Arezzo

Deterministic compiler for Google Docs API operations.

You cannot safely modify a Google Doc by constructing batchUpdate requests yourself. The API uses UTF-16 code units with cascading index shifts — insert 10 characters at position 50, and every subsequent index in your batch is now wrong. A single miscalculation silently corrupts the document with no error message.

Arezzo compiles semantic intent into a correct request sequence. Tell it what you want to do; it handles the index arithmetic.

For AI agents (MCP tools)

Arezzo exposes three tools via the Model Context Protocol:

read_document(document_id)
  → Returns the document's structural map: headings with hierarchy,
    named ranges, tables, section boundaries. Call this before editing
    so you know what addresses are available.

edit_document(document_id, operations)
  → Compiles operations into correct batchUpdate requests and executes
    them. Handles UTF-16 arithmetic, cascading index shifts, and
    OT-compatible request ordering. Supported operations: insert/delete/
    replace text, formatting (bold, italic, headings, links), tables,
    lists, images, headers/footers, footnotes, named ranges.

validate_operations(document_id, operations)
  → Compile-only dry run. Returns the compiled requests for inspection
    without executing. Use before edit_document when uncertain.

Operation format

{
  "type": "insert_text",
  "address": {"heading": "Revenue Analysis"},
  "params": {"text": "New paragraph content.\n"}
}

Address modes:

• {"heading": "Section Name"} — by heading text
• {"named_range": "range_name"} — by named range
• {"bookmark": "bookmark_id"} — by bookmark ID
• {"start": true} — document start
• {"end": true} — document end
• {"index": 42} — absolute UTF-16 index

Operation types: insert_text, delete_content, replace_all_text, replace_section, update_text_style, update_paragraph_style, insert_bullet_list, insert_table, insert_table_row, insert_table_column, delete_table_row, delete_table_column, insert_image, create_header, create_footer, create_footnote, create_named_range, replace_named_range_content, insert_page_break

Recommended workflow

read_document → edit_document → (if structural changes) read_document → edit_document

Always read before editing. After inserting structural elements (tables, headers, footers), read again to get the new element indices before adding content inside them.

Installation

pip install arezzo
arezzo init

arezzo init walks through Google OAuth setup and writes platform config files for your MCP client.

Setup

Prerequisites: A Google Cloud project with the Google Docs API enabled and an OAuth 2.0 client ID (Desktop application type).

arezzo init

The wizard:

1. Copies your credentials.json to ~/.config/arezzo/
2. Runs the OAuth consent flow (browser opens once)
3. Generates config files for Claude Code, Cursor, and VS Code

For Claude Desktop, arezzo init prints the config block to add manually.

Platform configs

After arezzo init, config files are written to your project directory:

Claude Code / Cursor (.mcp.json):

{
  "mcpServers": {
    "arezzo": {
      "command": "arezzo"
    }
  }
}

VS Code (.vscode/mcp.json):

{
  "servers": {
    "arezzo": {
      "type": "stdio",
      "command": "arezzo"
    }
  }
}

Claude Desktop (~/Library/Application Support/Claude/claude_desktop_config.json on macOS):

{
  "mcpServers": {
    "arezzo": {
      "command": "arezzo"
    }
  }
}

Why Arezzo exists

The Google Docs batchUpdate API operates on UTF-16 code units with absolute index positions. Every character insertion or deletion shifts all subsequent indices. In a batch with multiple mutations, each request's indices must account for the effect of every prior request in the same batch.

Getting this right requires:

• UTF-16 length calculation (not Python len() — surrogate pairs count differently)
• Reverse-order execution for same-type mutations (delete from end to start)
• Two-phase compilation (content mutations before format mutations)
• Cascading offset tracking across multi-step operations

Arezzo handles this deterministically. The same input always produces the same output. No reasoning, no guessing, no "usually works."

Architecture

semantic operation
    ↓
arezzo.parser.parse_document()    — build heading/range/bookmark indexes
    ↓
arezzo.address.resolve_address()  — semantic reference → document index
    ↓
arezzo.operations.*               — operation → batchUpdate request(s)
    ↓
arezzo.index.sort_requests()      — OT-compatible mutation ordering
    ↓
correct batchUpdate request sequence

The engine is a pure function: compile_operations(doc, operations) → requests. Deterministic. No side effects. No API calls.

The MCP server (arezzo.server) wraps the engine with Google Docs API I/O and behavioral guidance fields (next_step, present_to_user, document_reality).

License

MIT — Convergent Methods, LLC