Mcp Abap Adt Compact

[mcp-abap-adt logo] mcp-abap-adt: Your Gateway to ABAP Development Tools (ADT)

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mcp-abap-adt is an MCP server for ABAP ADT in SAP ECC/S/4HANA (on-premise) and SAP BTP ABAP Cloud systems. It gives agents controlled access to real ABAP repositories through ADT, so analysis and changes are grounded in system data instead of assumptions. It is built for AI-assisted pair programming (AIPNV: AI Pairing, Not Vibing), not autopilot vibe coding.

Primary workflows:

• Deep ABAP analysis: where-used, object metadata, repository navigation, object structure, semantic analysis, dependency and impact exploration.
• High-level ABAP development: rapid CRUD and iterative updates for RAP and classic ABAP artifacts (classes, interfaces, function groups/modules, programs, DDIC, CDS/view/service artifacts), validated through ADT flows.

Why teams use it:

• Full CRUD (not read-only): create, read, update, and delete ABAP artifacts
• Works with On-Premise (ECC/S/4HANA) and ABAP Cloud (BTP) systems
• Legacy systems (BASIS < 7.50) are not supported at present: that support is parked on the parked/legacy-support branch until it can be tried against a live legacy system
• Four authentications: basic (HTTP or RFC), SNC (passwordless, RFC), JWT with browser login (service key, ABAP or XSUAA) and JWT you already hold
• Multiple transports: stdio, HTTP, SSE
• Several installation variants: the full server (@mcp-abap-adt/core) or the compact one (@mcp-abap-adt/compact), each connecting to the system over HTTP, RFC or SNC — see Installation variants
• Rich tool surface for ABAP objects, metadata, transports, and search

Authorization & Destinations (Important): A destination is the filename of a service key stored locally. You place service keys in the service-keys directory, and use --mcp=<destination> to select which one to use. This is the primary auth model for on‑prem and BTP systems. See Authentication & Destinations.

You can configure MCP clients either manually (JSON/TOML) or via the configurator CLI (@mcp-abap-adt/configurator, repo: mcp-abap-adt-conf).

Table of Contents

1. Getting Started
2. Architecture
3. Quick Start
4. Use Cases
5. Target Users
6. Capabilities (High-Level Focus)
7. Terminology
8. Authorization & Destinations
9. Registries
10. Features
11. Documentation
12. Dependencies
13. Running the Server

Getting Started

Pick a variant first — full or compact server, and HTTP, RFC or SNC to the system. HTTP needs nothing but Node.js 22 or 24; RFC and SNC need the SAP NW RFC SDK and a C++ toolchain on the machine before npm install, because the RFC module is compiled during the install and silently left out when it cannot be. Installation variants has the table and the commands; RFC Setup the steps.

Install the server and configure your client using the configurator:

npm install -g @mcp-abap-adt/corenpm install -g @mcp-abap-adt/configurator
# stdio (destination)mcp-conf --client cline --name abap --mcp TRIAL
# HTTP (streamable HTTP)mcp-conf --client copilot --name abap --transport http --url http://localhost:3000/mcp/stream/http --mcp trial

Full configurator usage (separate repo): CLIENT_INSTALLERS.md.

Terminology

Destination: a local service key filename. You store service keys in the standard service-keys directory, and pass the filename (without extension) via --mcp=<destination> to select which system to use.

See docs/user-guide/TERMINOLOGY.md for the full list.

Authorization & Destinations

Destination-based auth is the default. Drop service keys into the standard platform folder and use the filename as your destination:

mcp-abap-adt --transport=stdio --mcp=TRIAL

Standard service key paths:

• Unix (Linux/macOS): ~/.config/mcp-abap-adt/service-keys/<destination>.json
• Windows: %USERPROFILE%\\Documents\\mcp-abap-adt\\service-keys\\<destination>.json

The server supports exactly four authentications; each is a destination stated in a service key, a .env, or both:

A jwt .env must state SAP_GRANT_TYPE. The mcp-auth command that writes such a .env comes from @mcp-abap-adt/auth-broker-cli. The browser login listens on port 61001 unless --browser-auth-port says otherwise.

