AFT — Agent File Toolkit

Tree-sitter powered code analysis tools for AI coding agents.

AFT replaces generic read/write file operations with semantic, symbol-level tools that give agents precise control over code — without the token waste of reading full files or the fragility of line-number edits.

---

What is AFT?

AI coding agents are fast, but their interaction with code is often blunt. The typical pattern: read an entire file to find one function, construct a diff from memory, apply it by line number, and hope nothing shifted. Tokens burned on context noise. Edits that break when the file changes. Navigation that requires reading three files to answer "what calls this?"

AFT is a toolkit built on top of tree-sitter's concrete syntax trees. Every operation addresses code by what it is — a function, a class, a call site, a symbol — not by where it happens to sit in a file right now. Agents can outline a file's structure in one call, zoom into a single function, edit it by name, then follow its callers across the workspace. All without reading a single line they don't need.

Starting with v0.3.0, AFT hoists itself into opencode's built-in tool slots. The read, write, edit, apply_patch, ast_grep_search, ast_grep_replace, and lsp_diagnostics tools are replaced by AFT-enhanced versions — same names the agent already knows, but now backed by the Rust binary for backups, formatting, inline diagnostics, and symbol-aware operations.

The toolkit is a two-component system: a Rust binary that does the heavy lifting (parsing, analysis, edits, formatting) and a TypeScript plugin that integrates with OpenCode. The binary ships pre-built for all major platforms and downloads automatically on first use — no install ceremony required.

---

How it Helps Agents

The token problem. A 500-line file costs ~375 tokens to read. Most of the time, the agent needs one function. aft_zoom with a symbol param returns that function plus a few lines of context: ~40 tokens. Over a multi-step task, the savings compound fast.

The fragile-edit problem. Line-number edits break the moment anything above the target moves. edit in symbol mode addresses the function by name. The agent writes the new body; AFT finds the symbol, replaces it, validates syntax, and runs the formatter. Nothing to count.

The navigation problem. "Where is this function called?" means grep or reading every importer. aft_navigate with callers mode returns every call site across the workspace in one round trip. impact mode goes further: it tells the agent what else breaks if that function's signature changes.

---

Features

• File read — line-numbered file content, directory listing, and image/PDF detection
• Semantic outline — list all symbols in a file (or several files at once) with kind, name, line range, visibility
• Symbol editing — replace a named symbol by name with auto-format and syntax validation
• Match editing — find-and-replace by content with fuzzy fallback (4-pass: exact → trim trailing → trim both → normalize Unicode)
• Batch & transaction edits — atomic multi-edit within a file, or atomic multi-file edits with rollback
• Glob replace — pattern replace across all matching files in one call
• Patch apply — multi-file *** Begin Patch format for creates, updates, deletes, and moves
• Call tree & callers — forward call graph and reverse lookup across the workspace
• Trace-to & impact analysis — how does execution reach this function? what breaks if it changes?
• Data flow tracing — follow a value through assignments and parameters across files
• Auto-format & auto-backup — every edit formats the file and saves a snapshot for undo
• Import management — add, remove, organize imports language-aware (TS/JS/TSX/Python/Rust/Go)
• Structural transforms — add class members, Rust derive macros, Python decorators, Go struct tags, wrap try/catch
• Workspace-wide refactoring — move symbols between files (updates all imports), extract functions, inline functions
• Safety & recovery — undo last edit, named checkpoints, restore to any checkpoint
• AST pattern search & replace — structural code search using meta-variables ($VAR, $$$), powered by ast-grep
• Inline diagnostics — write and edit return LSP errors detected after the change
• UI metadata — the OpenCode desktop shows file paths and diff previews (+N/-N) for every edit
• Local tool discovery — finds biome, prettier, tsc, pyright in node_modules/.bin automatically

---

How to Use

OpenCode

Add AFT to your OpenCode config:

// ~/.config/opencode/config.json
{
  "plugins": ["@cortexkit/aft-opencode"]
}

That's it. On the next session start, the binary downloads if needed and all tools become available. AFT replaces opencode's built-in read, write, edit, apply_patch, ast_grep_search, ast_grep_replace, and lsp_diagnostics with enhanced versions — all powered natively by AFT — plus adds the aft_ family of semantic tools on top.

