Not the same batch: searches sent in the gated call's own assistant message never count, since their results were not seen when the edit was decided. If the payload's tool_use_id is missing or not in the transcript, the newest assistant message in the turn is excluded instead. A search without a message id never counts.
• Stem match: the target's stem (basename minus its last extension, lowercased, at least 4 characters) must appear as a whole word — bounded by non-alphanumeric characters or the ends of the text — in the Glob pattern, the Grep pattern or glob, or the shell segment. payment.py is credited by a search for payment or payment_service, but not by one for payments. Exclusions are never a stem source. Generic stems (index, main, init, __init__, utils, util, types, readme, test, tests, config, mod, lib, setup, app, spec, helpers, common) never match. For a test target, one test affix is stripped first (.test, .spec, and for Python and Go test_ or _test), so rg tokenizer src tests credits tests/tokenizer.test.js; index.test.js still reduces to the generic index.
• Exclusions never credit: a Grep glob is split on top-level commas; entries starting with ! are exclusions. In shell segments, rg -g/ --glob/--iglob values starting with !, grep --exclude/ --exclude-dir, fd -E/--exclude, ls -I/--ignore/--hide, tree -I, git ls-files -x, git :!x/:^x/:(exclude)x pathspecs, find -name/-path/… under -not or ! or followed by -prune, and PowerShell -Exclude are exclusions. If an exclusion covers the target (its glob matches the file name or any directory on its path, or it names the stem), that search cannot credit the target at all: rg -g '!widget.py' TODO . never credits widget.py, while rg -g '!*.md' widget . still does. --exclude-from, --ignore-file, and git ls-files -X hide names the hook cannot see, so such a segment never credits. File-name globs that restrict a search (Grep glob: '*.py', rg -g '*.py', grep --include, find -name, tree -P, -Include/-Filter) must match the target's file name for its stem to count. File types filter the same way: rg -t/ --type and the Grep type include the type's globs, rg -T/--type-not exclude them, and fd -e/--extension includes *.<ext>, so rg -t py tokenizer src never credits tokenizer.js. An unknown type name, --type-add, or --type-clear makes the segment never credit.
• Lookups are not searches: a search confined to the target's own file name — every include glob, the Glob pattern, or every path pattern ends in that exact name (Glob **/tokenizer.js, find -name tokenizer.js, rg -g tokenizer.js, Grep glob: 'tokenizer.js') — could only find the target, so it never credits it. Glob **/tokenizer.* still does.
• Scope: Glob, Grep, and LS only credit a target strictly inside the directory they searched (their path, else the tool cwd, plus a Glob pattern's literal leading directories). A Glob pattern is a filter too: it must match the target's path for the stem to count, so Glob **/tokenizer.py never credits tokenizer.js. A Glob without glob characters is a one-file lookup: it names no directory and credits only files directly in its directory, never the looked-up file itself. A search whose path is the target is not a search.
• Shell segments: a segment without a path operand counts only when it is recursive (rg, git grep, git ls-files, find, fd, and tree by default; grep -r/-R/--recursive, ls -R, Get-ChildItem -Recurse) and not fed by a pipe; otherwise it reads stdin, not the tree. A segment whose path operands all resolve to the target only reads the target and does not count (ls src/a.py never credits src/a.py). Commands containing $( ), backticks, <( ), >( ), or heredocs, or longer than 8192 characters, never credit.
• Shell scope: a shell segment only credits a target equal to or inside one of its path operands (resolved against the tool cwd; a glob operand must match the target or a directory above it, and a default git pathspec's * also matches /), or inside the cwd when it has none: rg payment docs or grep -rn payment /usr/share/doc never credit src/payment.py. An input redirection before any operand (rg payment < file) or a < inside a word reads stdin and never counts. After cd <dir> in the same command, relative operands resolve against that directory; after any other directory change, or one in another call of the turn, only absolute operands count.
• Directory match (new files only): a Write that creates a file that does not exist yet may also match when the search named exactly the target's directory: a Glob path plus the pattern's literal prefix (a pattern that starts with a glob character and has no path names no directory), a Grep or LS path, or a shell path operand. For shell operands, the pattern argument of grep-style tools is skipped (unless -e/-f/--regexp/--file/-Pattern supplied the pattern), values of value-taking flags (-g, --include, -name, -Filter, …) are skipped, trailing /, /*, and /** are dropped, ., ~/$ paths, and globs name no directory, and the operand must be an existing directory at the time of the check. If any Bash/PowerShell call in the turn changes directory (cd, pushd, popd, chdir, Set-Location, sl, Push-Location, Pop-Location), shell directory matching is off for the whole turn; stem matching still applies. Edit, MultiEdit, and a Write that overwrites an existing file match by stem only.
• Paths: relative targets and search paths resolve against the tool's cwd, then CLAUDE_PROJECT_DIR, then the process directory. Comparison is case-insensitive for Windows paths only. Shell commands are read with bash quoting rules, so on Windows an operand credits when spelled C:/x/src; backslash spellings (C:\x\src, quoted or not) and MSYS spellings (/c/x/src) do not credit and the write is denied as usual.
• Note, not denial: the credited file is marked checked and fact_force_credited is incremented; the denial count and ordinal are not touched. MultiEdit credits per entry and denies the first uncredited entry as before.
• Falls back to deny: a missing, unreadable, or non-file transcript, garbage records, or any internal error mean no credit.
• Closest miss in the denial: when an ordinary (not sensitive or hard-linked) first touch is denied and a call in the turn mentioned the file without crediting it, the denial adds one line, "Closest search this turn did not count (<tool> <detail>): <why>.", naming the closest such call and why it failed: sent in the same batch, its filters exclude the file, its search path does not contain it, it searched piped input, it was a Read or another command rather than a search, or the file name is too generic to match. The detail is sanitized and cut to 60 characters; no other transcript text is shown.