A created object always carries its responsible person: the first stated of the tool's own argument, the x-sap-responsible header, SAP_RESPONSIBLE in the destination's own .env, then in the process environment — else the login: on-premise the destination's SAP_USERNAME, the x-sap-login of an x-sap-url connection, the process SAP_USERNAME; on a cloud system only the system's user. A create that finds none (SNC, a token you hold) is refused naming SAP_RESPONSIBLE; nothing is sent — a message class included, from 17.0.0. The master system comes from x-sap-master-system or SAP_MASTER_SYSTEM (destination .env, then process) — no tool takes it as an argument — else from a cloud system itself; otherwise it is left out and the system applies itself — never refused. Reads are unaffected. The process environment is read once: a change made to it while the server runs is not picked up. See Authentication & Destinations. Coming from 16.x? See the 17.0 migration note — the HTTPS certificate is now verified. From 15.x, the 16.0 note first.

For full details (paths, .env, direct headers), see Authentication & Destinations.

Architecture

The project ships as two packages — and a compact variant of each — because the two usage patterns want different licences. Embedding the tools in a network service should not drag in the obligations of a server that service never runs.

Install @mcp-abap-adt/core (or @mcp-abap-adt/compact) to run a server. Install @mcp-abap-adt/lib to embed the tools in your own application.

1. Standalone MCP Server (Default)

Run as a standalone MCP server with stdio, HTTP, or SSE transport:

mcp-abap-adt                           # stdio (default)mcp-abap-adt --transport=http          # HTTP modemcp-abap-adt --transport=sse           # SSE mode

2. Embeddable Server (For Integration)

Embed MCP server into existing applications (e.g., SAP CAP/CDS, Express). This needs @mcp-abap-adt/lib only — not the AGPL server:

npm install @mcp-abap-adt/lib

import {  EmbeddableMcpServer,  NoDedupStrategy, // optional: expose both Read<X> and Get<X>} from '@mcp-abap-adt/lib/embeddable';
const server = new EmbeddableMcpServer({  connection,              // Your AbapConnection instance  logger,                  // Optional logger  exposition: ['readonly', 'high'],  // Handler groups to expose  // Default hides Read<X> when Get<X> is exposed (ReadVsGetDedupStrategy).  // Pass NoDedupStrategy to expose both variants instead.  // readOnlyDedupStrategy: new NoDedupStrategy(),});await server.connect(transport);

See Handlers Management → EmbeddableMcpServer dedup strategies for how readonly tools are deduped against high/low, how to opt out with NoDedupStrategy, and how to plug a custom IReadOnlyDedupStrategy for role-based rules.

Quick Start

1. Install server: pick the installation variant — full or compact, HTTP, RFC or SNC — and follow the Installation Guide
2. Configure client (auto): Use mcp-conf from @mcp-abap-adt/configurator (repo: mcp-abap-adt-conf, docs: CLIENT_INSTALLERS.md)
3. Configure client (manual): See Client Configuration
4. Use:
   • Read-Only Tools
   • High-Level Tools
   • Low-Level Tools

Use Cases

• Impact analysis / where-used before changes: map object usage and probable blast radius.
• Dependency audit: inspect links across classes, interfaces, DDIC, CDS/views, and RAP artifacts.
• Migration and cleanup prep: extract repository facts to plan refactoring or cloud-readiness work.
• RAP and ABAP iterative development: create/update artifacts quickly with ADT-backed operations.
• Automated documentation and RAG ingestion: pull structured facts from ABAP systems for downstream tooling.

Target Users

• ABAP developers and ABAP architects
• RAP developers
• Team leads and tech leads who need fast repository visibility
• Teams building RAG/agent workflows for SAP landscapes

Capabilities (High-Level Focus)

Key examples of high-value workflows and tools:

