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 20 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 $15,000
Maintenance Reserve $12,500
Other $2,500

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 20 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 95% 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 work full-time in the Stellar ecosystem; the SDKs are my main work.

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, and since Q3 2026 for the KMP SDK

Bence ([ngybnc][ngybnc]) is a Soneso team member and works with me on the SDK. He has worked on the KMP SDK since February 2026 and authored the Native ScVal Conversion deliverable of Q3 2026.

Retroactive Impact

In Q3 2026 the SDK shipped six releases, v1.9.0 through v1.14.0. Maven Central artifacts recorded about 32,000 downloads from roughly 2,100 unique sources over the quarter (Scarf), nearly double the quarter before, which had about 17,000 downloads from 1,100 sources. At the close of the quarter: 15 stars, 5 forks, 29 releases, 0 open issues, and 0 open pull requests. Unit test coverage is tracked on Codecov and enforced in CI with a 90% minimum, currently at 95.12%, up from 81% at the proposal.

SEP-51 (XDR-JSON) shipped in v1.11.0. Apps can now convert any Stellar XDR data, the binary format of transactions and ledger data, to readable JSON and back. The JSON follows the standard form defined by SEP-51, which the Python and PHP SDKs use as well. Developers can inspect and edit transactions and contract data as text, which makes debugging easier and lets them exchange data with other tools.

Native ScVal Conversion shipped in v1.13.0. When an app calls a smart contract, the answer comes back in Stellar’s binary format, which the app had to take apart by hand. The new helper turns such a value into a plain Kotlin value with one call, without the contract’s interface description, so apps can use contract results directly. Bence ([ngybnc][ngybnc]), a Soneso team member on the KMP SDK since February 2026, authored this deliverable.

Contract Bindings (KMP Target) added Kotlin as a new target of the community code generator, next to the Dart, Swift, and PHP targets that Soneso contributed, and the Stellar CLI now points developers to it for Kotlin as well. Developers can generate ready-to-use Kotlin code for talking to any smart contract with one command, and the generated code runs on the current SDK, including contracts that use external-reference executables (Protocol 28).

The SDK supported the quarter’s network upgrades ahead of time. Protocol 27, the upgrade the proposal named, was tracked through its mainnet activation on 2026-07-08, and the SDK now uses the new authorization format it introduced (CAP-71) by default. Support for Protocol 28 followed in v1.12.0 on 2026-08-26, 21 days before the network switched on 2026-09-16. That gave app developers time to prepare for contracts that share code through external references (CAP-85), which the SDK can load and deploy.

Maintenance made the SDK safer for users. Addresses and incoming binary data are checked more strictly on every platform, so a mistyped address or a malformed data packet is caught early. Sign-in with anchors (SEP-10) and anchor callbacks (SEP-12) are verified more strictly as well.

Smart accounts became easier to build into wallets. A wallet can now install policies, such as a spending limit, at the moment it creates an account, an addition the proposal did not name. Input that the smart-account contract would reject, such as an overlong rule name or too many policies on one rule, is caught before the transaction is sent, so the wallet learns about it without paying a fee. And every error the OpenZeppelin smart-account contracts can return is translated into a named error the wallet can explain to its user. In web apps, a lost network connection now arrives as a specific error the app can handle.

Documentation kept pace: the [SEP guides][sepguides] index now covers all 20 implemented SEPs, a new guide explains Stellar address types, and a migration guide walks developers through the upgrade to v1.12.0. The compatibility matrices show full coverage of Horizon and Soroban RPC through v28.0.1, and every SEP matrix is at 100%. CI stays current through Dependabot, security updates of the build tooling, and a check that flags upstream XDR changes. SBOM submission to PG Atlas runs on every push to the default branch. The SDK joined the [soneso-sdk-stats][statsdash] dashboard this quarter, which tracks maintenance and usage of all four Soneso SDKs.

