You check your bank balance in a budgeting app. Your employer deposits your salary without printing a single slip of paper. A small business owner in Chicago receives a payment from a buyer in Singapore within seconds. None of this happens by magic. Behind every one of these moments is a piece of technology that most people have never heard of: a banking API.
Banking APIs are quietly running the modern financial world. And in 2025, the global open banking market built on them was worth over $31 billion, growing at nearly 28% per year.1 Yet for most people, including many professionals inside the industry, the term remains fuzzy. In this article, we dive into exactly what banking APIs are, how they work, why they matter, and what the numbers tell us about where banking is heading.
First, What Even Is an API?
API stands for Application Programming Interface. It sounds very technical, but the idea is actually quite simple: an API is a set of rules that lets two software systems talk to each other.
| Think of It This Way When you go to a restaurant, you do not walk into the kitchen and cook your own food. You tell a waiter what you want, and the waiter communicates your order to the kitchen. The kitchen prepares your meal and sends it back via the waiter. An API is the waiter. It takes a request from one system (you), delivers it to another system (the kitchen), and brings back the result. |
In banking, APIs allow external applications, whether that is a mobile app, an accounting tool, or a corporate payment system, to securely communicate with a bank’s core systems. They can request account information, initiate payments, verify identities, and much more, all without the user needing to log into the bank’s own website or app.
Why Do Banking APIs Matter?
To understand why APIs matter, it helps to understand what banking looked like before them.
The Traditional Way vs. The New Way
| The Traditional Way (Pre-API) | The New Way (API-Powered) |
| Companies exchanged data through manual file uploads | Data flows automatically, in real time |
| Checking balances across multiple banks required logging into each one individually | One app can pull balances from all banks at once |
| International wire transfers took 3 to 5 business days | Cross-border payments can settle the same day |
| Adding a new banking partner took weeks of technical setup | API connections can be built in days |
| Payment errors were discovered after the fact | Pre-validation APIs catch errors before sending |
The shift from manual processes to API-driven automation is a fundamental change in what is possible, and for organizations that have made the switch, the results are measurable.
The Scale of Banking APIs Today
Open banking APIs are not a niche experiment. They are already a central infrastructure for the global financial system.
| $31.6B Global open banking market value in 20241 | 137B API calls made in open banking in 20252 | 27.6% Annual market growth rate through 20301 |
| 16.5M Active UK open banking user connections (Dec 2025)3 | 351M Open banking payments in the UK in 20253 | 32 Countries with open banking frameworks in place or in active development4 |
In the United Kingdom, the country with the most mature open banking ecosystem, weighted API availability (a measure of uptime across all participating banks, adjusted for each bank’s share of total transaction volume) held above 99.5% throughout 2025, with average response times of just 324 milliseconds. This is faster than a blink of the human eye!3
How a Banking API Actually Works
When a piece of software makes a banking API call, here is what happens step by step:
- Request Comes In: The application sends a request to the bank’s API endpoint, a specific URL address assigned to a particular function (such as “get balance” or “send payment”).
- Authentication: The bank’s system checks the request to verify if the caller is who they say they are.
- Authorization: The system then checks what this caller is allowed to do.
- Request Processed: If both checks pass, the bank processes the request, such as looking up the account balance or initiating a transfer.
- Response Sent: The bank sends back a structured response, usually in a format called JSON, which is essentially a list of labelled values (e.g. “balance”: 4250.00, “currency”: “USD”).
- Request Settlement: The application receives the response and uses it, perhaps displaying the balance on screen, or recording the transaction.
| The whole exchange typically takes less than one second. For a corporate treasury team processing thousands of payments a day, this speed and automation translate directly into efficiency, accuracy, and cost savings. |
One important design principle: banking APIs are stateless. Each request contains everything needed to process it, including all credentials and instructions. The bank server does not need to remember anything from previous requests. This makes API systems extremely scalable, because servers can handle millions of independent requests simultaneously.
