opencode-codebase-index

opencode-codebase-index

Stop grepping for concepts. Start searching for meaning.

opencode-codebase-index brings semantic understanding to your OpenCode workflow. Instead of guessing function names or grepping for keywords, ask your codebase questions in plain English.

🚀 Why Use This?

• 🧠 Semantic Search: Finds "user authentication" logic even if the function is named check_creds.
• ⚡ Blazing Fast Indexing: Powered by a Rust native module using tree-sitter and usearch. Incremental updates take milliseconds.
• 🌿 Branch-Aware: Seamlessly handles git branch switches — reuses embeddings, filters stale results.
• 🔒 Privacy Focused: Your vector index is stored locally in your project.
• 🔌 Model Agnostic: Works out-of-the-box with GitHub Copilot, OpenAI, Gemini, or local Ollama models.

⚡ Quick Start

• Install the plugin

  npm install opencode-codebase-index
  

• Add to opencode.json

  {
    "plugin": ["opencode-codebase-index"]
  }
  

• Index your codebase Run /index or ask the agent to index your codebase. This only needs to be done once — subsequent updates are incremental.

• Start Searching Ask:

  "Find the function that handles credit card validation errors"

🔍 See It In Action

Scenario: You're new to a codebase and need to fix a bug in the payment flow.

Without Plugin (grep):

• grep "payment" . → 500 results (too many)
• grep "card" . → 200 results (mostly UI)
• grep "stripe" . → 50 results (maybe?)

With opencode-codebase-index: You ask: "Where is the payment validation logic?"

Plugin returns:

src/services/billing.ts:45  (Class PaymentValidator)
src/utils/stripe.ts:12      (Function validateCardToken)
src/api/checkout.ts:89      (Route handler for /pay)

🎯 When to Use What

Scenario	Tool	Why
Don't know the function name	codebase_search	Semantic search finds by meaning
Exploring unfamiliar codebase	codebase_search	Discovers related code across files
Know exact identifier	grep	Faster, finds all occurrences
Need ALL matches	grep	Semantic returns top N only
Mixed discovery + precision	/find (hybrid)	Best of both worlds

Rule of thumb: Semantic search for discovery → grep for precision.

📊 Token Usage

In our testing across open-source codebases (axios, express), we observed up to 90% reduction in token usage for conceptual queries like "find the error handling middleware".

Why It Saves Tokens

• Without plugin: Agent explores files, reads code, backtracks, explores more
• With plugin: Semantic search returns relevant code immediately → less exploration

Key Takeaways

• Significant savings possible: Up to 90% reduction in the best cases
• Results vary: Savings depend on query type, codebase structure, and agent behavior
• Best for discovery: Conceptual queries benefit most; exact identifier lookups should use grep
• Complements existing tools: Provides a faster initial signal, doesn't replace grep/explore

When the Plugin Helps Most

• Conceptual queries: "Where is the authentication logic?" (no keywords to grep for)
• Unfamiliar codebases: You don't know what to search for yet
• Large codebases: Semantic search scales better than exhaustive exploration

🛠️ How It Works

graph TD
    subgraph Indexing
    A[Source Code] -->|Tree-sitter| B[Semantic Chunks]
    B -->|Embedding Model| C[Vectors]
    C -->|uSearch| D[(Vector Store)]
    C -->|SQLite| G[(Embeddings DB)]
    B -->|BM25| E[(Inverted Index)]
    B -->|Branch Catalog| G
    end

    subgraph Searching
    Q[User Query] -->|Embedding Model| V[Query Vector]
    V -->|Cosine Similarity| D
    Q -->|BM25| E
    G -->|Branch Filter| F
    D --> F[Hybrid Fusion]
    E --> F
    F --> R[Ranked Results]
    end

• Parsing: We use tree-sitter to intelligently parse your code into meaningful blocks (functions, classes, interfaces). JSDoc comments and docstrings are automatically included with their associated code.
• Chunking: Large blocks are split with overlapping windows to preserve context across chunk boundaries.
• Embedding: These blocks are converted into vector representations using your configured AI provider.
• Storage: Embeddings are stored in SQLite (deduplicated by content hash) and vectors in usearch with F16 quantization for 50% memory savings. A branch catalog tracks which chunks exist on each branch.
• Hybrid Search: Combines semantic similarity (vectors) with BM25 keyword matching, filtered by current branch.

Performance characteristics:

• Incremental indexing: ~50ms check time — only re-embeds changed files
• Smart chunking: Understands code structure to keep functions whole, with overlap for context
• Native speed: Core logic written in Rust for maximum performance
• Memory efficient: F16 vector quantization reduces index size by 50%
• Branch-aware: Automatically tracks which chunks exist on each git branch

🌿 Branch-Aware Indexing

The plugin automatically detects git branches and optimizes indexing across branch switches.

How It Works

When you switch branches, code changes but embeddings for unchanged content remain the same. The plugin:

• Stores embeddings by content hash: Embeddings are deduplicated across branches
• Tracks branch membership: A lightweight catalog tracks which chunks exist on each branch
• Filters search results: Queries only return results relevant to the current branch

Benefits

Scenario	Without Branch Awareness	With Branch Awareness
Switch to feature branch	Re-index everything	Instant — reuse existing embeddings
Return to main	Re-index everything	Instant — catalog already exists
Search on branch	May return stale results	Only returns current branch's code

Automatic Behavior

• Branch detection: Automatically reads from .git/HEAD
• Re-indexing on switch: Triggers when you switch branches (via file watcher)
• Legacy migration: Automatically migrates old indexes on first run
• Garbage collection: Health check removes orphaned embeddings and chunks

Storage Structure

.opencode/index/
├── codebase.db           # SQLite: embeddings, chunks, branch catalog
├── vectors.usearch       # Vector index (uSearch)
├── inverted-index.json   # BM25 keyword index
└── file-hashes.json      # File change detection

🧰 Tools Available

The plugin exposes these tools to the OpenCode agent:

codebase_search

The primary tool. Searches code by describing behavior.