Comment and whitespace-only edits

An Edit whose old and new text differ only in comments and whitespace changes no behaviour, so the first-touch questions carry no signal. Such an Edit (or a MultiEdit whose entries for that file are all such changes) of a code, test, or prose target that is not sensitive passes with the note "Comment or whitespace-only change to <file>". The file is not marked checked: the next change to it that alters code meets the normal first-touch gate. The pass is counted in trivial_allows and never touches the denial count.

It applies only to the extensions listed in Questions fit the change, and only when every entry reads cleanly:

• comments are // and /* */ (C family), # (Python), # at the start of a word (shell), # and <# #> (PowerShell), or REM lines (batch); C preprocessor lines and batch :: labels are code; directive comments are code too (shebangs, encoding cookies, # type:, # noqa, # nosec, // @ts-..., eslint-..., //go:build, // +build, //go:embed, Rust doc comments, #Requires, shellcheck, NOLINT, NOSONAR, fallthrough markers and similar); whitespace inside strings, line breaks between code, and the presence of whitespace between tokens are code (a+b → a + b is not trivial);
• Python indentation of code lines is code;
• never trivial: a Write; any multi-line or raw string form (backticks, triple quotes, r", R", @", $", f-strings, Kotlin $), a string running to the end of a line, a line comment or code line ending in \, ??/, a nested or unterminated block comment; in JS/TS any / outside a comment (regex versus division), JSX-like tags, and -->; in shell scripts heredocs, backticks, $( inside double quotes, $'...', line continuations and here-strings (see the design notes for the full list);
• config, instruction, sensitive and hard-linked targets, and NotebookEdit calls never pass this way.

The edit is also checked against the current file (a regular file of at most 1 MiB, read by the hook and never stored): old_string must be found as the Edit tool would apply it, the lines around the change must compare equal as above, and the text before them must end in plain code, not inside a template literal, docstring, raw string, heredoc or here-string and not after a line continuation. A missing, unreadable or larger file, or a Go file that imports "C", never passes this way.