Here's a typical agent workflow:

1. Get the file structure:

// aft_outline
{ "filePath": "src/auth/session.ts" }

// response
{
  "symbols": [
    { "kind": "function", "name": "createSession", "line_start": 12, "line_end": 34, "visibility": "export" },
    { "kind": "function", "name": "validateToken", "line_start": 36, "line_end": 58, "visibility": "export" },
    { "kind": "interface", "name": "SessionOptions", "line_start": 1, "line_end": 10, "visibility": "export" }
  ]
}

2. Read the specific function:

// aft_zoom
{ "filePath": "src/auth/session.ts", "symbol": "validateToken" }

3. Edit it by name:

// edit
{
  "filePath": "src/auth/session.ts",
  "symbol": "validateToken",
  "content": "export function validateToken(token: string): boolean {\n  if (!token) return false;\n  return verifyJwt(token);\n}"
}

4. Check who calls it before changing its signature:

// aft_navigate
{ "op": "callers", "filePath": "src/auth/session.ts", "symbol": "validateToken", "depth": 2 }

---

Tool Reference

All line numbers are 1-based (matching editor, git, and compiler conventions). Line 1 is the first line of the file.

Hoisted tools

These replace opencode's built-ins. Registered under the same names by default. When hoist_builtin_tools: false, they get the aft_ prefix instead (e.g. aft_read).

Tool	Replaces	Description	Key Params
read	opencode read	File read, directory listing, image/PDF detection	filePath, startLine, endLine, offset, limit
write	opencode write	Write file with auto-dirs, backup, format, inline diagnostics	filePath, content
edit	opencode edit	Find/replace, symbol replace, batch, transaction, glob	filePath, oldString, newString, symbol, content, edits[]
apply_patch	opencode apply_patch	*** Begin Patch multi-file patch format	patchText
ast_grep_search	opencode ast_grep_search	AST pattern search with meta-variables	pattern, lang, paths[], globs[]
ast_grep_replace	opencode ast_grep_replace	AST pattern replace (applies by default)	pattern, rewrite, lang, dryRun
lsp_diagnostics	opencode lsp_diagnostics	Errors/warnings from language server	filePath, directory, severity, waitMs

AFT-only tools

Always registered with aft_ prefix regardless of hoisting setting.

Tool	Description	Key Params
aft_outline	Structural outline of a file, files, or directory	filePath, files[], directory
aft_zoom	Inspect symbols with call-graph annotations	filePath, symbol, symbols[], startLine, endLine
aft_delete	Delete a file with backup	filePath
aft_move	Move or rename a file with backup	filePath, destination
aft_navigate	Call graph and data-flow navigation	op, filePath, symbol, depth
aft_import	Language-aware import add/remove/organize	op, filePath, module, names[]
aft_transform	Structural code transforms (members, derives, decorators)	op, filePath, container, target
aft_refactor	Workspace-wide move, extract, inline	op, filePath, symbol, destination
aft_safety	Undo, history, checkpoints, restore	op, filePath, name

---

read

Plain file reading and directory listing. Pass filePath to read a file, or a directory path to list its entries. Paginate large files with start_line/end_line or offset/limit.

// Read full file
{ "filePath": "src/app.ts" }

// Read lines 50-100
{ "filePath": "src/app.ts", "startLine": 50, "endLine": 100 }

// Read 30 lines from line 200
{ "filePath": "src/app.ts", "offset": 200, "limit": 30 }

// List directory
{ "filePath": "src/" }

Returns line-numbered content (e.g. 1: const x = 1). Directories return sorted entries with trailing / for subdirectories. Binary files return a size-only message. Image and PDF files return metadata suitable for UI preview. Output is capped at 50KB.

For symbol inspection with call-graph annotations, use aft_zoom.

---

write

Write the full content of a file. Creates the file (and any missing parent directories) if it doesn't exist. Backs up any existing content before overwriting.

{ "filePath": "src/config.ts", "content": "export const TIMEOUT = 10000;\n" }

Returns inline LSP diagnostics if type errors are introduced. Auto-formats using the project's configured formatter (biome, prettier, etc.).

For partial edits (find/replace), use edit instead.

---

edit

The main editing tool. Mode is determined by which parameters you pass:

Find and replace — pass filePath + oldString + newString:

{ "filePath": "src/config.ts", "oldString": "const TIMEOUT = 5000", "newString": "const TIMEOUT = 10000" }

Matching uses a 4-pass fuzzy fallback: exact match first, then trailing-whitespace trim, then both-ends trim, then Unicode normalization. Returns an error if multiple matches exist — use occurrence: N (0-indexed) to pick one, or replaceAll: true to replace all.

