ast-grep

name	ast-grep
description	Use when searching or replacing code patterns - use ast-grep instead of text search for semantic accuracy

AST-Grep Code Search

Use ast_grep_search and ast_grep_replace for semantic code search/replace. ast-grep understands code structure, not just text.

When to Use

• Function calls, imports, class methods (structured code)
• Safe replacements across files
• Use LSP first for: definitions/references/types — then scope ast-grep to files discovered by LSP
• Use grep for: partial string patterns, comments, URLs, or after one simplified ast-grep retry still returns zero matches

Golden Rules

1. Be specific — fetchMetrics($ARGS) not fetchMetrics
2. Scope it — always specify paths to relevant files
3. Retry once on zero matches — simplify the pattern, same paths, then fall back to grep
4. Dry-run first — apply: false before apply: true
5. Valid code only — function $NAME($$$) { $$$ } not function $NAME(
6. Avoid selector unless expert — narrows to AST node kind; does not extract metavariables
7. Metavariables don't work inside strings — from "$PATH" matches literal "$PATH", not a wildcard

Metavariables

Syntax	Matches	Named?
$X	single node	yes — captures the node
$$$	zero or more nodes	no — unnamed wildcard
$$$ARGS	zero or more nodes	yes — captures the list

Use $$$ when you don't need the captured value; $$$NAME when you do.

Quick Reference

Patterns

Pattern	Matches
fetchMetrics($ARGS)	call with any single arg
fetchMetrics($$$ARGS)	call with any number of args
function $NAME($$$) { $$$ }	function declaration
import { $NAMES } from $PATH	named import (no quotes on path)
const $X = $Y	variable declaration

Structural-intent parameters (preferred for cross-context queries)

Use these instead of writing raw YAML:

Parameter	What it does
insideKind	Only match inside an ancestor of this node kind
hasKind	Only match nodes that contain a descendant of this kind
follows	Only match nodes preceded by a sibling matching this pattern
precedes	Only match nodes followed by a sibling matching this pattern

# console.log only inside functions
ast_grep_search pattern="console.log($MSG)" lang="typescript" insideKind="function_declaration"

# replace var with let, scoped to functions only
ast_grep_replace pattern="var $X" rewrite="let $X" lang="javascript" insideKind="function_declaration"

These synthesize a YAML rule automatically. Use rule: for the full DSL when you need all/any/not, nthChild, regex, or other advanced constraints.

Raw YAML rule (rule: parameter)

Pass a complete ast-grep YAML rule to unlock the full DSL:

ast_grep_search rule="id: my-rule
language: TypeScript
rule:
  pattern: console.log($MSG)
  inside:
    kind: function_declaration
    stopBy: end" lang="typescript"

Debugging unknown node kinds — ast_dump

When a pattern returns zero matches and you don't know the correct node kind or field name, use ast_dump to inspect the AST:

ast_dump source="function foo() { return 1; }" lang="typescript"

Returns the full indented AST with node kinds and positions. Then use the correct kind in your pattern or insideKind.

Composite (has/inside) in raw YAML

# console.log inside a class method
pattern: console.log($$$)
inside:
  kind: method_definition
  stopBy: end

Use kind: directly when you want to match a node type without a pattern:

# any arrow function
kind: arrow_function

Common Gotchas

❌ $VAR inside quotes — matches literal "$VAR", not a metavar
   from "$PATH"  →  use grep for wildcard path matching
   from "./utils"  →  ✅ exact string literal works fine

❌ Trailing comma in objects
   { type: $T, }  →  use { type: $T }

❌ Shorthand property mismatch
   { runnerId: $RID }  →  won't match { runnerId }
   use { runnerId } or { runnerId, $$$REST }

❌ Unnamed $$$ when you need the value
   foo($$$)  →  captures nothing; use foo($$$ARGS) to inspect matches

❌ Multiple top-level statements — triggers "Multiple AST nodes are detected"
   Two shapes, two fixes:

   1. Sequence inside a block — wrap in braces:
      foo(); bar();  →  { foo(); bar(); }

   2. Cross-context (module-level + block-level together, e.g. an import AND a call) —
      wrapping in {} makes the pattern invalid (imports can't live inside a block).
      Use two searches: find files containing the import, then scope the call search
      to those paths. Or use a YAML `inside:`/`has:` rule (see Composite section above).

No matches?

1. Try strictness: relaxed — ignores unnamed punctuation (trailing commas, semicolons) that smart mode requires
2. Use ast_dump on a sample snippet to verify the correct node kind
3. Simplify the pattern and retry once
4. Fall back to grep or lsp_navigation

Metavar captures appear automatically below each match line:

src/foo.ts:1:1: const x = foo(a, b)
  $VAR=x  $$$ARGS=a,b

Named captures ($X, $$$NAME) are shown; unnamed wildcards ($$$) are not.

Pagination — use skip: N when results are truncated (next-page hint appears in output).

Debug: https://ast-grep.github.io/playground.html