• Repository and impact analysis: GetWhereUsed, DescribeByList, GetObjectStructure, GetObjectInfo, SearchObject, GetPackageTree, GetPackageContents
• Code and semantic introspection: GetAbapAST, GetAbapSemanticAnalysis, GetIncludesList
• RAP development: CreateBehaviorDefinition, UpdateBehaviorDefinition, CreateBehaviorImplementation, UpdateBehaviorImplementation, CreateServiceDefinition, UpdateServiceDefinition, CreateMetadataExtension, UpdateMetadataExtension
• CDS/View development: CreateView, UpdateView, GetView, DeleteView
• ABAP OO CRUD: CreateClass, UpdateClass, GetClass, DeleteClass, CreateInterface, UpdateInterface, GetInterface, DeleteInterface
• Function module/group CRUD: CreateFunctionGroup, UpdateFunctionGroup, GetFunctionGroup, DeleteFunctionGroup, CreateFunctionModule, UpdateFunctionModule, GetFunctionModule, DeleteFunctionModule
• Transport and activation support: CreateTransport, GetTransport, ActivateObject
• Quality and testing: RunATC, GetATCRunStatus, GetATCFindings (ABAP Test Cockpit — one run over several objects, findings read back by worklist), ABAP Unit per test carrier — CreateUnitTest/UpdateUnitTest/DeleteUnitTest/RunUnitTest for a class, CreateCdsUnitTest/RunCdsUnitTest for a CDS view, CreateProgramUnitTest/RunProgramUnitTest for a report, CreateFunctionGroupUnitTest/RunFunctionGroupUnitTest/RunFunctionModuleUnitTest for a function group (a run waits for its result; GetUnitTestResult for one that outlasts the wait) — CheckClass and the rest of the Check* family

Registries

Published in the official MCP Registry and listed on Glama.ai.

• MCP Registry: docs/deployment/MCP_REGISTRY.md
• Glama.ai: [图片]

Features

• 🏗️ Domain Management: GetDomain, CreateDomain, UpdateDomain - Create, retrieve, and update ABAP domains
• 📊 Data Element Management: GetDataElement, CreateDataElement, UpdateDataElement - Create, retrieve, and update ABAP data elements
• 📦 Table Management: GetTable, CreateTable, GetTableContents - Create and retrieve ABAP database tables with data preview
• 🏛️ Structure Management: GetStructure, CreateStructure - Create and retrieve ABAP structures
• 👁️ View Management: GetView, CreateView, UpdateView - Create and manage CDS Views and Classic Views
• 🎓 Class Management: GetClass, CreateClass, UpdateClass - Create, retrieve, and update ABAP classes
• 📝 Program Management: GetProgram, CreateProgram, UpdateProgram - Create, retrieve, and update ABAP programs
• 🔧 Behavior Definition (BDEF) Management: GetBehaviorDefinition, CreateBehaviorDefinition, UpdateBehaviorDefinition - Create and manage ABAP Behavior Definitions with support for Managed, Unmanaged, Abstract, and Projection types
• 📋 Metadata Extension (DDLX) Management: CreateMetadataExtension, UpdateMetadataExtension - Create and manage ABAP Metadata Extensions
• ⚡ Activation: ActivateObject - Universal activation for any ABAP object
• 🚚 Transport Management: CreateTransport, GetTransport - Create and retrieve transport requests
• 🔍 Enhancement Analysis: GetEnhancements, GetEnhancementImpl, GetEnhancementSpot - Enhancement discovery and analysis
• 📋 Include Management: GetIncludesList - Recursive include discovery
• 🔍 System Tools: GetInactiveObjects - Monitor inactive objects waiting for activation
• 🌐 Service Binding Preview: GetServiceBindingPreviewUrl - The browser URL that opens a published service binding's Fiori preview, beside its OData service and $metadata URLs. Composed from the binding, its service definition and the exposed root view — no document carries it. OData V2 and V4; a Web API binding has no preview and says so. On SAP BTP the preview URL carries the browser host (abap-web), where the BTP logon answers, while the service URLs keep the ADT host
• 🧪 Runtime Diagnostics: RuntimeCreateProfilerTraceParameters, RuntimeListProfilerTraceFiles, RuntimeGetProfilerTraceData, RuntimeGetDumpById - Profiling and dump analysis with JSON payloads
• 📡 Runtime Feeds: RuntimeListFeeds, RuntimeListSystemMessages, RuntimeGetGatewayErrorLog - Feed reader (dumps — filtered by user, runtime error, exception, object, package or component, and read past SAP's 100 entries per request — system messages, gateway errors), SM02 system messages, Gateway error log
• 🚀 SAP BTP Support: JWT/XSUAA authentication with browser-based token helper
• 🔑 Destination-Based Authentication: Service key-based authentication with automatic token management (see Client Configuration)
• 💾 Freestyle SQL: GetSqlQuery - Execute custom SQL queries via ADT Data Preview API

ℹ️ ABAP Cloud limitation: Direct ADT data preview of database tables is blocked by SAP BTP backend policies. The server returns a descriptive error when attempting such operations. On-premise systems continue to support data preview.

