Automating invoices with agents

facturium's builder uses plain HTML form controls, and its state persists locally in the browser's IndexedDB — no hidden server-side session — which makes it straightforward for a Playwright-class browser agent to drive directly, today, before any dedicated scripting API exists.

Every control in the builder carries a stable data-testid attribute, the same ones this site's own tests use, so they won't shift between releases without notice:

• Business settings (open settings-open first — these controls mount inside the settings sheet and aren't in the page until it's open): biz-name, biz-address, biz-tax-id, biz-email, biz-phone, logo-input, logo-remove (conditional — only appears once a logo has been set), number-prefix, default-currency, default-tax-bps, accent-color, footer-toggle, paper-size, backup-export, backup-import, settings-close.
• Client: client-pick, client-name, client-address, client-email, client-save.
• Line items: item-row, item-desc-<n>, item-qty-<n>, item-unit-<n>, item-rate-<n>, item-remove-<n>, item-add.
• Rates: currency-select, tax-bps, discount-kind, discount-value (conditional — only appears once discount-kind is changed away from "none").
• Invoice details: issue-date, due-mode, due-date (conditional — only appears once due-mode is set to "date"), invoice-number, po-ref, payment-text, notes-text, terms-text.
• Actions: new-invoice, save-invoice, download-pdf, print-invoice.
• Saved lists: invoice-list, invoice-row, mark-sent, mark-paid, duplicate-invoice, delete-invoice, client-list.

On a cold load, an agent should open settings first (settings-open) and fill the business fields, then close it and fill client-name and the first line item (item-desc-0, item-qty-0, item-rate-0). It can read the totals bar (totals-bar) and preview pane (preview-pane) to confirm the numbers, click save-invoice, and then download-pdf to trigger a real browser download — the same sequence a person would use, described step by step in how to create an invoice. The UI is localized; set an English locale (via the language switcher or a browser language preference) if you want the English label set above to match what you see.

A versioned, in-page scripting API — window.facturium.v1 — is available today. A page.evaluate()-style agent (Playwright, Puppeteer) can call methods like newInvoice(), setClient(), addItem(), saveInvoice(), and exportPdf() directly, instead of driving form controls one field at a time. It's local-only and frozen (account/sync verbs are a v2 concern and will never be added), built on the same validators the form fields use, and a mutation is visible to an immediately following getState() call in the same tick. exportPdf()/exportData() return their bytes on this window facade only — nothing document- or logo-shaped ever appears in a WebMCP tool result. See the Scripting API section of /llms.txt for the full method table, error codes, and a Playwright example.

Metadata-only WebMCP tools are also available via document.modelContext: facturium_get_capabilities (registered on every page, not just the builder), and, scoped to the builder, facturium_new_invoice, facturium_add_item, facturium_set_client, and facturium_export_download (triggers a real local download and returns only { ok, fileName, byteLength }).

This site publishes /llms.txt with an Automation section (the testids above) and a Scripting API section (the window.facturium.v1 method table), kept in sync with the real controls and the real contract, and an /agents.json manifest describing both interfaces as available.