Same-turn sibling creation collapse

When several new files are created in one directory, the answers for each would be identical, so only the first is denied:

• Applies to a Write of a file that does not exist yet whose class is code, test, or prose. Never collapsed: config and instruction files, and any path with a segment starting with . (dotfiles and every dot-directory: .claude, .github, .git, .husky, .devcontainer, .githooks, .idea, .vscode, …) or an 8.3 short name (CLAUDE~1), checked on the same project-relative path as the class.
• The directory is also resolved to its real location (symlinks followed; missing directories are resolved from the nearest existing parent). If that differs from the path as written, the real path must be inside the project, keep the same class, and pass the same screen, so a symlink such as src/tools -> .claude/hooks never collapses. Gates are keyed by the real directory. Any filesystem error means no collapse.
• After such a Write is denied, later first-touch Writes of new files of the same class in the same directory are allowed with the note "Sibling of <first> (gated earlier at denial #<n> this session)". A code denial never lets a test, README, or config file through.
• The window is the same human turn. The turn id is the turn-start record's own promptId, else its uuid, else a hash of that record. When the turn started before the transcript tail, the id is the promptId that every user record in the window agrees on (Claude Code stamps it on the prompt and on every tool result of the turn); if they disagree there is no turn id. Only when no transcript path is available at all does a gate recorded without a turn id match for 120 seconds; a transcript that is missing, unreadable, or yields no turn id means no collapse. A turn-scoped gate never matches a call without a turn id, and vice versa; a gate stamped in the future is ignored.
• Prior-search credit is checked first. Edits and MultiEdits are never collapsed, and an existing file is never treated as a sibling.

Canonical path keys

Checked state is keyed on the canonical path: a relative file_path resolves against the tool's cwd (where the tool runs), then CLAUDE_PROJECT_DIR, then the process directory, with / separators, lowercased on Windows only. a.py, ./a.py, and the absolute path share one first-touch. State files written by earlier versions (raw keys) are still honoured. GATEGUARD_EXEMPT_GLOBS keeps its project-relative matching (below).

In-session counters

The per-session state file (under GATEGUARD_STATE_DIR) records these fields. They record class names only, never paths (except dir_gates, which stores the sanitized first file per directory):

Field	Meaning
fact_force_credited	Number of first touches allowed by prior-search credit
denials_by_class	Denials per target class (code, prose, test, …)
credited_by_class	Credits per target class
sibling_allows	Number of Writes allowed by sibling collapse
dir_gates	Per class and directory, the denial that opened a sibling window (turn, time, first file, ordinal); capped at 50 entries
cap_allows	Number of first touches passed through by the denial cap (GATEGUARD_FACT_FORCE_MAX_DENIALS); these never count as denials
trivial_allows	Number of comment or whitespace-only edits passed without the first-touch check; these never mark the file checked
routine_readonly_passes	Number of read-only shell commands passed before the routine shell gate fired; these never mark it checked

Missing or malformed fields load as empty or zero, so older state files keep working.

Compatibility and limits

• Two new, opt-in environment variables: GATEGUARD_FACT_FORCE_MAX_DENIALS (unset means no cap) and GATEGUARD_METRICS (unset means no metrics). The existing controls are unchanged.
• Nothing previously allowed is now denied, except a subagent's first touch of a sensitive or hard-linked target, and the first NotebookEdit of each notebook (NotebookEdit was not gated before). The other rules only remove denials, and never return permissionDecision: "allow", so other hooks and permission rules still apply.
• Trust limit: prior-search credit reads the local transcript file, which the agent could in principle write to. The credit verifies observed behaviour (a search ran and returned), not intent or how carefully the result was read.

Quick Start

Option A: Use the ECC hook (zero install)

The hook at scripts/hooks/gateguard-fact-force.js is included in this plugin. Enable it via hooks.json.

If GateGuard blocks setup or repair work, start the session with ECC_GATEGUARD=off. For hook-level control, keep using ECC_DISABLED_HOOKS with the GateGuard hook ID.

In long sessions, only the first GATEGUARD_FACT_FORCE_FULL_DENIALS fact-force denials (default 3) emit the full fact block; later denials are condensed to a single line carrying the denial ordinal, so near-identical blocks cannot accumulate in the context window and amplify model repetition loops (#2142). Retrying the same file or command after presenting facts never re-triggers the gate. That is a message budget; to stop denying new files after a number of denials, set the opt-in denial budget GATEGUARD_FACT_FORCE_MAX_DENIALS (below).