Symbol replace — pass filePath + symbol + content:

{
  "filePath": "src/utils.ts",
  "symbol": "formatDate",
  "content": "export function formatDate(d: Date): string {\n  return d.toISOString().split('T')[0];\n}"
}

Includes decorators, doc comments, and attributes in the replacement range.

Batch edits — pass filePath + edits array. Atomic: all edits apply or none do.

{
  "filePath": "src/constants.ts",
  "edits": [
    { "oldString": "VERSION = '1.0'", "newString": "VERSION = '2.0'" },
    { "line_start": 5, "line_end": 7, "content": "// updated header\n" }
  ]
}

Set content to "" to delete lines. Per-edit occurrence is supported.

Multi-file transaction — pass operations array. Rolls back all files if any operation fails.

{
  "operations": [
    { "file": "a.ts", "command": "write", "content": "..." },
    { "file": "b.ts", "command": "edit_match", "match": "x", "replacement": "y" }
  ]
}

Glob replace — use a glob as filePath with replaceAll: true:

{ "filePath": "src/**/*.ts", "oldString": "oldName", "newString": "newName", "replaceAll": true }

All modes support dryRun: true to preview as a diff without modifying files. LSP diagnostics are returned automatically after every edit (unless dryRun is set) — if type errors are introduced, they appear inline in the response.

---

apply_patch

Apply a multi-file patch using the *** Begin Patch format. Creates, updates, deletes, and renames files atomically — if any operation fails, all revert.

*** Begin Patch
*** Add File: path/to/new-file.ts
+line 1
+line 2
*** Update File: path/to/existing-file.ts
@@ context anchor line
-old line
+new line
*** Delete File: path/to/obsolete-file.ts
*** End Patch

Context anchors (@@) use fuzzy matching to handle whitespace and Unicode differences. Returns LSP diagnostics inline for any updated files that introduce type errors.

---

ast_grep_search

Search for structural code patterns using meta-variables. Patterns must be complete AST nodes.

{ "pattern": "console.log($MSG)", "lang": "typescript" }

• $VAR matches a single AST node
• $$$ matches multiple nodes (variadic)

Returns matches with file, line (1-based), column, matched text, and captured variable values. Add context: 3 to include surrounding lines.

// Find all async functions in JS/TS
{ "pattern": "async function $NAME($$$) { $$$ }", "lang": "typescript" }

---

ast_grep_replace

Replace structural code patterns across files. Applies changes by default — set dryRun: true to preview.

{ "pattern": "console.log($MSG)", "rewrite": "logger.info($MSG)", "lang": "typescript" }

Meta-variables captured in pattern are available in rewrite. Returns unified diffs per file in dry-run mode, or writes changes with backups when applied.

---

lsp_diagnostics

Get errors, warnings, and hints from the language server. Lazily spawns the appropriate server (typescript-language-server, pyright, rust-analyzer, gopls) on first use.

// Check a single file
{ "filePath": "src/api.ts", "severity": "error" }

// Check all files in a directory
{ "directory": "src/", "severity": "all" }

// Wait for fresh diagnostics after an edit
{ "filePath": "src/api.ts", "waitMs": 2000 }

Returns { file, line, column, severity, message, code } per diagnostic.

---

aft_outline

Returns all top-level symbols in a file with their kind, name, line range, visibility, and nested members (methods in classes, sub-headings in Markdown). Accepts a single filePath, a files array, or a directory to outline all source files recursively.

For Markdown files (.md, .mdx): returns heading hierarchy with section ranges — each heading becomes a symbol you can read by name.

// Outline two files at once
{ "files": ["src/server.ts", "src/router.ts"] }

// Outline all source files in a directory
{ "directory": "src/auth" }

---

aft_zoom

Inspect code symbols with call-graph annotations. Returns the full source of named symbols with calls_out (what it calls) and called_by (what calls it) annotations.

Use this when you need to understand a specific function, class, or type in detail — not for reading entire files (use read for that). Also supports line-range reads with context.

