docx-scalpel 0.1.0a3

Anchor-addressed DOCX editing for LLM agents — a thin client over Docxodus' DocxSession.

docx-scalpel

Anchor-addressed DOCX editing for LLM agents — a thin client over Docxodus' DocxSession.

docx-scalpel exposes Docxodus' stateful DOCX editor over a long-running .NET subprocess (docxodus-pyhost). The session lives in the host's memory until you explicitly release it, so an LLM agent can issue dozens of small edits against one document without paying the OOXML parse + Unid annotation + projection cost on every call.

Status: Alpha. linux-x64 wheels ship with a bundled docxodus-pyhost; other RIDs require a dev clone of Docxodus until the wheel matrix is extended (tracked in RELEASING.md).

Installation

pip install docx-scalpel

linux-x64 today; pre-release tags ship as 0.1.0a*, so use --pre if you want to opt in:

pip install --pre docx-scalpel

Source installs (pip install of the sdist, or pip install -e . from a dev clone) don't include a bundled host. Set DOCXODUS_HOST=/path/to/docxodus-pyhost to point at one you built, or run dotnet build tools/python-host/pyhost.csproj inside a Docxodus monorepo clone — the locator auto-discovers it.

Quick start

from docx_scalpel import open_session, FormatOp, Position

with open("contract.docx", "rb") as f:
    docx_bytes = f.read()

with open_session(docx_bytes) as session:
    # Walk template placeholders and fill them. The picker returns a string to
    # replace, or None to skip. fill_placeholders handles reverse-offset
    # ordering, $-prefix preservation, and multi-pass nested-bracket convergence
    # in one call.
    result = session.fill_placeholders(lambda p: "filled value")
    print(f"filled {result.filled} placeholders in {result.passes} passes")

    # Add a heading after the first body paragraph.
    proj = session.project()
    first_p = next(
        t for t in proj.anchor_index.values()
        if t.kind in ("p", "h") and t.scope == "body"
    )
    session.insert_paragraph(first_p.id, Position.AFTER, "## Reviewed by counsel")

    # Bold the first 8 characters of that paragraph.
    session.apply_format_by_substring(first_p.id, "Reviewed", FormatOp(bold=True))

    new_bytes = session.save()

with open("filled.docx", "wb") as f:
    f.write(new_bytes)

The with block is the documented lifecycle path — it calls session.close() on the way out, which releases the session from the host's SessionRegistry. A __del__ finalizer is a fallback for forgotten sessions but should not be relied on; interpreter shutdown may skip it.

Why a subprocess?

DocxSession holds a parsed WordprocessingDocument, an AnchorIndex of Unid-stamped block-level targets, a cached MarkdownProjection, and a bounded UndoRing of per-part XDocument snapshots. Recreating it costs tens of ms on small docs and seconds on large ones. The subprocess model lets one Python process drive many sessions across many calls, all in one host's memory, until you decide to close them.

Architecture:

Python process                 docxodus-pyhost (.NET 8)
─────────────                  ──────────────────────────
DocxSession  ──NDJSON──>       Dispatcher
                               │
                               ▼
                               DocxSessionOps
                               │
                               ▼
                               SessionRegistry (handle → DocxSession)

One host per Python process. Many sessions inside the host. atexit sends shutdown and (if the host doesn't comply) terminates / kills.

Full design + wire-protocol spec: docs/architecture/python_docxodus.md. Delta-spec for the docx-scalpel rebrand: docs/superpowers/specs/2026-05-26-docx-scalpel-design.md.

Development

Build the host binary (one-time)

# From the Docxodus repo root:
dotnet build tools/python-host/pyhost.csproj -c Release

This produces tools/python-host/bin/Release/net8.0/docxodus-pyhost. _host_locator.py discovers it automatically when you pip install -e . from a monorepo clone.

For non-monorepo development, set DOCXODUS_HOST=/path/to/docxodus-pyhost to override the discovery path.

Editable install + tests

cd python
python -m venv .venv
.venv/bin/pip install -e .[test]
.venv/bin/pytest -v

Test layout

• tests/test_smoke.py — end-to-end mirror of Docxodus.Tests/DocxSessionSmokeTest.cs. v1 acceptance gate.
• tests/test_lifecycle.py — proves session persistence, idempotent close, singleton host, finalizer fallback.

Tests share the Docxodus monorepo's TestFiles/ corpus so divergence between Python and .NET on identical inputs is detectable.

API surface

The DocxSession class exposes every op in Docxodus.Internal.DocxSessionOps as a snake-case method:

Tier	Methods
Lifecycle	save, close, undo, redo
Projection	project, project_anchor
Discovery	grep, grep_cross_block, find_placeholders, find_by_text, find_all_by_text, find_by_regex, find_by_kind, find_by_annotation, find_by_label, find_by_bookmark, list_annotations, exists, get_anchor_info, get_anchor_infos, get_edit_summary, remaining_placeholders, get_diff
A: text mutations	replace_text, replace_text_range, replace_text_at_span, replace_inner, replace_match, delete_block, delete_range, delete_section
B: structural	insert_paragraph, split_paragraph, merge_paragraphs
C: formatting	apply_format, apply_format_by_substring, set_paragraph_style, set_list_level, remove_list_membership
D: tables	replace_cell_content
Raw XML	session.raw.get_xml, session.raw.insert_xml, session.raw.replace_xml

Every mutation method returns an EditResult envelope — transport-level failures raise DocxodusTransportError, but a business outcome (anchor_not_found, malformed_markdown, etc.) returns EditResult(success=False, error=EditError(...)). Never an exception across the API boundary.

License

MIT. Built on top of Docxodus, which is itself a fork of Open-Xml-PowerTools.