Graduated controls

ECC_GATEGUARD=off (or GATEGUARD_DISABLED=1) turns the gate off entirely. The variables in this table do not — each narrows one behaviour while the load-bearing destructive-Bash checks keep running:

Variable	Default	Effect
GATEGUARD_BASH_ROUTINE_DISABLED	unset (gate on)	Disables the routine-Bash gate only. The destructive-Bash gate (rm -rf, git reset --hard, drop table, dd if=, …) is unaffected.
GATEGUARD_EXEMPT_GLOBS	unset (no exemptions)	Comma-separated globs; a matching Edit/Write/MultiEdit/NotebookEdit target skips first-touch fact-forcing, even when it is sensitive or hard-linked. Intended for low-import-value trees (tests, generated artifacts, scratch dirs) where "who imports this / what schema" carries no signal.
GATEGUARD_FACT_FORCE_FULL_DENIALS	3	How many denials emit the full fact block before later ones condense to a single line. 0 condenses from the very first denial.
GATEGUARD_FACT_FORCE_MAX_DENIALS	unset (no cap)	A denial budget: caps how many first-touch Edit/Write/MultiEdit/NotebookEdit denials a session draws. Once that many denials have been issued, further new paths pass through instead of being denied (counted in cap_allows, not as denials); 0 passes from the first. Prior-search credit and sibling collapse run first and never use it up, and sensitive and hard-linked targets are always denied. Destructive and routine Bash stay gated. The cap is best effort when hooks run concurrently: a lost count update can add a denial, but never lets a new path through early. Opt-in: unset, or any value that is not a whole non-negative integer (surrounding spaces allowed), keeps the deny-every-new-path behaviour; a malformed value is reported once on stderr (ignoring malformed GATEGUARD_FACT_FORCE_MAX_DENIALS=…; the denial cap is not active.). Unlike GATEGUARD_FACT_FORCE_FULL_DENIALS, a message budget that only changes how much text a denial carries, this changes whether the operation is blocked. Condensed denials name this variable.
GATEGUARD_BASH_EXTRA_DESTRUCTIVE	unset	Extra destructive-command patterns, as regex source, added to the built-in set. A malformed regex is treated as unset (built-ins still apply) and logged once to stderr.
GATEGUARD_STATE_DIR	~/.gateguard	Where per-session gate state is kept. If state cannot be persisted the gate allows the operation rather than looping, and names this variable in the warning.
GATEGUARD_METRICS	unset (off)	Records one line per Edit/Write/MultiEdit/NotebookEdit/Bash/PowerShell decision in <GATEGUARD_STATE_DIR>/metrics.jsonl (see Decision metrics). Never changes a decision.
GATEGUARD_EXTERNAL_CONTRACT_QUESTION	unset (off)	Adds a code question after the data-schema question: name what outside the repository decides the format, units, timezone or protocol semantics. Experimental: in hidden-intent trials it did not change outcomes (docs/gateguard/question-effectiveness.md). Never changes a decision.

GATEGUARD_BASH_ROUTINE_DISABLED, GATEGUARD_METRICS and GATEGUARD_EXTERNAL_CONTRACT_QUESTION accept 1, true, on, enabled, enable, or yes (case- and whitespace-insensitive); any other value leaves the routine gate on, metrics off, and the question unasked.

Decision metrics

With GATEGUARD_METRICS=1, each gate decision appends one JSON line to metrics.jsonl in the state directory (a MultiEdit call writes one line per file it decided):

{"v":1,"ts":"2026-09-01T10:02:00.000Z","session":"3f9c0a1b2d4e","tool":"Edit","class":"code","decision":"deny","reason":"near-miss:out-of-scope","questions":["local-callers","quote-instruction"],"sensitive":false,"profile":{"known":true,"language":"js","touchesPublicSurface":false,"touchesData":false,"trivial":false}}