Past Deliverables

2026 Q3

1. Continuous Maintenance and Improvement (2026 Q3)

Description from last quarter:

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 of completion:

  • Release notes: [v1.9.0][rel190], [v1.10.0][rel1100], [v1.11.0][rel1110], [v1.12.0][rel1120], [v1.13.0][rel1130], [v1.14.0][rel1140]
  • Protocol 27 tracked through its mainnet activation: CAP-71 useUpgradedAuth simulation flag and RPC v27.1 fields (v1.9.0), ADDRESS_V2 credentials as the default (v1.12.0): [PR #45][pr45], commit 41d0466cc, [PR #62][pr62]
  • Support for Protocol 28 ahead of its mainnet activation: CAP-85 external-reference executables in XDR (v1.11.0), external-reference resolution, deployment from an external reference, and contract id derivation (v1.12.0): [PR #50][pr50], [PR #59][pr59], [PR #60][pr60], [PR #61][pr61], [protocol delivery ledger][protoledger]
  • Horizon and XDR updates: claimable balance ids in every spelling and nullable balance-change accounts (v1.12.0), one client identification on every request path (v1.14.0), XDR definitions at the current upstream stellar-xdr (v1.13.0): [PR #58][pr58], [PR #74][pr74], [PR #70][pr70]
  • Soroban and network handling: transaction polling reports the last failure and network errors in web apps arrive as typed exceptions (v1.10.0), Horizon event streams reconnect reliably, RPC decoding errors carry a clear message, and contract deployment reports a refused transaction immediately (v1.11.0): [PR #47][pr47], [PR #54][pr54], commit d1a7d2310
  • Stricter input validation: strkeys on all platforms, hex parsing, and amount strings (v1.12.0), XDR array counts checked before allocation and WebAuthn length checks (v1.14.0): [PR #58][pr58], commit 713bb5144, [PR #73][pr73], [PR #74][pr74]
  • Unit test coverage raised from 81% to 95.12%, past the 85% the proposal targeted, with a restructured test suite and a 90% minimum enforced in CI and as a required check (v1.11.0): [PR #54][pr54], Codecov, codecov.yml
  • SEP-6, SEP-10, and SEP-29 updates: transaction patching per the spec, challenge source account verified and token requests never auto-retried, memo-required check fires on submission (v1.11.0): [PR #54][pr54], commit d1a7d2310
  • SEP-8, SEP-12, SEP-23, and SEP-45 updates: strict strkey decoding on all platforms, callbacks and issuers verified more strictly (v1.12.0), authorization entries checked for array counts (v1.14.0): [PR #58][pr58], [PR #73][pr73]
  • Smart-account hardening: contract limits, indexer defaults, and error catalog (v1.10.0), relayer response parsing and signer input checks (v1.11.0), ADDRESS_V2 defaults with a relayer opt-out and demo apps updated for Protocol 28 (v1.12.0): [PR #47][pr47], [PR #54][pr54], [PR #62][pr62], commit 1f15e94b9
  • Documentation: accuracy pass with every code sample compiled (v1.12.0), migration guide for v1.12.0, guide to Stellar address types (v1.13.0), agent skill updated every release: commit f8fbdc67e, [1.12.0 guide][mig1120], [PR #71][pr71], agent skill
  • Compatibility matrices regenerated every release, Horizon and RPC at 100% through v28.0.1 and every SEP matrix at 100% (v1.14.0): [Horizon][q3horizon], [RPC][q3rpc], [SEP][q3sep]
  • CI and SBOM: Dependabot updates with pinned actions, XDR generator on a patched xdrgen fork with the fix proposed upstream (v1.10.0), API reference published from the main branch (v1.14.0), SBOM submitted to PG Atlas on every push to the default branch: [PR #64][pr64], commit ef89d7d2f, commit 53b7fa495, [stellar/xdrgen PR #231][xdrgen231], [PR #72][pr72], [SBOM runs][sbomruns]
  • KMP SDK added to the soneso-sdk-stats dashboard, with Maven Central download collection and the SDK’s maintenance profile: [dashboard commit d842da410][statscd842da4], [dashboard][statsdash], [KMP profile][profile]

Six releases shipped this quarter. Protocol 27 was tracked through its mainnet activation, and support for Protocol 28 followed in v1.12.0 on 2026-08-26, 21 days before the network switched on 2026-09-16. Compatibility matrices were regenerated for every release: Horizon and RPC report 100% through v28.0.1, and every SEP matrix reports 100%.