Documentation

For Users

• Docs Index - Full documentation index
• Installation Guide - Installation variants (full or compact; HTTP, RFC or SNC) and platform guides
• RFC Setup - RFC and SNC: the SAP NW RFC SDK and a C++ toolchain before the install
• User Guide - End-user docs (auth, config, tools)
• Authentication & Destinations - Destination-based auth and service keys
• Handlers Management - Enable/disable handler groups
• Configurator: @mcp-abap-adt/configurator (repo: mcp-abap-adt-conf) provides the mcp-conf CLI to auto-configure clients
• Tools by level
  • Read-Only Tools
  • High-Level Tools
  • Low-Level Tools

For Administrators

• Deployment Docs - MCP Registry, Docker, release notes
• Server Configuration - YAML config reference

For Developers

• Architecture Documentation - System architecture and design decisions
• Development Documentation - Testing guides and development resources
• CHANGELOG.md - Version history and changes
• docs/MIGRATION-17.0.md - The HTTPS certificate is verified; a message class needs a responsible
• docs/MIGRATION-16.0.md - Authentication on auth-broker 4: four authentications, destinations
• docs/MIGRATION-14.0.md - The compact facade moved to its own packages and --exposition=compact became the mcp-abap-adt-compact command
• docs/MIGRATION-13.0.md - What a consumer on the 12.x contract changes
• docs/MIGRATION-12.0.md - What a consumer on the 11.x contract changes

Dependencies

Two packages do the work:

• @mcp-abap-adt/connection – connection/auth/session layer
• @mcp-abap-adt/adt-clients – Builder-first ADT clients

and six packages declare the contracts both of them and this project are written against — @mcp-abap-adt/interfaces-adt, -adt-connection (where IAbapConnection and IAdtWireResponse live), -network, -auth, -auth-sap and -utils. They replace the single @mcp-abap-adt/interfaces umbrella, which is no longer published: a consumer naming a contract package directly gets one copy of it in the tree and takes its majors one domain at a time.

The verdict on an ADT answer is a strategy, not a default: since adt-clients 23 no member judges its own answer, and @mcp-abap-adt/adt-strategies holds the readings this project passes to every call. That is what keeps a refusal ADT embeds in an HTTP 200 — an activation that did not activate, a delete that was refused — from reaching a caller as success.

Everything above is installed by npm install and published to npm. @mcp-abap-adt/sap-rfc-lite is optional and only needed for the RFC transport (and so for SNC). It is compiled during npm install against the SAP NW RFC SDK that SAPNWRFC_HOME names, and npm leaves it out without an error when it cannot be — check with npm ls -g @mcp-abap-adt/sap-rfc-lite. See RFC Setup.

Running the Server

Global Installation (Recommended)

After installing globally with npm install -g, you can run from any directory:

# Show helpmcp-abap-adt --help
# Default stdio mode (for MCP clients; requires .env file or --mcp parameter)mcp-abap-adt
# stdio mode (explicit; default when --transport is omitted)mcp-abap-adt --transport=stdio
# HTTP mode on custom port (HTTP requires --transport=http)mcp-abap-adt --transport=http --port=8080
# Use stdio mode with auth-broker (--mcp parameter)mcp-abap-adt --transport=stdio --mcp=TRIAL
# Use env destination from platform sessions storemcp-abap-adt --env=trial
# Use explicit .env file pathmcp-abap-adt --env-path=/path/to/my.env
# SSE mode (requires .env file or --mcp parameter)mcp-abap-adt --transport=sse --port=3001
# SSE mode with auth-broker (--mcp parameter)mcp-abap-adt --transport=sse --mcp=TRIAL
# The compact server takes the same options (npm install -g @mcp-abap-adt/compact)mcp-abap-adt-compact --env-path=/path/to/my.env

Development Mode

npm installnpm run buildnpm test

The checkout is not runnable as a server by itself: server/ takes @mcp-abap-adt/lib as a package. To run a build, pack both and install the tarballs together — see From source.