Field	Meaning
v	Schema version (1)
session	First 12 hex characters of the sha256 of the session key
tool	Edit, Write, MultiEdit, NotebookEdit, Bash or PowerShell
class	Target class, or null for shell commands
decision	deny, credit, sibling, cap, trivial, pass-checked, pass-exempt, pass-subagent, routine-deny, routine-readonly, destructive-deny or pass
reason	Short code: first-touch, sensitive, hard-linked, near-miss:<code>, subagent-sensitive, subagent-hard-linked, prior-search, comment-whitespace, same-turn-dir, max-denials, checked, exempt-glob, claude-settings, no-path, subagent, readonly-git, readonly, first-command, routine-checked, routine-disabled, destructive, destructive-retry, state-error
questions	Question ids of a first-touch denial; null otherwise
sensitive	Whether the target is a sensitive target
profile	Change-profile flags when the profile was computed; null otherwise

Privacy: lines never contain paths, commands, file content, transcript text or the session id itself; every text field must be a short lowercase code or is written as null. Metrics errors are ignored. Past 1 MiB the file is renamed to metrics.jsonl.1, replacing the previous one.

Summarise the metrics with:

node scripts/gateguard-report.js            # GATEGUARD_STATE_DIR or ~/.gateguard
node scripts/gateguard-report.js --dir /path/to/state --json

It reads metrics.jsonl.1 then metrics.jsonl, skips malformed lines, and prints, per session and in total: decisions by type, denials by class and reason, the share of first-touch denials that followed a near-miss search, the rates of denial, credit, sibling collapse, cap and trivial edits among first touches, routine read-only passes, and the most-asked question ids.

Turning the gate off completely

Variable	Effect
ECC_GATEGUARD=off	Disables GateGuard for the session. Accepts 0, false, off, disabled, or disable.
GATEGUARD_DISABLED=1	Same effect. Recognises 1 only — the spellings above do not apply here.

For hook-level control, keep using ECC_DISABLED_HOOKS with the GateGuard hook ID.

Glob semantics for GATEGUARD_EXEMPT_GLOBS

Patterns match the entire project-relative target path. The project root is CLAUDE_PROJECT_DIR, falling back to the hook payload's cwd, then the hook process working directory. Relative globs never exempt targets outside that root. Explicit absolute globs match the entire absolute target path and may deliberately exempt paths outside the project.

Both patterns and paths use / separators and lowercase matching. * matches within a segment, ** across segments, and ? one non-separator character. **/ includes zero directories, so **/tests/** also matches tests/foo.js. Malformed patterns are dropped without granting an exemption. An exemption applies before every other rule, including the sensitive and hard-link rules (see Order of checks).

Since 2.2.1, services/** only covers the project's root services tree, and *.md only covers its root Markdown files. Use **/*.md for all Markdown files within the project. Existing unanchored exemptions may need adjustment:

{
  "env": {
    "GATEGUARD_BASH_ROUTINE_DISABLED": "1",
    "GATEGUARD_EXEMPT_GLOBS": "**/tests/**,tests/**,**/*.test.*,**/docs/**,**/dist/**"
  }
}

Option B: Full package with config

pip install gateguard-ai
gateguard init

This adds .gateguard.yml for per-project configuration (custom messages, ignore paths, gate toggles).

Anti-Patterns

• Don't use self-evaluation instead. "Are you sure?" always gets "yes." This is experimentally verified.
• Don't skip the data schema check. Both A/B test agents assumed ISO-8601 dates when real data used %Y/%m/%d %H:%M. Checking data structure (with redacted values) prevents this entire class of bugs.
• Don't gate every single Bash command. Routine bash gates once per session. Destructive bash gates every time. This balance avoids slowdown while catching real risks.

Best Practices

• Let the gate fire naturally. Don't try to pre-answer the gate questions — the investigation itself is what improves quality. A real search for the target before editing is investigation, and is credited (see What Counts as Already Done).
• Customize gate messages for your domain. If your project has specific conventions, add them to the gate prompts.
• Use .gateguard.yml to ignore paths like .venv/, node_modules/, .git/.

Related Skills

• safety-guard — Runtime safety checks (complementary, not overlapping)
• code-reviewer — Post-edit review (GateGuard is pre-edit investigation)