Authenticate with your TaxJar API token in the Authorization header as 'Token token=<API_KEY>'
POST to https://api.taxjar.com/v2/taxes with a JSON body containing 'from_country', 'from_zip', 'from_state', 'to_country', 'to_zip', 'to_state', 'amount', and 'shipping'
Include a 'line_items' array with 'id', 'quantity', 'unit_price', and optionally 'product_tax_code' for each item to get per-line breakdowns
Read 'tax.amount_to_collect' from the response for the total tax due and 'tax.breakdown' for jurisdiction-level detail
Store the returned 'tax.rate' and jurisdiction data alongside the order record for audit purposes
Known gotchas
Omitting 'product_tax_code' causes TaxJar to default to fully taxable tangible personal property; digital goods, groceries, and clothing may have different rates
Sandbox and production use different base URLs (api.sandbox.taxjar.com vs api.taxjar.com); sandbox tokens do not work on production
TaxJar returns 0 tax for transactions where the seller has no nexus in the destination state, even if the buyer's state has a tax; always separately track your nexus registrations
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp