kmp-stellar-sdk

Write your Stellar integration once in Kotlin and run it across Mobile, Web, Desktop, and Server: transactions, Stellar RPC and Horizon, smart contracts, OpenZeppelin smart accounts, and 17 SEPs.

   
Category SDKs
Website https://developers.stellar.org/docs/tools/sdks/client-sdks#kotlin-multiplatform-sdk
Repository https://github.com/Soneso/kmp-stellar-sdk
First Released October 2025
Intake https://github.com/SCF-Public-Goods-Maintenance/scf-public-goods-maintenance.github.io/issues/86
Budget Requested 15000

Project Description

The Kotlin Multiplatform Stellar SDK lets developers write their Stellar integration once in Kotlin and run it across Mobile (Android and iOS), Web (browser), Desktop (JVM, native macOS), and Server (JVM, Node.js). It covers XDR encoding and decoding, transaction building and signing, Stellar RPC and Horizon, low-level and high-level Soroban smart-contract support (deploy, simulate, invoke, auth-entry signing), OpenZeppelin smart account support (WebAuthn passkeys, multi-signer authorization, context rules, and policy-based access control), and 17 Stellar Ecosystem Proposals (SEPs). It ships two cross-platform demo apps (general-purpose and smart-account) and an AI coding-agent skill. It is open-source (Apache-2.0), published on Maven Central, listed on the official Stellar developer documentation, built on audited cryptography (BouncyCastle, libsodium), and tested on CI with 81% unit test coverage tracked on Codecov, with zero open issues.

Team & Experience

My name is Christian, also known as Soneso in the Stellar community, and I am the main developer and maintainer of several Stellar Client SDKs.

I began contributing to the Stellar network in 2017, specializing primarily in the development and maintenance of Stellar SDKs. I developed the iOS Stellar SDK, the Flutter Stellar SDK, the PHP Stellar SDK, and the Kotlin Multiplatform Stellar SDK. I currently work full-time on my Stellar SDK projects.

Previous SCF participation:

  • Multiple SCF Build Awards, including the KMP Stellar SDK OZ smart account support and wallet SDKs for Dart and Swift
  • SCF Public Goods Award since Q3 2025 (Batch 1) for the iOS, Flutter, and PHP SDKs

Retroactive Impact

In Q2 2026 the KMP Stellar SDK shipped multiple releases — v1.3.1 through v1.8.1. At the close of the quarter: 0 open issues, a 100% issue response rate, with a median time-to-close of 16.6 hours. The Maven Central artifacts recorded about 17,000 downloads from roughly 1,100 unique sources over the last three months (Scarf). Unit test coverage is tracked on Codecov, currently at 81%.

The headline delivery is OpenZeppelin smart account support, shipped in v1.4.0: WebAuthn passkey authentication on all platforms, multi-signer authorization, context rules and policies, relayer-sponsored fees, and indexer-based credential discovery, together with a Compose Multiplatform smart account demo app (Android, iOS, macOS, web). The feature grew across the quarter: cross-device passkey authentication via WebAuthn hybrid transport (v1.5.0), a hardened wallet-connect cascade (v1.5.1), Ed25519 external signers (v1.6.1), and token-decimals support with stricter amount validation (v1.7.1). The smart-account feature was funded by an SCF Build Award (RFP Track); all other work this quarter, and the SDK’s ongoing maintenance, was self-funded.

SEP-31 (Cross-Border Payments, sending side, requested by a community member on Discord) landed in v1.6.0 together with a shared callback-signature verifier for SEP-12 and SEP-31, bringing the SDK to 17 implemented SEPs. Protocol 27 (CAP-71) Soroban authorization shipped in v1.8.0, with the compatibility matrices regenerated against Horizon and Soroban RPC v27.0.0.

Release v1.8.1 added a headless connectToContract path with RPC-visibility polling and an agent-signer flow in the smart account demo: a standalone Kotlin reference agent, a Ktor coordination server, and an approval inbox — the flow where a user delegates scoped authority to an agent, over-scope calls are rejected on-chain and surfaced for approval, and the approved call is re-submitted via the relayer.