2. SEP-51 (XDR-JSON)

Description from last quarter:

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.

Delivered in v1.11.0 (2026-08-10).

Proof of completion:

  • GitHub release: [v1.11.0][rel1110]
  • PR with implementation and round-trip tests (v1.11.0): [PR #57][pr57]
  • SEP-51 compatibility matrix, 37 of 37 fields: [SEP-51 matrix][sep51matrix]
  • Documentation: [SEP-51 guide][sep51doc]
  • Weekly check of the round-trip corpus against the reference implementation: [corpus drift workflow][corpusdriftworkflow]

Every generated XDR type converts to and from the SEP-51 JSON form with toXdrJson() and fromXdrJson(). Round-trip tests run in CI against a corpus from the reference implementation, and a test executes every example in the guide.

3. Native ScVal Conversion

Description from last quarter:

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.

Delivered in v1.13.0 (2026-09-15).

Proof of completion:

  • GitHub release: [v1.13.0][rel1130]
  • PR with implementation and tests (v1.13.0): [PR #67][pr67]
  • Documentation: [PR #68][pr68], [guide section][guidesection]

SCValXdr.toNative() turns contract values into plain Kotlin values with one call, without the contract’s interface description, and never throws. Values without a Kotlin counterpart come back unchanged. The helper is documented in the usage guide and the agent skill reference.

4. Contract Bindings (KMP Target)

Description from last quarter:

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.

Delivered in v1.9.0 (2026-07-14) for the SDK addition, stellar-contract-bindings 0.6.0b0 (2026-09-02) for the generator target, and stellar-cli v28.1.0 (2026-09-26) for the CLI subcommand.

Proof of completion:

  • Pull request to stellar-contract-bindings, new Kotlin Multiplatform target: [PR #22][scb22], [KMP commit][scb22kmp]
  • Follow-up, spec-text escaping for multi-line contract docs: [PR #36][scb36]
  • Follow-up, CAP-85 external-reference resolution in the generator: [PR #37][scb37]
  • Generator release: [0.6.0b][scbrel]
  • Pull request to stellar-cli, the stellar contract bindings kmp subcommand that points developers to the generator, released in v28.1.0: PR #2721, v28.1.0
  • SDK release with the client addition, a raw-value invoke path on ContractClient (v1.9.0): [v1.9.0][rel190], [PR #44][pr44]
  • Generated Kotlin clients tested in unit and testnet integration tests, regenerated with the released generator (v1.13.0): [generated clients][generatedclients], [PR #65][pr65]
  • Documentation of generated bindings (v1.13.0): [PR #66][pr66]

Six generated clients run as testnet integration tests in the SDK repository. Generated Kotlin code calls contracts through the SDK’s ContractClient and covers contracts that share code through external references.

Beyond the committed scope (2026 Q3)

The following work was not named in the Q3 proposal.

  • Constructor-time smart-account policies (v1.10.0): [PR #47][pr47]

Proposed Impact

Keep the SDK compatible with Horizon, Soroban RPC, and protocol updates, starting with the Horizon and RPC 29.0.0 releases. Maintain existing SEP implementations and update as needed. Fix bugs and respond to issues and feature requests.

Make the SDK more reliable for the apps that use it. In addition to the regular maintenance, this quarter will run a hardening round: an AI-assisted review of the whole SDK has proposed a list of security hardening measures, bug fixes, and improvements to code, tests, and documentation. The round will validate each proposal and work through the valid ones as far as the quarter allows.

