Hermes for Excel

An agentic AI add-in for Microsoft Excel. Hermes doesn't just answer questions — it executes actions on your live workbook in a closed loop: it reads, writes, formats, charts, looks at the results, and iterates until the job is done.

Since v2.0.0 the add-in is fully native: a single VSTO add-in embeds the chat UI (WebView2), talks to the local Hermes Gateway, and executes every action through the Excel COM object model — no Caddy, no certificates, no manifest sideloading, no Office.js. One MSI installs everything.

Capabilities

Core (17 actions):

Category	What the agent can do
Read	read_range, read_sheet_names, read_table, read_selection
Write	write_range, write_formula, calculate (full workbook recalc)
Sheets	create_sheet, rename_sheet, delete_sheet
Format	format_range (bold/italic/fill/colors/sizes/number formats), auto_fit
Tables	create_table, add_table_row, sort_table
Charts	create_chart, configure_chart

Pro (full COM object model, 15 actions):

Category	What the agent can do
Equations	insert_equation — genuine native equations (OMML math zones) from linear syntax or LaTeX — editable in Excel's own equation editor
Analysis	create_pivot_table (real pivots with layout + consolidation functions), goal_seek, add_power_query (a real Power Query from your M code, materialized or connection-only)
Charts pro	configure_chart_pro (combo charts, secondary axis, trendlines with equation/R²), create_slicer (functional, on tables or pivots)
Reporting	export_pdf, page_setup (orientation, print area, fit-to-pages, margins…)
Protection	protect_sheet (granular allowances), protect_workbook (structure/windows)
Agent vision	capture_range — the agent literally sees your sheet (cells and shapes/equations) as an image and reasons about it
Escape hatches	execute_mso (any built-in Ribbon command), undo, evaluate (arbitrary Excel formulas)

Everything runs locally and in-process: no open ports, no tokens, no proxy — the only thing that leaves your machine is the LLM traffic from your own gateway.

Components

Piece	What it does	Required?
Hermes for Excel add-in (VSTO)	Chat taskpane (embedded WebView2 UI) + native gateway proxy + COM executor for all 32 actions	Yes
Hermes Gateway (hermes-agent)	The local agent runtime (LLM orchestration, SSE streaming) on http://localhost:8642	Yes

Platform: Windows desktop Excel (2016+ / Microsoft 365).

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Quick start (users)

Everything installs per-user — no admin rights needed.

0. Prerequisites

• Windows 10/11 with Excel 2016+ or Microsoft 365 desktop.

• The Hermes Gateway running locally — this is the hermes-agent product (separate project; install it per its own documentation). In its .env:

  API_SERVER_ENABLED=true
  API_SERVER_KEY=secret_testing_key   # choose your own; you'll enter it in the add-in (step 3)

  Start it — the API listens on http://localhost:8642.

• .NET Framework 4.8 (inbox on Windows 10/11).

• VSTO Runtime and the WebView2 Runtime — both are present on most Windows 11 machines; the MSI checks for them and tells you if either is missing.

1. Install the add-in

Run HermesExcel-2.0.0.msi from Releases. On the first Excel start afterwards you'll see "Microsoft Office Customization Installer — Publisher cannot be verified" → click Install. This prompt is expected for unsigned builds (see Roadmap); it appears only once.

2. Open Excel

The Hermes taskpane opens on the right — that's the whole UI. There is no manifest to sideload and no proxy to run.

3. Connect to the gateway

1. In the taskpane header, click the gear icon (Connection settings).
2. API key: the API_SERVER_KEY value from the gateway's .env (step 0).
3. Model (only if the gateway default fails): some Hermes versions default new API sessions to an unresolved hermes-agent alias and then fail with MODEL_NOT_FOUND. Set this to a real model ID from your gateway (e.g. moonshotai/kimi-k3) to force it.
4. Save & reconnect — the connection indicator (plug icon) shows a green dot. Without this key the gateway rejects requests with 403 Invalid gateway API key.

4. Verify

• The plug icon shows a green dot (hover it for gateway details) and the lightning icon is lit (the action executor is built in — hover for the action count).
• Try: "inserta la ecuación de Colebrook en B2"

Custom gateway address? The add-in defaults to http://localhost:8642. To point elsewhere, create %LOCALAPPDATA%\Hermes\Excel\settings.json:

{ "gatewayUrl": "http://other-host:8642" }

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Troubleshooting

• Taskpane doesn't load / shows an error label: check %LOCALAPPDATA%\Hermes\Excel\host.log — the add-in logs every failure there.
• Plug stays red: the gateway isn't running on localhost:8642 (or set a custom gatewayUrl as shown above).
• VSTO add-in issues (devs): see docs/vsto-addin-troubleshooting.md.

Roadmap

• Code signing (removes the VSTO trust prompt + SmartScreen) once the project has traction — OSS-friendly options (SignPath, Certum) first.
• Auto-update for the MSI.

Contributing

See CONTRIBUTING.md — full dev setup, architecture notes, and the VSTO load-failure field guide. Release history lives in CHANGELOG.md; to report a vulnerability use the private flow in SECURITY.md (never a public issue).

License

AGPL-3.0 — free for the community; any derivative work (even offered as a network service) must stay open under the same terms.