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: Beta. Wheels ship a bundled docxodus-pyhost for linux-x64, linux-arm64, osx-arm64, and win-x64; any other platform installs from the sdist and needs a host of its own (see below).

Installation

pip install docx-scalpel

That resolves a wheel on linux-x64, linux-arm64, osx-arm64, or win-x64 — each carrying a self-contained docxodus-pyhost built from the same commit as the release, so there's no .NET runtime to install and no version to pin.

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)

Atomic mutation batches

Use execute_batch when a plan spans several edits that must either all land or all disappear. Atomic is the default; success is one version/undo unit and failure returns the indexed operation error after restoring the complete package and history state:

from docx_scalpel import MutationBatchStep

result = session.execute_batch([
    MutationBatchStep("replace_text", {
        "anchorId": first_p.id,
        "markdown": "Replacement text",
    }),
    MutationBatchStep("set_header_text", {
        "anchorId": first_p.id,
        "kind": "default",
        "markdown": "Confidential",
    }),
])
if not result.success:
    print(result.failure.index, result.failure.action, result.failure.error)

Select MutationBatchMode.BEST_EFFORT explicitly only when retaining successful steps after another step fails is intended.

Isolated previews

preview_batch takes the same steps and predicts their outcome on a complete clone of the package. The live session is never a mutation target, so its bytes, version and undo/redo history are untouched whatever the steps do:

from docx_scalpel import MutationPreviewHtmlMode

preview = session.preview_batch(
    [
        MutationBatchStep("replace_text", {
            "anchorId": first_p.id,
            "markdown": "Proposed replacement",
        }),
    ],
    html_mode=MutationPreviewHtmlMode.FULL,
)
print(preview.html)
print(preview.revision_changes.added, preview.comment_changes.added, preview.warnings)

Both preview_batch and execute_batch return the enriched receipt: base_version, result_version, package_hash, {added, removed, modified} change sets for revisions, comments and annotations, and warnings. MutationPreviewHtmlMode.SCOPED renders one block and requires html_anchor_id. package_hash is None — never "" — when it could not be computed, so check it before using it as a replay assertion.

A step's operation is any mutating session operation, including the structural table ops (insert_table, insert_table_row, merge_cells, …); read-only operations, undo/redo, and session configuration are rejected as invalid_batch_step.

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 10)
─────────────                  ──────────────────────────
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/net10.0/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.

A dotnet build host is framework-dependent, so it needs the .NET 10 runtime at launch. If your system dotnet is older and .NET 10 lives elsewhere (e.g. ~/.dotnet), the host will exit with You must install or update .NET to run this application; export DOTNET_ROOT to point at the newer install. Released wheels are unaffected — they bundle a self-contained host with no runtime lookup.

export DOTNET_ROOT="$HOME/.dotnet"

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/test_table_addressing.py — canonical table identities, coordinate resolution, every table mutation, mappings, and anchor-stable reopen.

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:

Package verification is available statelessly as generate_package_manifest(docx_bytes) and for the current logical checkpoint as session.get_package_manifest(). Both return frozen typed dataclasses for the schema documented in package_manifests.md; validation failures are structured findings rather than editable-package exceptions. Closed wire vocabularies decode to str enums, and decimal-string ZIP64 sizes decode to exact Python int values.

The default delivery gate is likewise available as verify_deliverable(docx_bytes, baseline=None) and session.verify_deliverable(). Both return a typed DeliverableVerificationResult. The stateless form binds the report to the exact supplied bytes; the session form verifies its clean-save checkpoint and, with the default initial capture, compares it with the exact opening bytes.

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.

PageMap accepts physical pagination materialized by an external renderer. Registration requires the session's exact document version and validates the renderer fingerprint, page/section order, canonical anchors, geometry, story, table ownership, and fragment order. Pass the same PageCitationRequest to search/scoped reads to attach citations. Continuous/no-map and stale layouts return typed unavailable results; the client never guesses page numbers. See the portable PageMap contract.

For optimistic concurrency, build a MutationPreconditions object and use session.check_preconditions(...) for a read-only probe or with session.preconditioned(guards): ... to attach it to each mutation request in the block. The guard can require the document version, anchor hash/exact visible text or range/kind/scope, and an exact replacement match count. A mismatch returns EditErrorCode.PRECONDITION_FAILED with structured expected/actual/current target metadata and leaves bytes, version, and undo history unchanged.

Stateless functions

Alongside the session API, the package exposes stateless one-shot functions at the module root — no session handle, they take DOCX bytes in and return bytes / data out:

The docx_diff_* family is a thin client over Docxodus' DocxDiff IR diff engine. Tune pairwise comparisons with DocxDiffSettings and N-way consolidation with DocxDiffConsolidateSettings (whose conflict_resolution takes a ConflictResolution value). DetectMoves/format-change tracking, header/footer comparison, and per-reviewer attribution all round-trip through these calls.

For an open session, session.get_semantic_changes() compares the exact opening package with the current logical checkpoint. It requires the default DocxSessionSettings(capture_initial_projection=True). The schema and package-suppression rules are documented in semantic_diff.md.

from docx_scalpel import docx_diff_compare, docx_diff_get_revisions, DocxDiffSettings

with open("v1.docx", "rb") as f: left = f.read()
with open("v2.docx", "rb") as f: right = f.read()

redline = docx_diff_compare(left, right, DocxDiffSettings(author_for_revisions="Reviewer"))
for rev in docx_diff_get_revisions(left, right):
    print(rev.type, rev.text)

Portable history files

open_history_archive(bytes) opens a standalone readonly history. history.document(id) binds version controls; history.import_history_archive(bytes) resumes exact history in host-owned storage. See the short usage guide and real archives. No transport or autosave is added.

License

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