The Five Main Types of Banking APIs
Not all banking APIs do the same thing. There are five main categories, each serving a distinct purpose.
| API Type | What It Does | Real-World Example |
| Account Information (AIS) | Reads account data: balances, transactions, standing orders. Read-only, no money movement. | A budgeting app that shows all your bank accounts in one dashboard |
| Payment Initiation (PIS) | Instructs a bank to send a payment directly from an account, without a card. | Paying for a purchase online via a direct bank transfer instead of entering a card number |
| Bank-to-Bank / SWIFT APIs | Connects financial institutions to each other and to global payment networks. Enables real-time tracking of cross-border payments. | A bank tracking exactly where an international wire is at every stage of its journey |
| eBAM / Treasury APIs | Manages bank account structures and cash positions programmatically. Automates account opening, cash sweeps, and reporting. | A multinational company automatically consolidating cash from 50 accounts into a single pool each day |
| Compliance & Reference Data APIs | Provides verified data for sanctions screening, identity checks, and payment routing validation. | A bank automatically checking a payment recipient against global watchlists before executing the transfer |
| Key Fact: In the UK open banking system, roughly 4 out of every 5 API calls are Account Information requests. Payment Initiation calls grew 53% in 2025 alone.3 |
Open Banking: The Regulation That Made APIs Mainstream
Banking APIs did not become widespread by accident. Governments and regulators pushed banks to open up their systems through formal rules. This movement is called Open Banking.
The core idea: your financial data belongs to you, not your bank. You should be able to share it with whomever you choose, securely and easily.
| Region | Framework | Key Facts |
| European Union | PSD2 (2019) | Requires banks to allow licensed third parties to access account data and initiate payments via APIs. |
| United Kingdom | Open Banking (2017) | The most mature API ecosystem globally. 95% of banks participate. 16.5M active user connections as of December 2025.3 |
| United States | Section 1033 / FDX (2024) | The CFPB’s final rule gives consumers the right to share their financial data via standardized APIs, moving the US toward a formal open banking framework. |
| Brazil | Open Finance (2021) | Over 102 billion API calls processed in 2024 and 61.9 million active consents by end of 2024. One of the fastest-growing programs globally.5 |
| Australia | Consumer Data Right | Extends open banking principles to energy and telecoms, not just financial services. |
| India | Account Aggregator | A rapidly growing open finance ecosystem serving a population-scale financial infrastructure, with over 120 million accounts linked as of 2024.6 |
Is It Safe? How Banking APIs Are Secured
Security is the question most people ask first, and rightly so. Banking APIs handle sensitive financial data and real money. The industry has developed layered security specifically for this purpose.
| Security Layer | What It Does in Plain English |
| TLS Encryption (minimum v1.2) | Every message sent between systems is scrambled, so it cannot be intercepted and read in transit. This is the same protection used on all HTTPS websites. |
| OAuth 2.0 Access Tokens | Instead of sharing a password, the bank issues a short-lived “token” (like a temporary visitor pass) that gives exactly the right level of access for a limited time. |
| Strong Customer Authentication (SCA) | Before any access is granted or payment sent, the user must verify their identity using at least two methods: something they know (a PIN), something they have (a phone), or something they are (a fingerprint). |
| Mutual TLS (mTLS) | Both the bank and the connecting application must present verified digital certificates to each other. Neither side can impersonate the other. |
| Consent Management | Users explicitly grant and can revoke data access at any time. Every consent is logged. An app cannot access more than what was specifically approved. |
| Rate Limiting & Monitoring | API gateways limit how many requests can be made in a given period and flag unusual activity automatically, blocking potential abuse before it causes harm. |
| Important: Under proper implementation of open banking, third-party apps never see your bank password or card number. Your credentials stay with your bank. Access is granted via tokens, which can expire and be cancelled at any moment. |
What Banking APIs Make Possible: Key Benefits
For Businesses and Corporations
