Reaching account-level data inside Yellowstone Bank’s YB app

Nine branches across south-central Montana, around $661M in assets per branch-locator data, and a 2022 mobile relaunch on App Store ID 1636547513 — that is the surface area an integration with Yellowstone Bank actually touches. The working path on behalf of a member is an authorized session running against the YB app and the portal at go.yellowstone.bank, with what comes back mapped into something a host system can use.

The bottom line for an integrator: Yellowstone Bank is a small charter on a modern digital-banking front end. The data is rich (transactions carry user-added tags, notes and receipt photos), but the access path is the member, not a network connector. We build to that path.

What sits behind the YB login

Mapped against the in-app menus and the bank’s Online & Mobile Banking description, here is what an integration would actually move:

What the YB app does not really hold — investment positions, brokerage flows, treasury rails — is out of frame because Yellowstone Bank itself does not run those products in the app. The integration is scoped to what is actually behind that login.

Routes we’d run for this bank

Three routes are realistic for a charter this size; one is the spine, the others fill specific gaps.

1. Authorized session against the member’s account

The member signs an authorization, hands us the credentials they already use for internet banking, and our integration runs the same login the YB app would — CSRF bootstrap, password POST, MFA when prompted, then the dashboard endpoints behind go.yellowstone.bank. This is durable, covers every domain in the table above, and is the route that actually runs for a bank this size. Access is arranged with the customer during onboarding, including the consent paperwork.

2. Aggregator network where the bank is already linked

For host apps that already speak to a Plaid, MX or Finicity network connector and only need YB as one of many institutions, we wire to that connector and add YB-specific normalization. Coverage and reliability of a network connector for a $661M-asset community bank are uneven, so we treat this as a complement to route 1, not a substitute.

3. Native PDF e-statement ingest

The YB app exposes electronic statements as PDFs. For archival backfills — the “give me the last 24 months even if no transaction API will hand them over” ask — the cleanest path is to pull the statement PDFs and parse them. Slow, but reliable, and the member can run it themselves under the same consent.

For most YB builds, route 1 does the day-to-day work, route 3 fills in archival history the session cannot reach, and route 2 is worth wiring only when a connector network is already in your host stack.

Session sketch — what the login actually looks like

Illustrative only; the exact endpoint paths, body fields and challenge order are confirmed during the build against a consenting member’s account.

# Authorized session against Yellowstone Bank's member portal,
# scoped by the consenting member's written authorization.
import httpx

s = httpx.Client(
    base_url="https://go.yellowstone.bank",
    headers={"User-Agent": "OBS-YB-Integration/1.0"},
    timeout=20.0,
)

# 1) Bootstrap the login screen for CSRF + device fingerprint nonce.
boot = s.get("/")
csrf = parse_csrf(boot.text)

# 2) Post the member's internet-banking credentials.
s.post("/auth/login", data={
    "username": cfg["user"],
    "password": cfg["pass"],
    "_csrf":   csrf,
})

# 3) Handle the OTP / device-cookie challenge if the bank asks for it.
if needs_mfa(s):
    handle_otp(s, cfg["otp_callback"])

# 4) Walk the account list, then pull current balance + last 90 days.
accounts = s.get("/api/dashboard/accounts").json()
for acct in accounts:
    txns = s.get(
        f"/api/accounts/{acct['id']}/transactions",
        params={"from": "2026-02-23", "to": "2026-05-24"},
    ).json()
    upsert(acct, txns)        # normalize into the host warehouse

# 5) Statement archive: walk the statement index, save PDFs.
for stmt in s.get("/api/statements").json():
    save_pdf(stmt["id"], s.get(stmt["pdf_url"]).content)

What is real in that sketch: the credential reuse between the app and the portal, the MFA step at login, the per-account walk, and the statement PDFs. What is illustrative: the exact path shapes. We replace the placeholders with what the live session actually returns during the build.

What ships when the build is done

Each engagement ends with a working artifact, not a slide deck. For a Yellowstone Bank build, that is typically:

• An OpenAPI / Swagger spec for the endpoints we mapped — accounts, transactions, statements, transfers, alerts, debit-card state — with request and response shapes annotated.
• A short protocol & auth-flow report covering the YB login chain: CSRF + password POST, the MFA challenge path, and the session-cookie behaviour we observed.
• Runnable source for the key endpoints in Python (httpx, as the sketch above) and Node.js. Both run against a consenting member’s account end-to-end.
• Automated tests pinned to the response fields the host system actually consumes — so when the YB front end changes, the test screams before production does.
• A normalization layer that maps YB’s transaction shape into a stable schema (id, posted_at, amount, type, counterparty, tags, notes, receipt_image_ref) so the rest of the host system doesn’t care which bank produced the row.
• An interface documentation doc with the actual request / response captures from the build, plus a section on consent storage and revocation for the bank’s compliance file.

