Each tool targets a distinct resource and action: vendor search, PO listing, single PO retrieval, and invoice posting. There is no overlap between listing purchase orders and getting one order, since one is scoped per-vendor and the other per-document.

All four names follow a strict verb_noun snake_case pattern (search_vendors, list_purchase_orders, get_purchase_order, post_vendor_invoice). Verbs are well chosen and consistently distinguish read vs. write operations.

Four tools is on the lean side but each supports a step in the vendor-invoice workflow, so nothing is redundant. A slightly broader surface (e.g. retrieving posted invoices) would make the set feel less minimal.

The core workflow — find vendor, inspect open PO amounts, read a PO, then post/preview an invoice — is fully covered, including idempotency. Minor gaps remain: no way to list or fetch invoices by vendor/reference outside of a repeat post, and no vendor-detail retrieval.