- Real-time cash visibility across all banking relationships, not just prior-day statements
- Automated payment processing that eliminates manual file uploads and human review
- Cross-border payments that settle the same day, with full tracking at every stage
- Pre-validation of payment details before sending, catching errors before they cause problems
- Seamless integration between accounting systems, ERPs, and banking platforms
- eBAM automation that replaces paper-based bank account management
For Consumers
- Personal finance apps that show all bank accounts in one place
- Faster loan and mortgage approvals because lenders can verify income in real time
- Cheaper online payments via direct bank transfers instead of card processing fees
- More competition in financial services, meaning better products and lower costs
For the Financial System as a Whole
- Richer payment data through ISO 20022, improving fraud detection and compliance screening
- Reduced cost and complexity for correspondent banking and cross-border settlement
- A foundation for embedded finance, where banking capabilities are built into non-bank platforms
| What Is Embedded Finance? Embedded finance means banking features (payments, lending, insurance) built directly into non-financial apps. When you buy something on an e-commerce platform and pay via direct bank transfer at checkout, that is embedded finance powered by a Payment Initiation API. It is one of the fastest-growing areas of fintech, because it meets people where they already are, inside the apps they use every day, without needing to visit a bank. |
ISO 20022: The Data Language Behind Modern Payments
When banking APIs exchange payment information, they need a shared language. That language is ISO 20022.
ISO 20022 is an international standard that defines exactly what information a payment message must contain and how it should be structured. Think of it as the difference between a sticky note that says “pay Bob” and a properly completed payment form with Bob’s full name, as well as relevant addresses, account numbers, references, and purpose codes.
| Old Format (MT Messages) | ISO 20022 (New, MX Standard) |
| Limited field sizes, data often truncated | Unlimited structured fields, full data preserved |
| Counterparty details frequently incomplete | Full debtor and creditor information mandatory |
| No standard remittance reference field | Rich remittance data included in every message |
| Different banks interpret fields differently | Consistent, globally agreed-upon structure |
| Harder to screen for compliance automatically | Structured data makes automated screening far more accurate |
SWIFT completed its migration of cross-border payment messaging to ISO 20022 in 2025. Almost 200 market infrastructure initiatives globally have adopted the standard. For any organization that sends or receives international payments, ISO 20022 compliance is now the baseline expectation, not an optional upgrade.7
How Axletree Solutions Brings It All Together
Understanding banking APIs in theory is one thing. Implementing them across a real organization, with multiple banking relationships, legacy systems, compliance requirements, and format incompatibilities, is an entirely different challenge. This is where Axletree has spent 25 years building expertise.
Founded as the first Swift Service Bureau in North America, Axletree today processes over $150 billion in financial messaging every day, across more than 1.2 million transactions. Our solutions are used by banks, corporates, insurers, healthcare providers, logistics companies, and technology firms around the world.8
| Solution | What It Does | How It Connects to APIs |
| AxleConnect™ | A single connectivity gateway supporting SWIFT, RTP, and Host-to-Host rails | Connects organizations to any payment network via a single managed API gateway, eliminating the need to build and maintain separate connections for each bank or network |
| Symmetree by Axletree® | An enterprise data transformation engine for financial formats | Converts between ISO 20022, SWIFT MT, CSV, and proprietary bank formats automatically, so any system can speak to any other without custom coding for each pair |
| Swift Service Bureau | Fully managed end-to-end SWIFT connectivity | Delivers full-suite Swift connectivity, without clients needing to run their own SWIFT infrastructure |
| Swift Professional Services | Support from Swift-certified experts on a range of Swift needs | Support for ongoing Swift initiatives, mandates, assessments, and more, including recent API-first initiatives |
| RADAR by Axletree™ | Compliance audit and assessment platform | Automates evidence collection and monitoring for SWIFT Customer Security Programme compliance, especially important for API-connected environments that must balance speed with security |
