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Legislation Editing Open Software (LEOS)

Legislation: drafting
Main research: December 2021


  1. What does it claim to do?
  2. Substantiation of claims & potential issues
  3. How might the end-user assess effectiveness?
  4. What form does it take?
  5. Is it currently in use?
  6. The creators
  7. Jurisdiction
  8. License

What does it claim to do?

Legislation Editing Open Software (LEOS) is a browser-based application for drafting legislation. It is designed to allow collaboration between drafters and reviewers, and to facilitate interoperability with other systems through use of the Akoma Ntoso standard for legislative documents.

Claimed essential features

  • Enables collaborative drafting of legislation.
  • Adapted to the EU’s Ordinary Legislative Procedure.
  • Aims to implement user-centric design in legislative drafting.

“LEOS is designed to help those involved in draſting legislation, which is usually part of a complex process, by facilitating efficient online collaboration. Comments, suggestions, version control, co-edition, everything is there.” (About LEOS; archived)

“The latest prototype supports the drafting of the ‘secondary’ legislation of the EU law which has to be adopted under the Ordinary Legislative Procedure. Therefore, it covers the writing of Proposals for Directive, Decision and Regulation submitted by the Commission to the Council and the Parliament.” (About LEOS; archived)

The project’s governance principles state that, in accordance with the Tallinn ministerial declaration on user-centricity principles for design and delivery of digital public services, one aim of the project’s modular structure is to “support the implementation of user-centricity principles for design” (LEOS Governance; archived). These principles include “accessibility, security, availability, usability, protection of personal data and privacy, etc.”

Claimed rationale and benefits

  • To enable best practice in legislative drafting.
  • Helps deliver several goals: cost efficiency, transparency, interoperability, automation.
  • Interconnects legal databases and improves search and cross-referencing between legislative instruments.
  • Provides a platform that caters for practices in different jurisdictions.

“… we first developed a better understanding of the way public administrations address the issue of drafting their legislations [sic], with a view to identify best practices, improvements and areas where common efforts and developments are possible. We also invested time on researching the best open standards and tools so that we could be cost efficient and deliver open source for our community.” (About LEOS; archived)

From ISA2: Open Source Software for Editing Legislation (archived)

  • “… save costs, improve efficiency and transparency, reduce time-to-market and ensure interoperability as handling legal documents and follow up of legal procedures can be automated;
  • “… experience, lessons learnt, specifications, tools and components are published as Open Source tools on the Joinup platform, and are reusable by any Member State or EU Institution;
  • “… more transparent document management procedures in European policy execution;
  • “… facilitate the interconnection of legal databases and the performance of search engines”
  • “… enable[s] automatic processing like detection of legal references from any legal text and interoperability between IT systems.”

“We learnt that there can be as many ways of drafting legislation as there are existing legal entities. Therefore, using best open standards and tools, we focused on delivering reusable fundamental building blocks for legislation drafting, that could fit in various cases.” (FAQs (‘6. How can we adapt the tool to national legislation as it looks relevant only in the EC context?’); archived)

Claimed design choices

  • Represents legislative documents using the Akoma Ntoso XML schema.
  • Restricts document structure to prevent drafting mistakes.

“Content is stored in an XML format, currently Akoma Ntoso V3.” (About LEOS; archived)

“Regarding the structure, that is where we aim to be as restrictive as possible and this is not because we are conservative, but because this helps the draſters follow the rules and avoid mistakes.” (About LEOS; archived)

  • Built around core generic ‘building blocks’ of legislative workflows, that can be customised for particular jurisdictions.

LEOS’ structure is built around ‘generic’ and ‘customisable’ elements (FAQs (‘6. How can we adapt the tool to national legislation as it looks relevant only in the EC context?’); archived). These are the “fundamental building blocks” referred to above:

  • Collaboration (generic): online collaboration with customisable end-user permission management, using Author, Contributor, and Reviewer roles
  • Structure (customisable): the European institutions’ legislative structure is the starting point, but this can be “changed to support your legislative tradition”
  • Review/Comments (generic): ability to add comments and suggestions
  • Versioning (generic): assists where “version management becomes complicated especially when there is the case of several editors”
  • Import (customisable): retrieve legislative texts from source repositories (e.g. the EU Official Journal) and convert into the internal format used by LEOS
  • Rich text (customisable): add “pictures, tables, mathematical formulas”.