// Inspect a single symbol
{ "filePath": "src/app.ts", "symbol": "handleRequest" }

// Inspect multiple symbols in one call
{ "filePath": "src/app.ts", "symbols": ["Config", "createApp"] }

// Read a line range with context
{ "filePath": "src/app.ts", "startLine": 50, "endLine": 100 }

For Markdown files, use the heading text as the symbol name (e.g. "symbol": "Architecture").

---

aft_delete

Delete a file with an in-memory backup. The backup survives for the session and can be restored via aft_safety.

{ "filePath": "src/deprecated/old-utils.ts" }

Returns { file, deleted, backup_id } on success.

---

aft_move

Move or rename a file. Creates parent directories for the destination automatically. Falls back to copy+delete for cross-filesystem moves. Backs up the original before moving.

{ "filePath": "src/helpers.ts", "destination": "src/utils/helpers.ts" }

Returns { file, destination, moved, backup_id } on success.

---

aft_navigate

Call graph and data-flow analysis across the workspace.

Mode	What it does
call_tree	What does this function call? (forward, default depth 5)
callers	Where is this function called from? (reverse, default depth 1)
trace_to	How does execution reach this function from entry points?
impact	What callers are affected if this function changes?
trace_data	Follow a value through assignments and parameters. Needs expression.

// Find everything that would break if processPayment changes
{
  "op": "impact",
  "filePath": "src/payments/processor.ts",
  "symbol": "processPayment",
  "depth": 3
}

---

aft_import

Language-aware import management for TS, JS, TSX, Python, Rust, and Go.

// Add named imports with auto-grouping and deduplication
{
  "op": "add",
  "filePath": "src/api.ts",
  "module": "react",
  "names": ["useState", "useEffect"]
}

// Remove a single named import
{ "op": "remove", "filePath": "src/api.ts", "module": "react", "name": "useEffect" }

// Re-sort and deduplicate all imports by language convention
{ "op": "organize", "filePath": "src/api.ts" }

---

aft_transform

Scope-aware structural transformations that handle indentation correctly.

Op	Description
add_member	Insert a method or field into a class, struct, or impl block
add_derive	Add Rust derive macros (deduplicates)
wrap_try_catch	Wrap a TS/JS function body in try/catch
add_decorator	Add a Python decorator to a function or class
add_struct_tags	Add or update Go struct field tags

// Add a method to a TypeScript class
{
  "op": "add_member",
  "filePath": "src/user.ts",
  "container": "UserService",
  "code": "async deleteUser(id: string): Promise<void> {\n  await this.db.users.delete(id);\n}",
  "position": "last"
}

All ops support dryRun and validate ("syntax" or "full").

---

aft_refactor

Workspace-wide refactoring that updates imports and references across all files.

Op	Description
move	Move a symbol to another file, updating all imports workspace-wide
extract	Extract a line range (1-based) into a new function (auto-detects parameters)
inline	Replace a call site (1-based callSiteLine) with the function's body

// Move a utility function to a shared module
{
  "op": "move",
  "filePath": "src/pages/home.ts",
  "symbol": "formatCurrency",
  "destination": "src/utils/format.ts"
}

move saves a checkpoint before mutating anything. Use dryRun: true to preview as a diff.

---

aft_safety

Backup and recovery for risky edits.

Op	Description
undo	Undo the last edit to a file
history	List all edit snapshots for a file
checkpoint	Save a named snapshot of tracked files
restore	Restore files to a named checkpoint
list	List all available checkpoints

// Checkpoint before a multi-file refactor
{ "op": "checkpoint", "name": "before-auth-refactor" }

// Restore if something goes wrong
{ "op": "restore", "name": "before-auth-refactor" }

Note: Backups are held in-memory for the session lifetime (lost on restart). Per-file undo stack is capped at 20 entries — oldest snapshots are evicted when exceeded.

---

Configuration

AFT uses a two-level config system: user-level defaults plus project-level overrides. Both files are JSONC (comments allowed).

