FastAST — Application Map & Architectural Tour

High-performance AST repository indexer & SQLite graph database for AI coding agents

✓ Verified Proof of Concept Ready

1. Plain-Language Overview

FastAST is an ultra-fast, AST-based repository indexer designed for AI coding agents and developers. Instead of reading whole repositories blindly or relying on fuzzy regex grep, FastAST parses code into syntax trees across 9 languages using native Tree-Sitter and indexes all files, symbols, imports, and function calls into a persistent SQLite database.

AI coding agents connect via the standard Model Context Protocol (MCP) to query symbol definitions, find references, and explore call graphs instantly without exhausting token context budgets.

2. Core Execution Journey

3. The 3-Stop Architecture Route

Stop 1: Native Tree-Sitter AST Engine

src/lib.rs & src/<language>/mod.rs

Parses source files into Tree-Sitter AST nodes across 9 languages (Python, Java, JavaScript, TypeScript, Rust, HTML, CSS, JSON, TOML). Extracts classes, methods, functions, module imports, and invocation calls into structured FileIndexResult structs.

Stop 2: SQLite Relational Index Store

python/fastast/indexer.py

Walks the repository honoring ignore rules (.git, node_modules, target, .venv). Populates indexed tables (files, symbols, imports, calls) and provides high-speed query methods (find_symbol, get_calls_from_symbol).

Stop 3: MCP Server & CLI Runner

python/fastast/server.py & python/fastast/cli.py

Connects coding agents and developers to the index. Exposes index_repository, query_symbols, and get_call_graph over stdio JSON-RPC for Claude Code and Cursor, plus terminal CLI commands (index, symbols, calls).

4. To Change This, Start Here

To add a new language: Add Tree-Sitter grammar to Cargo.toml and implement index_code in src/<lang>/mod.rs.
To customize indexed fields or tables: Modify the SQL schema in RepositoryIndexer.init_db() in python/fastast/indexer.py.
To add new agent tools: Define new @mcp.tool() endpoints in python/fastast/server.py.
To customize ignore patterns: Update DEFAULT_IGNORES in python/fastast/indexer.py.

5. How to Run & Verify

# 1. Index a repository:
fastast index . --db fastast.db

# 2. Query symbols:
fastast symbols fastast.db --query "index"

# 3. Trace call graph:
fastast calls fastast.db --symbol "main"

# 4. Start the MCP server:
fastast-mcp --db fastast.db