• Use for: Discovery, understanding flows, finding logic when you don't know the names.
• Example: "find the middleware that sanitizes input"

Writing good queries:

✅ Good queries (describe behavior)	❌ Bad queries (too vague)
"function that validates email format"	"email"
"error handling for failed API calls"	"error"
"middleware that checks authentication"	"auth middleware"
"code that calculates shipping costs"	"shipping"
"where user permissions are checked"	"permissions"

index_codebase

Manually trigger indexing.

• Use for: Forcing a re-index or checking stats.
• Parameters: force (rebuild all), estimateOnly (check costs), verbose (show skipped files and parse failures).

index_status

Checks if the index is ready and healthy.

index_health_check

Maintenance tool to remove stale entries from deleted files and orphaned embeddings/chunks from the database.

🎮 Slash Commands

The plugin automatically registers these slash commands:

Command	Description
/search <query>	Pure Semantic Search. Best for "How does X work?"
/find <query>	Hybrid Search. Combines semantic search + grep. Best for "Find usage of X".
/index	Update Index. Forces a refresh of the codebase index.

⚙️ Configuration

Zero-config by default (uses auto mode). Customize in .opencode/codebase-index.json:

{
  "embeddingProvider": "auto",
  "scope": "project",
  "indexing": {
    "autoIndex": false,
    "watchFiles": true,
    "maxFileSize": 1048576,
    "maxChunksPerFile": 100,
    "semanticOnly": false
  },
  "search": {
    "maxResults": 20,
    "minScore": 0.1,
    "hybridWeight": 0.5,
    "contextLines": 0
  }
}

Options Reference

Option	Default	Description
embeddingProvider	"auto"	Which AI to use: auto, github-copilot, openai, google, ollama
scope	"project"	project = index per repo, global = shared index across repos
indexing
autoIndex	false	Automatically index on plugin load
watchFiles	true	Re-index when files change
maxFileSize	1048576	Skip files larger than this (bytes). Default: 1MB
maxChunksPerFile	100	Maximum chunks to index per file (controls token costs for large files)
semanticOnly	false	When true, only index semantic nodes (functions, classes) and skip generic blocks
retries	3	Number of retry attempts for failed embedding API calls
retryDelayMs	1000	Delay between retries in milliseconds
search
maxResults	20	Maximum results to return
minScore	0.1	Minimum similarity score (0-1). Lower = more results
hybridWeight	0.5	Balance between keyword (1.0) and semantic (0.0) search
contextLines	0	Extra lines to include before/after each match

Embedding Providers

The plugin automatically detects available credentials in this order:

• GitHub Copilot (Free if you have it)
• OpenAI (Standard Embeddings)
• Google (Gemini Embeddings)
• Ollama (Local/Private - requires nomic-embed-text)

⚠️ Tradeoffs

Be aware of these characteristics:

Aspect	Reality
Search latency	~800-1000ms per query (embedding API call)
First index	Takes time depending on codebase size (e.g., ~30s for 500 chunks)
Requires API	Needs an embedding provider (Copilot, OpenAI, Google, or local Ollama)
Token costs	Uses embedding tokens (free with Copilot, minimal with others)
Best for	Discovery and exploration, not exhaustive matching

💻 Local Development

• Build:

  npm run build
  

• Register in Test Project (use file:// URL in opencode.json):

  {
    "plugin": [
      "file:///path/to/opencode-codebase-index"
    ]
  }
  

  This loads directly from your source directory, so changes take effect after rebuilding.

🤝 Contributing

• Fork the repository
• Create a feature branch: git checkout -b feature/my-feature
• Make your changes and add tests
• Run checks: npm run build && npm run test:run && npm run lint
• Commit: git commit -m "feat: add my feature"
• Push and open a pull request

CI will automatically run tests and type checking on your PR.

Project Structure

├── src/
│   ├── index.ts              # Plugin entry point
│   ├── config/               # Configuration schema
│   ├── embeddings/           # Provider detection and API calls
│   ├── indexer/              # Core indexing logic + inverted index
│   ├── git/                  # Git utilities (branch detection)
│   ├── tools/                # OpenCode tool definitions
│   ├── utils/                # File collection, cost estimation
│   ├── native/               # Rust native module wrapper
│   └── watcher/              # File/git change watcher
├── native/
│   └── src/                  # Rust: tree-sitter, usearch, xxhash, SQLite
├── tests/                    # Unit tests (vitest)
├── commands/                 # Slash command definitions
├── skill/                    # Agent skill guidance
└── .github/workflows/        # CI/CD (test, build, publish)

Native Module

The Rust native module handles performance-critical operations:

• tree-sitter: Language-aware code parsing with JSDoc/docstring extraction
• usearch: High-performance vector similarity search with F16 quantization
• SQLite: Persistent storage for embeddings, chunks, and branch catalog
• BM25 inverted index: Fast keyword search for hybrid retrieval
• xxhash: Fast content hashing for change detection

Rebuild with: npm run build:native (requires Rust toolchain)

License

MIT