Mettle

Mettle is a digital-only business bank account brand for UK sole traders, freelancers, and small limited companies, wholly owned by NatWest Group and originally built with Capco. It has no physical branches and is run on separate technology from the core NatWest bank, offering an app-based current account with a UK sort code and account number, invoicing, bookkeeping, tax tools, and a free FreeAgent accounting integration. As a NatWest Group brand, Mettle participates in UK Open Banking through NatWest Group's "Bank of APIs" developer platform, publishing PSD2 / OBIE-conformant APIs - a public, unsecured Open Data (Product) API describing its business current accounts, plus the FAPI-secured Read/Write family (Account & Transaction Information, Payment Initiation, and Confirmation of Funds). Read/Write access runs against a live production gateway (api.openbanking.prd-mettle.co.uk) secured with OAuth2/OIDC, mutual-TLS client authentication, and PSD2 strong customer authentication using OBIE/eIDAS certificates, onboarded via the Bank of APIs portal. Mettle is delivered under NatWest Group's FCA-authorised banking group and is a challenger/digital proposition rather than one of the CMA9 mandated brands.

Mettle publishes 1 API on the APIs.io network: Open Data Product API. Tagged areas include Financial Services, Banking, Business Banking, Open Banking, and PSD2.

Mettle’s developer surface includes authentication, sandbox, documentation, engineering blog, support, and 22 more developer resources.

🌐 Visit website 📡 Source on GitHub
46.7/100 developing ▬ flat Agent 78/100 agent native Full breakdown ↓
scored 2026-07-27 · rubric v0.5
AccessSelf serve
4 APIs 1 MCP Servers
Financial ServicesBankingBusiness BankingOpen BankingPSD2OBIEFAPIUnited KingdomPaymentsAccount InformationChallenger BankFintech

Kin Score

Kin Score Kin Score How this is scored →
scored 2026-07-27 · rubric v0.5
Composite quality — 46.7/100 · developing
Contract Quality 9.4 / 25
Developer Ergonomics 11.3 / 20
Commercial Clarity 5.8 / 20
Operational Transparency 3.1 / 13
Governance 0.0 / 12
Discoverability 10.0 / 10
Agent readiness — 78/100 · agent native
Machine-Readable Contract 18 / 18
Agentic Access Contract 15 / 15
MCP Server 12 / 12
Machine-Readable Auth 10 / 10
Idempotency 9 / 9
Stable Error Semantics 8 / 8
Request/Response Examples 0 / 7
Rate-Limit Signaling 0 / 7
Typed Event Surface 0 / 6
Agent Skills 5 / 5
Well-Known Catalog 4 / 4
Consent & Bot Identity 0 / 3
Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. This rating is computed from github.com/api-evangelist/mettle: open an issue to ask a question, or submit a pull request to add artifacts. Want it done for you? Prioritized profiling — $2,500 →

APIs 4

Individual APIs this provider publishes, each with its own machine-readable definition.

Mettle Open Data Product API

Mettle's public, unsecured UK Open Banking Open Data (Product) API, exposing reference information about the business current accounts Mettle offers to sole traders and limited ...

Mettle Account and Transaction API

OBIE Read/Write Account & Transaction Information (AIS) API for Mettle business current accounts, exposing accounts, balances, transactions, and related resources to FCA-authori...

Mettle Payment Initiation API

OBIE Read/Write Payment Initiation Services (PIS) API for Mettle, allowing FCA-authorised third parties to initiate domestic and other payments from a customer's Mettle account ...

Mettle Confirmation of Funds API

OBIE Read/Write Confirmation of Funds (CBPII) API for Mettle, letting card-based payment instrument issuers confirm whether funds are available on a customer's Mettle account. F...

MCP Servers 1

Model Context Protocol servers that expose these APIs to AI agents.

mettle-mcp.yml

MCP SERVER

Security Posture 2

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Mettle Authentication

oauth2/openIdConnect/mutualTLS · 3 schemes

SECURITY

Mettle Domain Security

TLSv1.3 · HSTS · DMARC

SECURITY

Scopes 1

OAuth scopes governing access to this provider's APIs.

Mettle Scopes

4 scopes · authorizationCode/clientCredentials

4 scopes

SCOPES

Agentic Access 1

Recommended x-agentic-access execution contracts for AI agents.