Make Stellar assets easier to use in apps that work with smart contracts. Add a Stellar Asset Contract toolkit, so an app can open XLM or any issued asset as a Soroban contract with the same client it uses for other contracts, look up the asset’s contract id, read a balance, and build a transfer. The JS SDK already provides this.

Proposed Deliverables

Continuous Maintenance and Improvement

Regular SDK updates addressing Horizon, Soroban RPC, and protocol updates (the Horizon and RPC 29.0.0 releases, then every following protocol release, each supported before its mainnet activation), bug fixes, feature requests, and documentation updates. Maintain existing SEP implementations and update as needed. Keep compatibility matrices, the AI agent skill, CI pipelines, statistics dashboard, and SBOM workflow up to date.

Hardening round: an AI-assisted review of the whole SDK has proposed a list of security hardening measures, bug fixes, and improvements to code, tests, and documentation. We will check and validate each proposal; valid proposals will become issues in the repository, labeled as part of this round, and will be worked through as far as the quarter allows, security hardening and bug fixes first, then the improvements.

Dated duties: the SDK’s dependency data will keep reaching PG Atlas through GitHub’s API change on 2026-11-13. Before GitHub moves its default runners to Ubuntu 26.04 (rollout 2026-10-19 to 2026-11-19), we will verify the Linux CI jobs (unit tests and coverage, documentation pages, SBOM submission, SEP-51 conformance check, XDR update check) on Ubuntu 26.04 and adapt them where they break.

Commitments for the quarter, each checkable from public data:

  1. First maintainer response to every community issue and pull request within 48 hours. Proof: responsiveness panel of the [soneso-sdk-stats dashboard][statsdash].
  2. Every protocol release supported before its mainnet activation, with the Horizon and RPC matrices regenerated at each Horizon and RPC release. Proof: [protocol delivery ledger][protoledger], matrix headers.
  3. Unit test coverage at or above 90% under the required Codecov check; Horizon, RPC, and every SEP matrix at 100% at each release. Proof: Codecov report, matrices in the repository.
  4. No release with an open dependency advisory, with Dependabot covering every dependency manifest. Proof: release notes, Dependabot configuration.
  5. The dated duties done by their dates. Proof: workflow runs.

Proof: Release notes on GitHub, the labeled issues of the hardening round and their PRs, updated compatibility matrices, workflow runs, the Codecov report, and the soneso-sdk-stats dashboard.

Stellar Asset Contract Toolkit

Add Stellar Asset Contract (SAC) support to the high-level contract client: a client for an asset’s contract opened from the SAC interface description shipped with the SDK, the contract id derived from the asset, a balance read, a transfer builder, and read calls that need no funded account, with unit tests, a testnet integration test, a documentation section, and the agent skill reference.

