Rule Engine

Rule Engine#

The rule engine lets you customize review behavior per file and per PR using a declarative expression language. Rules are defined in the [[rules]] array in your config file.

Rule Structure#

toml

[[rules]]
name = "skip-generated"
condition = 'file.path matches ".*\\.gen\\..*"'
priority = 10

[[rules.actions]]
type = "skip_file"

Each rule has:

name – a human-readable label (required)
condition – an expression that evaluates to a boolean (required)
priority – rules with higher priority are evaluated first (default: 0)
actions – a list of actions executed when the condition is true

Expression Language#

Grammar#

Expressions follow this precedence (lowest to highest):

|| (logical OR)
&& (logical AND)
! (logical NOT, prefix)
Comparison: ==, !=, >, <, >=, <=
Membership: in [...]
String operations: matches, contains, starts_with, ends_with
Arithmetic: +
Primaries: identifiers, numbers, strings, booleans, parenthesized expressions

Keywords and, or, not are accepted as aliases for &&, ||, !.

Operators#

Operator	Syntax	Description
&& / and	a && b	Short-circuit logical AND
\|\| / or	a \|\| b	Short-circuit logical OR
! / not	!a	Logical negation
==	a == b	Equality (cross-type for numbers and strings)
!=	a != b	Inequality
>	a > b	Greater than
<	a < b	Less than
>=	a >= b	Greater than or equal
<=	a <= b	Less than or equal
+	a + b	Numeric addition
in	a in [b, c]	Membership test against a list
matches	a matches "regex"	Regex match (full Rust regex syntax)
contains	a contains "substr"	Substring test
starts_with	a starts_with "prefix"	String prefix test
ends_with	a ends_with "suffix"	String suffix test

Literals#

Strings: double-quoted "hello" or single-quoted 'hello' with backslash escapes
Numbers: integer or decimal (42, 3.14)
Booleans: true, false

Available Variables#

Variables are accessed with dot notation. Not all variables are available in every context – file-level variables are only present when the rule is evaluated per file.

file.* (per-file context)#

Variable	Type	Description
file.path	string	Full file path relative to the repo root
file.extension / file.ext	string	File extension without the dot (e.g. "rs", "ts")

pr.* (per-PR context)#

Variable	Type	Description
pr.author	string	GitHub login of the PR author
pr.title	string	PR title text
pr.additions	number	Total lines added in the PR
pr.deletions	number	Total lines deleted in the PR

diff.* (per-file context)#

Variable	Type	Description
diff.additions	number	Lines added in this specific file
diff.deletions	number	Lines deleted in this specific file

Action Types#

Each action is a table with a type field and type-specific parameters.

skip_file#

Exclude the current file from review. No additional fields.

toml

[[rules.actions]]
type = "skip_file"

add_focus#

Add a focus area to the review prompt.

toml

[[rules.actions]]
type = "add_focus"
area = "Check for SQL injection vulnerabilities"

set_severity#

Override the review severity level.

toml

[[rules.actions]]
type = "set_severity"
level = "critical"

add_comment#

Inject a comment into the review context.

toml

[[rules.actions]]
type = "add_comment"
text = "This file is part of the auth subsystem. Review with extra care."

add_instruction#

Add a custom instruction to the LLM system prompt.

toml

[[rules.actions]]
type = "add_instruction"
text = "Verify that all database queries use parameterized statements."

set_review_depth#

Control how thorough the review should be.

toml

[[rules.actions]]
type = "set_review_depth"
depth = "thorough"

add_label#

Add a label to the review output (for downstream processing).

toml

[[rules.actions]]
type = "add_label"
label = "security-review"

Examples#

Skip Generated and Vendored Files#

toml

[[rules]]
name = "skip-generated"
condition = 'file.path matches ".*\\.gen\\..*" || file.path starts_with "vendor/"'
priority = 100

[[rules.actions]]
type = "skip_file"

Strict Review for Security-Sensitive Files#

toml

[[rules]]
name = "security-critical"
condition = 'file.path contains "auth" || file.path contains "crypto" || file.extension in ["sql", "sh"]'
priority = 50

[[rules.actions]]
type = "add_focus"
area = "Check for authentication bypass, injection, and credential leaks"

[[rules.actions]]
type = "set_severity"
level = "critical"

Flag Large PRs#

toml

[[rules]]
name = "large-pr-warning"
condition = "pr.additions + pr.deletions > 500"
priority = 10

[[rules.actions]]
type = "add_comment"
text = "This is a large PR. Consider splitting it into smaller, focused changes."

[[rules.actions]]
type = "set_review_depth"
depth = "thorough"

Skip Specific Authors#

toml

[[rules]]
name = "skip-bot"
condition = 'pr.author == "dependabot[bot]" || pr.author == "renovate[bot]"'
priority = 200

[[rules.actions]]
type = "skip_file"

Focus on Config File Changes#

toml

[[rules]]
name = "config-review"
condition = 'file.extension in ["toml", "yaml", "yml", "json", "env"]'
priority = 30

[[rules.actions]]
type = "add_focus"
area = "Verify no secrets are committed and default values are sensible"

[[rules.actions]]
type = "add_label"
label = "config-change"