| AxleLink™ | Single-window portal for payment lifecycle visibility | Aggregates data from all payment channels, including API-connected channels, into one operational dashboard, giving treasury and operations teams a real-time view of every transaction |
Specific Services That Leverage Banking APIs
- Swift GPI Services: Real-time cross-border payment tracking with same-day settlement guarantees
- Swift Payment Pre-Validation: Checks payment details against live reference data before submission, preventing costly rejections
- Swift Case Management: Resolves payment discrepancies through a structured, API-integrated workflow
- SwiftRef Integration: Provides real-time access to global reference data (BIC codes, IBAN structures, routing information) to validate payments at the point of entry
- ISO 20022 Advisory and Implementation: Guides institutions through the migration from legacy MT formats to the new ISO 20022 standard
- Axletree’s Integration Services: Connects ERP, TMS, and core banking systems using Symmetree’s any-to-any format transformation engine
| The Axletree Advantage 99.99% service continuity, so payments keep moving24/7/365 live expert support, not automated ticketingBespoke solution design around each client’s specific systems and needsFast implementation with ongoing maintenance fully handled by Axletree25 years of proven expertise as a Swift-certified, globally trusted partner |
The Bottom Line
Banking APIs are the current infrastructure of modern finance. Every time money moves faster than a paper form allows, every time a business has real-time visibility into its cash, every time a payment arrives before the recipient expected it, a banking API made it possible.
The organizations that have moved quickly to build API-based connectivity are already operating with lower costs, faster settlement, better compliance, and more flexible relationships with their banking partners. Those still relying on batch processes and manual file transfers are leaving efficiency, and competitive advantage, on the table.
The good news is that building this connectivity does not require an organization to become a technology company. It just requires the right partner.
| Ready to Build Your Banking API Strategy? Axletree has been engineering enterprise financial connectivity for 25 years. Whether you need to implement SWIFT connectivity, migrate to ISO 20022, automate treasury operations, or design a compliant open banking integration, our certified experts are ready to help. Visit axletrees.com or contact us at info@axletrees.com to speak directly with a financial connectivity expert. |
References:
1 Grand View Research, “Open Banking Market Size & Share | Industry Report, 2030,” grandviewresearch.com. Market value estimated at USD 31.61 billion in 2024; CAGR of 27.6% from 2025 to 2030.
2 Juniper Research, “Open Banking API Call Volume to Surpass 720 Billion Globally by 2029,” press release, 24 February 2025. juniperresearch.com. Total open banking API calls projected at 137 billion in 2025.
3 Open Banking Limited, “Open Banking in 2025: Now Part of the UK’s Everyday Financial Life,” openbanking.org.uk, January 2026. Source for: 16.5M active user connections (Dec 2025); 351M UK payments in 2025; weighted API availability above 99.5%; average response time of 324ms; 4 in 5 API calls being AIS; 53% PIS growth in 2025.
4 Twimbit / F5, “2025 Global State of Open Finance Report.” The report’s Global Open Finance Maturity Index evaluates readiness across 32 countries. Also cited in: bai.org, “How open finance could redefine global banking in 2025 and beyond,” August 2025.
5 Ozone API, “The Status of Open Finance in Latin America in 2025,” ozoneapi.com, August 2025. Citing Banco Central do Brasil data: 61.9 million active consents in 2024; 102 billion total API calls processed in 2024 (annual figure).
6 Government of India, Department of Financial Services, Account Aggregator Framework progress update (as of 31 December 2025), financialservices.gov.in: over 2.61 billion financial accounts enabled for data sharing; 120 million accounts linked as of December 2024 (CGAP). 7 SWIFT, ISO 20022 Programme. SWIFT completed migration of CBPR+ cross-border payment messages to ISO 20022 in November 2025. SWIFT states that “almost 200” market infrastructure initiatives globally have adopted the standard. See swift.com/standards/iso-20022.
8 Axletree Solutions, company profile and service documentation. axletree.com. Figures of $150 billion in daily financial messaging and 1.2 million daily transactions are as stated by Axletree.