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

Metrics loaded from PG Atlas

PG Atlas 90d Contributors Pony Factor Adoption

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

[corpusdriftworkflow]: https://github.com/Soneso/kmp-stellar-sdk/blob/v1.14.0/.github/workflows/sep-51-corpus-drift.yml [generatedclients]: https://github.com/Soneso/kmp-stellar-sdk/tree/v1.14.0/stellar-sdk/src/commonTest/kotlin/com/soneso/stellar/sdk/contract/bindings [guidesection]: https://github.com/Soneso/kmp-stellar-sdk/blob/v1.13.0/docs/sdk-usage-examples.md#spec-less-conversion-with-tonative [mig1120]: https://github.com/Soneso/kmp-stellar-sdk/blob/v1.12.0/docs/migration/1.12.0.md [ngybnc]: https://github.com/ngybnc [pr44]: https://github.com/Soneso/kmp-stellar-sdk/pull/44 [pr45]: https://github.com/Soneso/kmp-stellar-sdk/pull/45 [pr47]: https://github.com/Soneso/kmp-stellar-sdk/pull/47 [pr50]: https://github.com/Soneso/kmp-stellar-sdk/pull/50 [pr54]: https://github.com/Soneso/kmp-stellar-sdk/pull/54 [pr57]: https://github.com/Soneso/kmp-stellar-sdk/pull/57 [pr58]: https://github.com/Soneso/kmp-stellar-sdk/pull/58 [pr59]: https://github.com/Soneso/kmp-stellar-sdk/pull/59 [pr60]: https://github.com/Soneso/kmp-stellar-sdk/pull/60 [pr61]: https://github.com/Soneso/kmp-stellar-sdk/pull/61 [pr62]: https://github.com/Soneso/kmp-stellar-sdk/pull/62 [pr64]: https://github.com/Soneso/kmp-stellar-sdk/pull/64 [pr65]: https://github.com/Soneso/kmp-stellar-sdk/pull/65 [pr66]: https://github.com/Soneso/kmp-stellar-sdk/pull/66 [pr67]: https://github.com/Soneso/kmp-stellar-sdk/pull/67 [pr68]: https://github.com/Soneso/kmp-stellar-sdk/pull/68 [pr70]: https://github.com/Soneso/kmp-stellar-sdk/pull/70 [pr71]: https://github.com/Soneso/kmp-stellar-sdk/pull/71 [pr72]: https://github.com/Soneso/kmp-stellar-sdk/pull/72 [pr73]: https://github.com/Soneso/kmp-stellar-sdk/pull/73 [pr74]: https://github.com/Soneso/kmp-stellar-sdk/pull/74 [profile]: https://soneso.github.io/soneso-sdk-stats/profiles/kmp-stellar-sdk.json [protoledger]: https://github.com/Soneso/soneso-sdk-stats/blob/main/curated/protocol-delivery.json [q3horizon]: https://github.com/Soneso/kmp-stellar-sdk/blob/v1.14.0/compatibility/horizon/HORIZON_COMPATIBILITY_MATRIX.md [q3rpc]: https://github.com/Soneso/kmp-stellar-sdk/blob/v1.14.0/compatibility/rpc/RPC_COMPATIBILITY_MATRIX.md [q3sep]: https://github.com/Soneso/kmp-stellar-sdk/tree/v1.14.0/compatibility/sep [rel1100]: https://github.com/Soneso/kmp-stellar-sdk/releases/tag/v1.10.0 [rel1110]: https://github.com/Soneso/kmp-stellar-sdk/releases/tag/v1.11.0 [rel1120]: https://github.com/Soneso/kmp-stellar-sdk/releases/tag/v1.12.0 [rel1130]: https://github.com/Soneso/kmp-stellar-sdk/releases/tag/v1.13.0 [rel1140]: https://github.com/Soneso/kmp-stellar-sdk/releases/tag/v1.14.0 [rel190]: https://github.com/Soneso/kmp-stellar-sdk/releases/tag/v1.9.0 [sbomruns]: https://github.com/Soneso/kmp-stellar-sdk/actions/workflows/sbom.yml [scb22]: https://github.com/lightsail-network/stellar-contract-bindings/pull/22 [scb22kmp]: https://github.com/lightsail-network/stellar-contract-bindings/commit/49885f1ad [scb36]: https://github.com/lightsail-network/stellar-contract-bindings/pull/36 [scb37]: https://github.com/lightsail-network/stellar-contract-bindings/pull/37 [scbrel]: https://github.com/lightsail-network/stellar-contract-bindings/releases/tag/0.6.0b [sep51doc]: https://github.com/Soneso/kmp-stellar-sdk/blob/v1.11.0/docs/sep/sep-51.md [sep51matrix]: https://github.com/Soneso/kmp-stellar-sdk/blob/v1.14.0/compatibility/sep/SEP-0051_COMPATIBILITY_MATRIX.md [sepguides]: https://github.com/Soneso/kmp-stellar-sdk/blob/main/docs/sep/README.md [statscd842da4]: https://github.com/Soneso/soneso-sdk-stats/commit/d842da410 [statsdash]: https://soneso.github.io/soneso-sdk-stats/ [xdrgen231]: https://github.com/stellar/xdrgen/pull/231

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