Consent, member authorization, and where US data-rights rules sit

A Yellowstone Bank integration runs on two pieces of paper that already exist for this kind of work: the member’s written authorization to share their banking data with a named third party, and the existing terms of service the member accepted when they opened the YB account. Both predate any federal open-banking regime; both are what FDIC-supervised community banks have relied on to permit member-driven third-party access for years. We log the consent, scope it to the data domains the host actually needs, and honour revocation by tearing down the session and purging cached data.

The CFPB’s Section 1033 Personal Financial Data Rights rule is on the horizon but not, as of this writing, in force: per the CFPB’s own reconsideration notice and the court order in Forcht Bank v. CFPB, enforcement of the rule is enjoined while the Bureau reconsiders it, and the agency has been seeking comments to inform that rewrite. For a $661M-asset Montana charter, that means the eventual smaller-charter compliance window is open-ended; we track it but do not anchor today’s build to it, and the dependable basis stays the member’s authorization. We will revisit the wiring if and when the rule lands in a form that changes what a bank of this size has to expose.

Engineering notes from the YB mapping

A few things we account for on this specific build, so the integration behaves on day 30 and not just day 1:

• Front-end refresh after the 2022 relaunch. The YB app was rebuilt in 2022, per its “new app” description and the 2022 App Store id. Vendor-driven UI refreshes on this platform shift endpoint paths and field names without warning, so the build includes a small synthetic-account probe that runs on a cadence and shouts the moment a response shape moves; that is what keeps the integration alive past the next refresh.
• MFA is a real branch, not a happy-path footnote. The bank’s online-banking help and the mobile flow both invoke device-fingerprint plus OTP challenges. We model the OTP step as a callback the host provides — SMS forwarding, email pickup, or an in-host UI prompt — so the integration doesn’t silently stall the first time a new device hits the login.
• User-attached transaction metadata. The YB app lets the member add tags, free-text notes and receipt or check photos to a transaction. Most aggregator-style integrations drop these because they do not exist on a generic schema; we map them onto a per-row metadata bag so the host can keep what the member actually put there.
• Statement backfill belongs on its own track. The statement endpoint behaves like a static archive, not a real-time feed. We schedule it monthly rather than wedging it into the same loop as balances and transactions, and we let it run slow without blocking the rest of the sync.

Engagement and pricing

Pricing starts at $300 for source-code delivery, paid only after you have looked at what arrived and signed off. That model gives you the runnable Python and Node source, the OpenAPI spec, the protocol report and the tests — everything to run the Yellowstone Bank integration on your own infrastructure. The alternative is our hosted endpoints on a pay-per-call basis: no upfront fee, you call our API, we bill the calls. A typical Yellowstone Bank build is a one-to-two-week cycle, and access plus the consent paperwork are arranged with you during that window.

If either model sounds like the right shape, the next step is a short note about what you want from the YB data and which accounts the consenting members hold — reach the studio at /contact.html and we will scope the rest.

Interface evidence

Screens pulled from the Play Store listing for com.yellowstonebank.grip. Click to enlarge.

Other Montana mobile-banking apps in scope

Adjacent charters and credit unions you might bundle into the same integration program. Plain references, not endorsements; the data behind each is what the institution itself exposes to its own members.

• Stockman Bank of Montana — a larger Montana-headquartered bank publishing several mobile apps (personal, eBiz, MyMortgage); broadly the same account-and-transaction surface as YB plus business cash management.
• First Interstate Bank — multi-state community bank with deep Montana presence; mobile app covers retail accounts, deposits and card controls.
• First Bank of Montana — Lewistown-based community bank; mobile banking app includes mobile pay (Apple Pay / Google Pay / Samsung Pay) on top of standard account access.
• Glacier Bank — Kalispell-headquartered Glacier Bancorp subsidiary; member apps share a common digital stack across the bank’s Montana branches.
• First Security Bank Montana — Bozeman-area community bank with mobile deposit and account access in its app.
• Manhattan Bank — small Montana charter publishing a personal mobile banking app focused on deposit accounts.
• American Bank Montana — Bozeman-headquartered; mobile app covers personal and business deposit accounts.
• Opportunity Bank of Montana — statewide Montana bank with a retail mobile banking app and bill pay.
• TrailWest Bank — western Montana community bank with mobile banking, card controls and deposit capture.
• Pioneer Federal Savings and Loan — Montana savings institution publishing a member mobile app for deposit and loan accounts.

Questions integrators tend to raise about YB specifically

Where this brief comes from

Drawn from the bank’s own Online & Mobile Banking pages and digital-upgrade announcements, the Play Store listing for com.yellowstonebank.grip, public branch-locator data, and current CFPB filings on Section 1033 reconsideration. The asset and branch numbers are as published by BankBranchLocator and are not independently audited here. Sources opened during the mapping:

• Yellowstone Bank — Online & Mobile Banking
• Yellowstone Bank — “It’s here: an upgraded digital banking experience”
• Google Play — Yellowstone Bank app listing
• CFPB — Personal Financial Data Rights Reconsideration
• BankBranchLocator — The Yellowstone Bank

Mapping desk: OpenBanking Studio integration engineering — written 24 May 2026.