Environment Configuration

Env resolution:

1. --env-path=<path|file> (or MCP_ENV_PATH) for explicit .env file.
   • Absolute path: used as-is.
   • Relative path or file name only (e.g. my.env): resolved from current working directory.
2. --env=<destination> for destination file in standard sessions store:
   • Unix: ~/.config/mcp-abap-adt/sessions/<destination>.env
   • Windows: %USERPROFILE%\\Documents\\mcp-abap-adt\\sessions\\<destination>.env

Nothing is looked up in the working directory: a server started inside someone else's project must not take their settings. A .env there is read only when you name it (--env-path=./.env).

Whichever file is chosen is read and written back with a renewed token, whatever --unsafe says. A destination is read once per process: a change to its .env from outside takes effect on restart. .env and environment variables hold secrets and the session; a YAML config file holds configuration only and refuses a secret-looking key.

Example .env file:

SAP_URL=https://your-sap-system.exampleSAP_CLIENT=100SAP_AUTH_TYPE=basicSAP_USERNAME=your-usernameSAP_PASSWORD=your-password

For a JWT you already hold (SAP BTP):

SAP_URL=https://your-btp-system.exampleSAP_CLIENT=100SAP_AUTH_TYPE=jwtSAP_GRANT_TYPE=noneSAP_JWT_TOKEN=your-jwt-token

For RFC connection:

SAP_URL=http://your-onprem-system.example:8000SAP_CLIENT=100SAP_AUTH_TYPE=basicSAP_USERNAME=your-usernameSAP_PASSWORD=your-passwordSAP_CONNECTION_TYPE=rfc

SAP_CONNECTION_TYPE=rfc in the --env / --env-path .env selects RFC, as do --connection-type=rfc, the process environment and YAML connection-type: rfc. Precedence: CLI, then the process environment (which the .env value joins, never over one already set), then YAML. Over RFC the host comes from SAP_URL and the system number from its port (80NN → NN); a port that follows no such rule needs SAP_SYSNR in the process environment. See RFC Setup Guide for prerequisites (SAP NW RFC SDK, a C++ toolchain, SAPNWRFC_HOME before the install).

For SNC (passwordless logon over RFC, no user or password):

SAP_URL=http://your-onprem-system.example:8000SAP_CLIENT=100SAP_CONNECTION_TYPE=rfcSAP_AUTH_TYPE=sncSAP_SNC_PARTNERNAME='p:CN=<system>, O=<org>, C=<country>'# Creates need a responsible person; over SNC no login is knownSAP_RESPONSIBLE=<your ABAP user># Optional: SAP_SNC_QOP, SAP_SNC_LIB, SAP_SNC_MYNAME

The credential of the installed SNC product (for example a Secure Login Client) is mapped to an ABAP user by its SNC name. SAP_CONNECTION_TYPE=rfc (or --connection-type=rfc) is required: SNC logs on over RFC only, and an SNC destination with HTTP is refused. SNC needs the SAP NW RFC SDK and @mcp-abap-adt/sap-rfc-lite, an optional dependency — see RFC Setup.

Not supported since 16.0: SAP_AUTH_TYPE=certificate and kerberos, saml, and a jwt grant other than authorization_code and none, in a .env or service key are refused at startup, naming the authentication (a saml destination with no grant: lacks: grantType). See the migration note for what to do instead.

Generate a .env (JWT):

# Install the CLI globally (one-time setup) — it ships mcp-auth and mcp-ssonpm install -g @mcp-abap-adt/auth-broker-cli
# Write a .env that states its authentication and grantmcp-auth generate-env --grant authorization_code   # `mcp-auth --help` lists the other flags

The .env states SAP_AUTH_TYPE and SAP_GRANT_TYPE; a jwt .env without a grant is refused at startup.

.env comments rule: only full-line comments are supported (lines that start with #).
Inline comments are not parsed, so keep comments on separate lines.

Claude recommendation: place the service key in the service-keys directory and use --mcp=<destination> (avoid manual JWT tokens).

Command-Line Options

Authentication:

• --mcp=<destination> - Named destination: service-keys/<destination>.json and sessions/<destination>.env, field by field
• --auth-broker-path=<path> - Custom path for auth-broker service keys and sessions
• --browser=<name> - Browser for a login: chrome, edge, firefox, system (default), headless, none
• --browser-auth-port=<port> - Browser login callback port, 1-65535 (default: 61001); an invalid value is refused at startup
• --allow-destination-header - Honour the x-mcp-destination header (HTTP/SSE only, off by default)
• --connection-type=<http|rfc> - SAP connection transport: http (default) or rfc
• --unsafe - Write named destinations' sessions to disk. By default they are kept in memory (one login per process). A .env you name is written back either way

When --mcp=<destination> is specified, automatic fallback loading of ./.env is skipped.

