cx

Semantic code explorer for AI agents. The three LSP features they actually use — symbols, definitions, and references — without running a language server.

Alpha software. This is a work in progress — expect breaking changes. Built with AI assistance (Claude).

Install

cargo install cx-cli

Agent integration

cx skill prints a prompt that teaches any coding agent to prefer cx over raw file reads. Pipe it into whichever instructions file your agent reads:

# Claude Code (CLAUDE.md)
cx skill > ~/.claude/CX.md
# then add @CX.md to ~/.claude/CLAUDE.md

# Codex, Copilot, Zed, and other AGENTS.md-compatible tools
cx skill >> AGENTS.md

That's it. The prompt includes the command reference and the escalation hierarchy (overview → symbols → definition / references → read).

Why

Agents burn most of their context reading files. We analyzed 105 of our own Claude Code sessions (73 pre-cx, 32 post-cx) and found:

• 66% of reads are chains -- reading A to find B to find C, exploring before acting
• 37% are re-reads -- same file read multiple times per session
• Avg Read costs ~1,200 tokens (median 594), and sessions average 21 reads

cx gives agents a cost ladder. Start cheap, escalate only when needed:

cx overview src/fees.rs       ~200 tokens   "what's in this file?"
cx definition --name calc     ~200 tokens   "show me this function"
cx symbols --kind fn          ~70 tokens    "what functions exist in the codebase?"
cx references --name calc     ~1 query      "where is this used?"

In sessions with cx enabled, we measured 58% fewer Read calls and 40-55% fewer tokens spent on code navigation. The biggest wins are on chain reads and targeted lookups where cx overview or cx definition replaces a full file read.

Why not an LSP? Language servers are built for editors — persistent processes, 1-2GB RAM, per-language setup, and used by humans. Agents only need the ability to query the structure of their codebase. cx optimizes for that access pattern.

Usage

Overview -- file table of contents

$ cx overview src/main.rs

[9]{name,kind,signature}:
  Cli,struct,struct Cli
  Commands,enum,enum Commands
  main,fn,fn main()
  resolve_root,fn,"fn resolve_root(project: Option<PathBuf>) -> PathBuf"
  ...

Symbols -- search across the project

$ cx symbols --kind fn

[15]{file,name,kind,signature}:
  src/output.rs,print_toon,fn,"pub fn print_toon<T: Serialize>(value: &T)"
  src/query.rs,symbols,fn,"pub fn symbols(...) -> i32"
  src/query.rs,definition,fn,"pub fn definition(...) -> i32"
  ...

Filters: --kind, --name (glob), --file

Public/exported symbols are identifiable from their signatures (e.g. pub fn in Rust, export function in TypeScript).

Definition -- get a function body without reading the file

$ cx definition --name resolve_root

file: src/main.rs
line: 76
---
fn resolve_root(project: Option<PathBuf>) -> PathBuf {
    match project {
        Some(p) => p,
        None => {
            let cwd = env::current_dir().unwrap_or_else(|_| PathBuf::from("."));
            util::git::find_project_root(&cwd)
        }
    }
}

Use --from src/foo.rs to disambiguate when multiple files define the same name. --kind fn filters by symbol kind. --max-lines (default 200) truncates large bodies.

References -- find all usages of a symbol

$ cx references --name Symbol

[17]{file,line,kind,context}:
  src/index.rs,23,type_arguments,"pub exports: HashMap<PathBuf, Vec<Symbol>>,"
  src/index.rs,33,struct_item,"pub struct Symbol {"
  src/language/mod.rs,1,use_list,"use crate::index::{Language, Symbol, SymbolKind};"
  src/query.rs,43,field_declaration,"symbol: Symbol,"
  ...

The kind column shows the tree-sitter parent node type, indicating how the symbol is used (e.g. struct_item = definition, use_list = import, type_arguments = type reference).

Use --file src/index.rs to scope the search to a single file. Includes both definition and usage sites. Duplicate references on the same line are collapsed.

References are computed on-the-fly via AST walking (not indexed), so results are always fresh.

How it works

On first invocation, cx builds an index (.cx-index.db) by parsing all source files with tree-sitter. The index stores symbols, signatures, and byte ranges for every file. Subsequent invocations incrementally update only changed files.

Supported languages: Rust, TypeScript/JavaScript, Python, Go, C, C++, Java, Ruby, C#, Lua, Zig, Bash, Solidity, Elixir

Index location: .cx-index.db in the project root (add to .gitignore)

Project root detection: walks up from cwd looking for .git. Override with --root /path/to/project.

File filtering: cx respects your .gitignore. To exclude additional directories from indexing, drop an empty .cx-ignore file inside them.

Output format

Overview, symbols, and references use TOON -- a token-efficient structured format. Definition uses a plain-text format (metadata header + raw code body) for readability. Use --json for JSON on any command.

Adding a language

cx uses tree-sitter grammars. To add a new language:

1. Add the tree-sitter grammar crate to Cargo.toml
2. In src/language/mod.rs, add:
   • A grammar function (e.g., fn swift_grammar(_ext: &str) -> tree_sitter::Language)
   • A query constant with tree-sitter patterns for the language's symbols
   • A query function returning the constant
   • A LanguageConfig entry in the LANGUAGES array (including ref_node_types for find-references support)
3. Add the language variant to Language enum in src/index.rs
4. Add tests

Here's a minimal example — adding Swift support:

// Grammar function
fn swift_grammar(_ext: &str) -> tree_sitter::Language {
    tree_sitter_swift::LANGUAGE.into()
}

// Query — capture the patterns you care about
const SWIFT_QUERY: &str = r#"
(function_declaration
  name: (simple_identifier) @name) @definition.function

(class_declaration
  name: (type_identifier) @name) @definition.class

(protocol_declaration
  name: (type_identifier) @name) @definition.interface
"#;

fn swift_query() -> &'static str { SWIFT_QUERY }

// Registry entry
LanguageConfig {
    language: Language::Swift,
    extensions: &["swift"],
    grammar: swift_grammar,
    query: swift_query,
    sig_body_child: None,
    sig_delimiter: Some(b'{'),
    kind_overrides: &[],
    ref_node_types: &["simple_identifier", "type_identifier"],
},

Writing queries: Use tree-sitter parse or inspect node-types.json in the grammar crate to discover the AST structure. Capture @name for the symbol name and @definition.<kind> for the enclosing node. Supported kinds: function, method, class, interface, type, enum, module, constant, event, macro.

Kind overrides: When a language maps generic capture names to specific concepts (e.g., Rust's definition.class → SymbolKind::Struct), add entries to kind_overrides. These are checked before the default mapping.