Substantiation of claims & potential issues

  • Inherits the same risk as its underlying technology Akoma Ntoso: AKN’s default set of concepts may be inappropriate or insufficient for a specific jurisdiction or context of application. If left untailored, this could have implications if these are relied upon by other computational law systems that rely on document structure for their functionality (e.g. search).

The Application Architecture page (archived) provides a detailed description of how the system works. It covers the relationship between its front-end user interface (‘presentation tier’), back-end ‘business logic’ (‘business logic tier’), and sources of data (‘data tier’). It also sets out the external application programming interface (API) for integration with other systems, the deployment strategy, and the dependencies of the system’s various modules.

  • The system is written in Java.
  • LEOS brings together various third-party open-source libraries for e.g. text editing and annotation on the front-end, for managing data on the back-end, and for serving the application to the user’s web browser.

  • The Application Architecture page includes a useful infographic demonstrating the Model-View-Presenter (‘Data side’-‘Client side’-‘Server side’) design pattern (more on Wikipedia), which facilitates ‘separation of concerns’, i.e. modularity:

    LEOS architecture

Further infographics are provided, including (i) a more detailed version of the MVP Web Component Architecture, (ii) the relationships between user devices, the application server, and the data sources when the application is deployed, and (iii) the dependencies between the application’s various modules.

This video of the most recent release gives a useful overview of the application:


How might the end-user assess effectiveness?

The project’s Key Performance Indicators (KPIs) show that the system is in use for real Commission legislative work, increasing quarter-on-quarter from 1 instrument in Q4 2018 to 6 instruments in Q3 2021 (2016.38. Legislation Interoperability Tools – LEGIT: Effectiveness; archived).

Testimonials from officials in Member State legislative offices (LEOS under ‘Who is already using this solution?’; archived).

The code is open source and can be downloaded at Releases (archived).


What form does it take?




The system can be run standalone, but there is evidence of it being integrated in broader legislation workflows, e.g. in Spain (Interview with Carlos Fernandez (Jan 2020); archived). It has a RESTful API designed to facilitate integration in other systems (Application Architecture; archived).

“…we design with the goal of delivering re-usable building blocks so LEOS is released Open Source as we believe that some parts of it could be reused and adapted by some other Public Administration having similar needs” (LEOS Pilot 3.1.0; archived). For example, Spain has extended LEOS to provide PDF export, code it is contributing back to the core project (Interview with Carlos Fernandez (Jan 2020); archived).

The system has a plugin architecture which in principle allows for its extensibility (Application Architecture; archived).


Is it in current use?

LEOS is classified by the project as ‘Under development’ (About LEOS; archived).

According to the Commission’s KPIs for the ISA2 project, use of the application for drafting Acts has increased quarter-on-quarter since 1 in Q4 2018 to 6 in Q3 2021 (2016.38. Legislation Interoperability Tools – LEGIT: Effectiveness; archived).


The creators

Created by

In-house developers, Independent developers, Legal practitioners


The project was initiated as part of the ISA2 action in the European Commission, focused on interoperability in public administration (Decision 2015/2240; archived). ISA2 is led by the Commission’s Informatics Directorate-General (DIGIT).

The team is mainly based within the Commission, though it includes a number of external consultants too (Meet the team; archived).



Background of developers

European Union law (Ordinary Legislative Procedure)

Target jurisdiction

EU law (the tool was built for European Commission Ordinary Legislative Procedure) but it can be adapted to work with any drafting approach compatible with LegalDocML and Akoma Ntoso.

Some member states are already using it for domestic work, including Spain and Slovenia.

Target legal domains

All domains.



LEOS is licensed under the European Union Public Licence (EUPL) (LEOS; archived). This is a free and open-source software license, with reciprocity (copyleft) – any derivative works must be licensed in the same way.


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