Mettle Agentic Access

12 operations

12 operations · 0 acting

AGENTIC

Resources

Get Started 2

Portal, sign-up, and the first successful call

Sandbox
Sandbox
 DeveloperPortal
DeveloperPortal

Documentation 1

Reference material describing how the API behaves

Documentation
Documentation

Agent Surfaces 5

MCP servers, agent skills, and machine-readable catalogs

AgenticAccess
AgenticAccess
 WellKnown
WellKnown
 MCPServer
MCPServer
 LLMsTxt
LLMsTxt
 AgentSkill
AgentSkill

Design & Contract 6

Pagination, idempotency, versioning, errors, and events

Conformance
Conformance
 Conventions
Conventions
 Idempotency
Idempotency
 ErrorCatalog
ErrorCatalog
 Lifecycle
Lifecycle
 DataModel
DataModel

Access & Security 4

Authentication, authorization, and security posture

DomainSecurity
DomainSecurity
 Authentication
Authentication
 OAuthScopes
OAuthScopes
 Compliance
Compliance

Operate 3

Status, limits, changes, and where to get help

Deprecation
Deprecation
 StatusPage
StatusPage
 Support
Support

Commercial 2

Pricing, plans, and the legal terms of use

TermsOfService
TermsOfService
 PrivacyPolicy
PrivacyPolicy

Company 3

The organization behind the API

Website
Website
 Blog
Blog
 LinkedIn
LinkedIn

Other 1

Properties that don't map to a standard resource type

Overlay
Overlay

Source (apis.yml)