Examples:

# Named destination, session kept in memory (default)mcp-abap-adt --mcp=TRIAL
# Named destination, session persisted to sessions/TRIAL.envmcp-abap-adt --mcp=TRIAL --unsafe
# Custom base directory for service-keys/ and sessions/mcp-abap-adt --mcp=TRIAL --auth-broker-path=~/prj/tmp/ --unsafe
# Browser login on another callback portmcp-abap-adt --mcp=TRIAL --browser-auth-port=61005

See Client Configuration for complete configuration options.

Handler logging switches

• AUTH_LOG_LEVEL=error|warn|info|debug — sets base log level for handler logger; DEBUG_AUTH_LOG=true also enables debug.
• HANDLER_LOG_SILENT=true — fully disables handler logging.
• DEBUG_CONNECTORS=true — verbose connection logging in high-level handlers.
• DEBUG_HANDLERS=true — enables verbose logs for selected read-only/system handlers.

Development

Testing

npm test

Test logging switches

• TEST_LOG_LEVEL=error|warn|info|debug — controls test logger verbosity (DEBUG_TESTS/DEBUG_ADT_TESTS/DEBUG_CONNECTORS force debug).
• TEST_LOG_FILE=/tmp/adt-tests.log — writes test logs to a file (best-effort).
• TEST_LOG_SILENT=true — disables test logging pipeline (console output muted).
• TEST_LOG_COLOR=true — adds colored/prefixed tags to test log lines.
• All console.* in tests are routed through the test logger with a [test] prefix.

Building

npm run build

Developer Tools

# Generate tool documentationnpm run docs:tools
# See tools/README.md for more developer utilities

Contributors

Thank you to all contributors! See CONTRIBUTORS.md for the complete list.

Acknowledgment: This project was originally inspired by mario-andreschak/mcp-abap-adt. We started with the core concept and then evolved it into an independent project with our own architecture and features.

License

Two packages, two licences. Which one applies depends on which you install.

Both are published from this repository with one command, in the order the dependency requires:

npm run release:dry        # rehearses both, touches nothingnpm run release:publish    # @mcp-abap-adt/lib, then @mcp-abap-adt/core

release:publish skips a version already on the registry, so re-running after a failure resumes rather than starting over. It aborts on the first failure instead of publishing the server on top of a library that is not there.

Note that npm publish and npm run are different commands. npm publish release asks npm to publish a package named release, which is somebody else's package on the registry.

Copyright © 2025–2026 Oleksii Kyslytsia

Both are distributed in the hope that they will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

What this means. Running either, on your own data, carries no conditions.

Embedding the library in your own application carries no obligation to open your application: Apache-2.0 asks for the notice and the licence text to travel with it, and nothing more.

Distributing the standalone server, or running a modified version of it as a network service, means passing on the same freedoms under AGPL section 13 — including the source. That is why the two are separate packages: installing the library never puts the server in your dependency tree.

The packages underneath are LGPL-3.0-only — @mcp-abap-adt/adt-clients, adt-strategies, connection, logger, auth-broker, auth-providers, auth-stores and the contract packages interfaces-adt, interfaces-adt-connection, interfaces-network, interfaces-auth, interfaces-auth-sap and interfaces-utils — and the library links them at runtime. It was four of them when this paragraph was written; the rule is the whole scope now, libraries LGPL and servers AGPL or GPL, and the MIT that a few of the auth packages still carried was an oversight rather than an offer. LGPL does not reach your own code, but its terms do travel with those packages whatever this project is licensed as. Plan for that, not for the notice on this repository.

Other terms are possible. Apache-2.0 is what the library is offered under publicly, not the only way it can be offered. The copyright holder may license the same code separately to a party who needs different terms; that takes nothing away from anyone who received it under Apache-2.0, which is permanent. CONTRIBUTORS.md records what keeps that option open, including the rule that no LGPL code from the packages underneath is ever copied into this tree.

History. Releases through 8.13.0 were MIT and stay MIT; 9.x was GPL-3.0-only. A licence change is not retroactive — anyone may still take an earlier release under the licence it carried. See CONTRIBUTORS.md for the full account of how the relicensing was lawful.