# cx
Semantic code navigation for AI agents — file overviews, symbol search, definitions, and references — without running a language server.
> Disclaimer: Built with AI.
## Install
```bash
Or with Cargo:
```
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:
```bash
# 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.
## How cx compares
| **ctags** | Symbol indexing | Tree-sitter instead of regex, persistent db, built-in query CLI |
| **LSP** | Go-to-definition, find references, symbol search | No daemon, no compilation, no project setup — just parse and query |
| **ripgrep** | Finding code by name | Semantic — `cx definition --name X` vs grep-then-read-5-files |
| **Reading files** | Understanding code | `cx overview` ~200 tokens vs full file read ~thousands |
## 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.
Language grammars are downloaded on demand as shared libraries via [tree-sitter-language-pack](https://github.com/kreuzberg-dev/tree-sitter-language-pack). Install the ones you need:
```bash
cx lang add rust typescript python
cx lang list # see what's installed
cx lang remove lua # remove one
```
If you run cx without installing grammars first, it will tell you which ones are needed:
```
cx: no language grammars installed
Detected languages in this project:
rust (42 files)
typescript (18 files)
Install with: cx lang add rust typescript
```
**Supported languages:** Run `cx lang list` to see all supported languages and their install status.
**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](https://toonformat.dev) -- 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 loaded dynamically via `tree-sitter-language-pack`. To add support for a new language:
1. In `src/language/mod.rs`, add:
- A query constant with tree-sitter patterns for the language's symbols
- A `LanguageConfig` entry in the `LANGUAGES` array
2. Add tests
The grammar itself is downloaded at runtime — no build dependency needed. Here's a minimal example — adding Swift support:
```rust
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
"#;
LanguageConfig {
name: "swift",
extensions: &["swift"],
grammar_override: &[],
download_names: &[], // empty = download name matches config name
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 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`.
**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.
**Grammar names:** The `name` field must match the name used by `tree-sitter-language-pack` (check their [language list](https://github.com/kreuzberg-dev/tree-sitter-language-pack)). If the download name differs from the config name, use `download_names` (e.g., `typescript` also downloads `tsx`).