Contractor Onboarding & W-9 Intake: No More January Tax-Doc Scramble
Send contractors a secure intake link, collect a complete W-9 and classification answers, validate the TIN, and let finance approve each one as payable — so a contractor can't be paid until their tax record is clean and signed off.
A web tool where you send a contractor a secure intake link, they submit their W-9 (legal name, TIN, entity type, address) and classification answers, the tool validates the TIN format and entity consistency, finance reviews and approves each onboarding, and only then does the contractor become a payable vendor — with the W-9 encrypted at rest and an approved-vendor CSV ready for your AP system.
Before you start
- A Supabase account (free)
- A Vercel account (free)
- A Resend account (free)
- Your current vendor/contractor list (optional, for import)
- Your accounting/AP system's vendor-import column layout
- Claude Code or any AI coding agent
The problem this kills
You bring on a new contractor, they do the work, they send an invoice — and only then does someone in finance realize you never got a clean W-9. Now you're chasing a busy person for their legal name, their tax ID, and their entity type while their payment sits in limbo. Multiply that by every contractor you onboarded all year and you get the January scramble: hunting down missing TINs, guessing whether someone is a sole proprietor or an LLC, and discovering a transposed digit only when the IRS sends a B-notice.
The root problem is timing. Tax data gets collected after the relationship starts, when you have the least leverage and the most urgency. You don't need to live like this, and you don't need to be a developer to fix it. Collect a complete, validated W-9 before the first dollar goes out, and year-end becomes a non-event.
What you'll build
A simple internal web tool plus a secure contractor-facing intake form. Finance sends a new contractor a one-time secure intake link. The contractor fills in their W-9 details — legal name, any business/DBA name, their TIN (their EIN or SSN), entity type, and address — and answers a short set of classification questions about how they work with you. The tool validates the submission on the spot: the TIN is the right length and format, the entity type and TIN type are consistent (an EIN-vs-SSN mismatch gets flagged), and every required field is filled. It checks for duplicates by TIN and business name so the same contractor can't be onboarded twice. Then finance opens a review queue, reads each submission, sanity-checks the classification, and clicks Approve. Only on approval does the contractor flip to a payable vendor — and you get an approved-vendor CSV in the exact columns your accounting/AP system expects.
What's inside the Implementation Plan
The downloadable plan is a step-by-step file you paste into an AI coding agent. It opens by interviewing you about your business — how you onboard contractors today, which AP/accounting system you pay them from and exactly what its vendor-import columns are named, which entity types and classification questions you actually need, your typical and peak onboarding volume, who has to approve, and the messy edge cases (foreign contractors who need a W-8, single-member LLCs, name/TIN mismatches) — and then it tailors the data model, the validations, and every later step to your answers. This is not a generic template; the agent reflects a short spec back to you and waits for your thumbs-up before it builds anything. From there it walks the agent through the secure intake link, the W-9 form and classification questions, the TIN and entity validation, the duplicate guard, the finance review-and-approve queue, and the approved-vendor CSV export — each step with a ready-to-copy prompt. There's also a fallback so you can build and use the whole thing today even with no API to your accounting system.
The governance it includes (this is the point)
This is sensitive tax tooling — TINs are exactly the kind of data you do not want leaking — so it ships with the controls a finance team needs: login so only your team can use the internal side, row-level security so you only ever see your own organization's contractors, a complete audit trail of who reviewed and approved which onboarding and when, and a hard human-approval gate so no contractor becomes payable until finance signs off. Duplicate guards keyed on TIN and business name stop the same contractor from being onboarded twice. And because TIN/EIN/SSN are sensitive, the plan encrypts them at rest, masks them in the UI (you see only the last four digits), and locks every record behind RLS.
Who it's for
AP and finance teams, controllers, and ops people who pay independent contractors and are tired of collecting tax data after the fact. If you can describe how your shop decides a contractor is cleared to pay, you can build this.
You've got this — start with the plan, paste the first prompt, answer the interview, and you'll see your first clean onboarding move through the queue the same afternoon.