apis.yml Raw ↑ 
aid: mettle
url: https://raw.githubusercontent.com/api-evangelist/mettle/refs/heads/main/apis.yml
name: Mettle
kind: company
description: Mettle is a digital-only business bank account brand for UK sole traders, freelancers, and small limited companies,
  wholly owned by NatWest Group and originally built with Capco. It has no physical branches and is run on separate technology
  from the core NatWest bank, offering an app-based current account with a UK sort code and account number, invoicing, bookkeeping,
  tax tools, and a free FreeAgent accounting integration. As a NatWest Group brand, Mettle participates in UK Open Banking
  through NatWest Group's "Bank of APIs" developer platform, publishing PSD2 / OBIE-conformant APIs - a public, unsecured
  Open Data (Product) API describing its business current accounts, plus the FAPI-secured Read/Write family (Account & Transaction
  Information, Payment Initiation, and Confirmation of Funds). Read/Write access runs against a live production gateway (api.openbanking.prd-mettle.co.uk)
  secured with OAuth2/OIDC, mutual-TLS client authentication, and PSD2 strong customer authentication using OBIE/eIDAS certificates,
  onboarded via the Bank of APIs portal. Mettle is delivered under NatWest Group's FCA-authorised banking group and is a challenger/digital
  proposition rather than one of the CMA9 mandated brands.
accessModel:
  pricing: unknown
  onboarding: self-serve
  trial: false
  try_now: false
  public: false
  label: Self-serve signup
  confidence: medium
  source:
  - authentication
  generated: '2026-07-23'
  method: derived
image: https://kinlane-images.s3.amazonaws.com/shared/apis-json/apis-json-logo.jpg
tags:
- Financial Services
- Banking
- Business Banking
- Open Banking
- PSD2
- OBIE
- FAPI
- United Kingdom
- Payments
- Account Information
- Challenger Bank
- Fintech
created: '2026-07-23'
modified: '2026-07-23'
specificationVersion: '0.21'
apis:
- aid: mettle:mettle-open-data-product-api
  name: Mettle Open Data Product API
  description: Mettle's public, unsecured UK Open Banking Open Data (Product) API, exposing reference information about the
    business current accounts Mettle offers to sole traders and limited companies. Conforms to the OBIE Open Data API standard;
    no credentials required to read.
  humanURL: https://www.bankofapis.com/products/natwest-group-open-banking/products-and-locations/documentation/mettle
  baseURL: https://api.openbanking.prd-mettle.co.uk/open-banking/v2.3
  tags:
  - Open Data
  - Business Current Accounts
  - Products
  properties:
  - type: OpenAPI
    url: openapi/mettle-open-data-api-openapi.json
  - type: Documentation
    url: https://www.bankofapis.com/products/natwest-group-open-banking/products-and-locations/documentation/mettle
  - type: APIReference
    url: https://www.bankofapis.com/products/natwest-group-open-banking/products-and-locations/documentation/mettle
- aid: mettle:mettle-account-transaction-api
  name: Mettle Account and Transaction API
  description: OBIE Read/Write Account & Transaction Information (AIS) API for Mettle business current accounts, exposing
    accounts, balances, transactions, and related resources to FCA-authorised third parties. FAPI-secured with OAuth2/OIDC,
    mTLS, and PSD2 strong customer authentication.
  humanURL: https://www.bankofapis.com/products/accounts/documentation/mettle
  baseURL: https://api.openbanking.prd-mettle.co.uk/open-banking/v3.1/aisp
  tags:
  - Account Information
  - Transactions
  - AIS
  properties:
  - type: Documentation
    url: https://www.bankofapis.com/products/accounts/documentation/mettle
  - type: APIReference
    url: https://www.bankofapis.com/products/accounts/documentation/mettle
- aid: mettle:mettle-payment-initiation-api
  name: Mettle Payment Initiation API
  description: OBIE Read/Write Payment Initiation Services (PIS) API for Mettle, allowing FCA-authorised third parties to
    initiate domestic and other payments from a customer's Mettle account with their consent. FAPI-secured with OAuth2/OIDC,
    mTLS, and PSD2 strong customer authentication.
  humanURL: https://www.bankofapis.com/products/payments/documentation/mettle
  baseURL: https://api.openbanking.prd-mettle.co.uk/open-banking/v3.1/pisp
  tags:
  - Payment Initiation
  - Payments
  - PIS
  properties:
  - type: Documentation
    url: https://www.bankofapis.com/products/payments/documentation/mettle
  - type: APIReference
    url: https://www.bankofapis.com/products/payments/documentation/mettle
- aid: mettle:mettle-confirmation-of-funds-api
  name: Mettle Confirmation of Funds API
  description: OBIE Read/Write Confirmation of Funds (CBPII) API for Mettle, letting card-based payment instrument issuers
    confirm whether funds are available on a customer's Mettle account. FAPI-secured with OAuth2/OIDC, mTLS, and PSD2 strong
    customer authentication.
  humanURL: https://www.bankofapis.com/products/card-based-payments/documentation/mettle
  baseURL: https://api.openbanking.prd-mettle.co.uk/open-banking/v3.1/cbpii
  tags:
  - Confirmation of Funds
  - CBPII
  - Funds Check
  properties:
  - type: Documentation
    url: https://www.bankofapis.com/products/card-based-payments/documentation/mettle
  - type: APIReference
    url: https://www.bankofapis.com/products/card-based-payments/documentation/mettle
common:
- type: AgenticAccess
  url: agentic-access/mettle-agentic-access.yml
- type: DomainSecurity
  url: security/mettle-domain-security.yml
- type: Authentication
  url: authentication/mettle-authentication.yml
- type: OAuthScopes
  url: scopes/mettle-scopes.yml
- type: Conformance
  url: conformance/mettle-conformance.yml
- type: Compliance
  url: https://www.bankofapis.com/products/natwest-group-open-banking
- type: Conventions
  url: conventions/mettle-conventions.yml
- type: Idempotency
  url: conventions/mettle-conventions.yml
- type: ErrorCatalog
  url: errors/mettle-problem-types.yml
- type: Lifecycle
  url: lifecycle/mettle-lifecycle.yml
- type: Deprecation
  url: https://www.bankofapis.com/products/natwest-group-open-banking
- type: DataModel
  url: data-model/mettle-data-model.yml
- type: WellKnown
  url: well-known/mettle-well-known.yml
- type: MCPServer
  url: mcp/mettle-mcp.yml
- type: LLMsTxt
  url: llms/mettle-llms.txt
- type: Overlay
  url: overlays/mettle-open-data-api-overlay.yaml
- type: Sandbox
  url: https://developer.sandbox.natwest.com/
- type: AgentSkill
  url: skills/_index.yml
- type: Website
  url: https://www.mettle.co.uk/
- type: DeveloperPortal
  url: https://www.bankofapis.com/
- type: Documentation
  url: https://www.bankofapis.com/products/natwest-group-open-banking/products-and-locations/documentation/mettle
- type: StatusPage
  url: https://www.bankofapis.com/performance/service-interruptions
- type: Blog
  url: https://www.mettle.co.uk/blog/
- type: LinkedIn
  url: https://www.linkedin.com/company/join-mettle
- type: Support
  url: https://www.mettle.co.uk/contact-us/
- type: TermsOfService
  url: https://www.mettle.co.uk/docs/terms-and-conditions/1.5.pdf
- type: PrivacyPolicy
  url: https://www.mettle.co.uk/privacy-notice/
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com