The XDR code generator gained upstream source pinning, snapshot tests, and daily upstream-drift monitoring, and a generator bug collapsing multi-case discriminants was fixed. CI runs on every push with Codecov coverage tracking and monthly Dependabot updates, the AI-agent skill is updated alongside each release, and SBOM submission to PG Atlas runs on every push to main.

Past Deliverables

This is the SDK’s first Public Goods Award proposal; it enters the program through the accepted New Project Intake (issue 86, linked above), so there are no committed deliverables from a previous award quarter to report. What the SDK shipped last quarter, before any Public Goods funding, is covered under Retroactive Impact.

Proposed Impact

Keep the SDK compatible with Horizon, Soroban RPC, and protocol updates including Protocol 27. Maintain existing SEP implementations and update as needed. Fix bugs and respond to issues and feature requests.

Implement SEP-51 (XDR-JSON), a standard mapping between Stellar’s XDR structures and JSON. This enables developers to inspect and manipulate XDR data in a human-readable format, improving debugging and tooling integration. The Python SDK and the PHP SDK already implement this SEP.

Improve the Soroban developer experience by adding a helper that converts a returned smart-contract value (SCValXdr) to a native Kotlin value without requiring the contract spec, so contract invocation and simulation results can be consumed directly instead of parsing the raw XDR union by hand. The JS and Python SDKs already provide this.

Add a Kotlin Multiplatform target to the community stellar-contract-bindings generator (implemented by overcat and linked from the Stellar CLI), so developers can generate typed Kotlin contract clients from a deployed contract’s spec, joining the Dart, Swift, and PHP targets that Soneso contributed (see: stellar-contract-bindings generator).

Proposed Deliverables

Continuous Maintenance and Improvement

Regular SDK updates addressing Horizon, Soroban RPC, and protocol updates (tracking Protocol 27 through its mainnet activation), bug fixes, feature requests, and documentation updates. Maintain existing SEP implementations and update as needed, keep the compatibility matrices current. Improve unit test coverage toward 85% (currently 81%). Keep CI pipelines and the SBOM workflow up to date, and add the KMP SDK to the soneso-sdk-stats dashboard so its statistics are tracked alongside the other Soneso SDKs (see: soneso-sdk-stats dashboard).

Proof: Release notes on GitHub, updated compatibility matrices, Codecov coverage report, and the soneso-sdk-stats dashboard.

SEP-51 (XDR-JSON)

Implement bi-directional XDR/JSON conversion via the XDR generator, with round-trip unit tests and documentation, for cross-SDK parity with the Python and PHP SDKs.

Proof: GitHub release, PR with implementation and tests, SEP-51 compatibility matrix, documentation.

Native ScVal Conversion

Add a helper that converts a smart-contract value (SCValXdr) to a native Kotlin value without requiring the contract spec, so contract invocation and simulation results can be consumed directly instead of parsing the raw XDR union by hand. This matches the JS and Python SDKs.

Proof: GitHub release, PR with implementation and tests, documentation.

Contract Bindings (KMP Target)

Add a Kotlin Multiplatform target to the community stellar-contract-bindings generator (implemented by overcat and linked from the Stellar CLI), generating typed Kotlin contract clients backed by the SDK’s ContractClient and joining the Dart, Swift, and PHP targets that Soneso contributed. Includes the SDK addition the generated clients need (a public raw-SCVal invoke path on ContractClient). Once the generator target is merged, add a stellar contract bindings kmp subcommand to the Stellar CLI, as with the existing subcommands for the other languages.

Proof: pull requests to the stellar-contract-bindings and stellar-cli repositories, SDK release with the client addition, generated-code tests.

Metrics loaded from PG Atlas

PG Atlas 90d Contributors Pony Factor Adoption

  • As the project representative, I agree to the Legal Acknowledgements.

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