User config — applies to all projects:

~/.config/opencode/aft.jsonc

Project config — overrides user config for a specific project:

.opencode/aft.jsonc

Config Options

{
  // Replace opencode's built-in read/write/edit/apply_patch and oh-my-opencode's
  // ast_grep_search/ast_grep_replace/lsp_diagnostics with AFT-enhanced versions.
  // Default: true. Set to false to use aft_ prefix on all tools instead.
  "hoist_builtin_tools": true,

  // Auto-format files after every edit. Default: true
  "format_on_edit": true,

  // Auto-validate after edits: "syntax" (tree-sitter, fast) or "full" (runs type checker)
  "validate_on_edit": "syntax",

  // Per-language formatter overrides (auto-detected from project config files if omitted)
  // Keys: "typescript", "python", "rust", "go"
  // Values: "biome" | "prettier" | "deno" | "ruff" | "black" | "rustfmt" | "goimports" | "gofmt" | "none"
  "formatter": {
    "typescript": "biome",
    "rust": "rustfmt"
  },

  // Per-language type checker overrides (auto-detected if omitted)
  // Keys: "typescript", "python", "rust", "go"
  // Values: "tsc" | "biome" | "pyright" | "ruff" | "cargo" | "go" | "staticcheck" | "none"
  "checker": {
    "typescript": "biome"
  },

  // List of tool names to disable (e.g. ["aft_transform", "aft_refactor"])
  "disabled_tools": []
}

AFT auto-detects the formatter and checker from project config files (biome.json → biome, .prettierrc → prettier, Cargo.toml → rustfmt, pyproject.toml → ruff/black, go.mod → goimports). Local tool binaries (biome, prettier, tsc, pyright) are discovered in node_modules/.bin before falling back to the system PATH. You only need per-language overrides if auto-detection picks the wrong tool or you want to pin a specific formatter.

---

Architecture

AFT is two components that talk over JSON-over-stdio:

OpenCode agent
     |
     | tool calls
     v
@cortexkit/aft-opencode (TypeScript plugin)
  - Hoists enhanced read/write/edit/apply_patch/ast_grep_*/lsp_diagnostics
  - Registers aft_outline/navigate/import/transform/refactor/safety/delete/move
  - Manages a BridgePool (one aft process per project directory)
  - Resolves the binary path (cache → npm → PATH → cargo → download)
     |
     | JSON-over-stdio (newline-delimited)
     v
aft binary (Rust)
  - tree-sitter parsing (6 language grammars)
  - Symbol resolution, call graph, diff generation
  - Format-on-edit (shells out to biome / rustfmt / etc.)
  - Backup/checkpoint management
  - ~7 MB, zero runtime dependencies

The binary speaks a simple request/response protocol: the plugin writes a JSON object to stdin, the binary writes a JSON object to stdout. One process per working directory stays alive for the session — warm parse trees, no re-spawn overhead per call.

---

Supported Languages

Language	Outline	Edit	Imports	Refactor
TypeScript	✓	✓	✓	✓
JavaScript	✓	✓	✓	✓
TSX	✓	✓	✓	✓
Python	✓	✓	✓	✓
Rust	✓	✓	✓	partial
Go	✓	✓	✓	partial
Markdown	✓	✓	—	—

---

Development

AFT is a monorepo: bun workspaces for TypeScript, cargo workspace for Rust.

Requirements: Bun ≥ 1.0, Rust stable toolchain (1.80+).

# Install JS dependencies
bun install

# Build the Rust binary
cargo build --release

# Build the TypeScript plugin
bun run build

# Run all tests
bun run test        # TypeScript tests
cargo test          # Rust tests

# Lint and format
bun run lint        # biome check
bun run lint:fix    # biome check --write
bun run format      # biome format + cargo fmt

Project layout:

opencode-aft/
├── crates/
│   └── aft/              # Rust binary (tree-sitter core)
│       └── src/
├── packages/
│   ├── opencode-plugin/  # TypeScript OpenCode plugin (@cortexkit/aft-opencode)
│   │   └── src/
│   │       ├── tools/    # One file per tool group
│   │       ├── config.ts # Config loading and schema
│   │       └── downloader.ts
│   └── npm/              # Platform-specific binary packages
└── scripts/
    └── version-sync.mjs  # Keeps npm and cargo versions in sync

---

Roadmap

• C/C++ language support
• LSP integration for type-aware symbol resolution (partially implemented)
• Streaming responses for large call trees
• Watch mode for live outline updates

---

Contributing

Bug reports and pull requests are welcome. For larger changes, open an issue first to discuss the approach.

The binary protocol is documented in crates/aft/src/main.rs. Adding a new command means implementing it in Rust and adding a corresponding tool definition (or extending an existing one) in packages/opencode-plugin/src/tools/.

Run bun run format and cargo fmt before submitting. The CI will reject unformatted code.

---

License

MIT