The document you are reading now is targeted at developers wanting to use or contribute to the engine of Open Terms Archive. For a high-level overview of Open Terms Archive’s wider goals and processes, please read its public homepage.

Open Terms Archive Engine

This codebase is a Node.js module enabling downloading, archiving and publishing versions of documents obtained online. It can be used independently from the Open Terms Archive ecosystem.


Words in bold are business domain names.

Services have terms written in documents, contractual (Terms of Services, Privacy Policy…) or not (Community Guidelines, Deceased User Policy…), that can change over time. Open Terms Archive enables users rights advocates, regulatory bodies and interested citizens to follow the changes to these terms, to be notified whenever a new version is published, to explore their entire history and to collaborate in analysing them. This free and open-source engine is developed to support these goals.

Main concepts


Open Terms Archive is a decentralised system. It aims at enabling any entity to track terms on its own. To that end, the Open Terms Archive engine can be run on any server, thus making it a dedicated instance. An instance tracks terms within a single collection.

A collection is characterised by a scope across dimensions that describe the terms it tracks, such as language, jurisdiction and industry.

Example scope

The terms tracked in this collection are:

  • Of dating services used in Europe.
  • In the European Union and Switzerland jurisdictions.
  • In English, unless no English version exists, in which case the primary official language of the jurisdiction of incorporation of the service operator will be used.


In order to maximise discoverability, collaboration and political power, public collections are federated within a single ecosystem. This makes their data mutually discoverable and enables mutualising effort.

Terms types

To distinguish between the different terms of a service, each has a type, such as “Terms of Service”, “Privacy Policy”, “Developer Agreement”…

This type matches the topic, but not necessarily the title the service gives to it. Unifying the types enables comparing terms across services.

More information on terms types can be found in the dedicated repository. They are published on NPM under @opentermsarchive/terms-types, enabling standardisation and interoperability beyond the Open Terms Archive engine.


The terms that constitute a collection are defined in simple JSON files called declarations.

A declaration also contains some metadata on the service on which the terms apply.

Here is an example declaration tracking the Privacy Policy of Open Terms Archive:

  "name": "Open Terms Archive",
  "documents": {
    "Privacy Policy": {
      "fetch": "",
      "select": ".TextContent_textContent__ToW2S"

Add terms to a collection

Open Terms Archive acquires terms to deliver an explorable history of changes. This can be done in two ways:

  1. For the present and future, by tracking.
  2. For the past, by importing from an existing fonds such as ToSBack, the Internet Archive, Common Crawl or any other in-house format.

Tracking terms

In order to track the changes of terms, the engine records a snapshot of documents that contain them by fetching their web location several times a day. The engine then extracts a version from this snapshot by:

  1. Selecting the subset of the document (or documents) that contains the terms (instead of, e.g., navigation menus, footers, cookies banners…).
  2. Removing insignificant content, that is residual content in this subset that is not part of the terms (e.g. ads, illustrative pictures, internal navigation links…).
  3. Filtering noise that can emerge in the terms by preventing parts that change frequently from triggering false positives for changes (e.g. tracker identifiers in links, relative dates…). The engine can execute custom filters written in JavaScript to that end.

After these steps, if changes are spotted in the resulting terms, a new version is recorded.

Preserving snapshots enables recovering after the fact information potentially lost in the extraction step: if declarations were wrong, they can be maintained and corrected versions can be extracted from the original snapshots.

Importing terms

Existing fonds can be prepared for easier analysis by unifying their format to the Open Terms Archive dataset format. This unique format enables building interoperable tools, fostering collaboration across reusers. Such a dataset can be generated from versions alone. If snapshots and declarations can be retrieved from the fonds too, then a full-fledged collection can be created.

Use the engine

This documentation describes how to execute the engine independently from any specific instance. For other use cases, other parts of the documentation could be more relevant:


This module is tested to work across operating systems (continuous testing on UNIX, macOS and Windows).

A Node.js runtime is required to execute this engine.

Supported Node.js version can be found in the package.json file

Getting started

This engine is published as a module on NPM. The recommended install is as a dependency in a package.json file, next to a folder containing declaration files.

npm install --save @opentermsarchive/engine
mkdir declarations

In an editor, create the following declaration file in declarations/Open Terms Archive.json to track the terms of the Open Terms Archive website:

  "name": "Open Terms Archive",
  "documents": {
    "Privacy Policy": {
      "fetch": "",
      "select": ".TextContent_textContent__ToW2S"

In the terminal:

npx ota track

The tracked terms can be found in the data folder.

This quick example aimed at letting you try the engine quickly. Most likely, you will simply npm install from an existing collection, or create a new collection from the collection template.


Once the engine module is installed as a dependency within another module, the ota command with the following subcommands is available.

In these commands:

  • <service_id> is the case sensitive name of the service declaration file without the extension. For example, for Twitter.json, the service ID is Twitter.
  • <terms_type> is the property name used under the documents property in the declaration to declare a terms. For example, in the getting started declaration, the terms type declared is Privacy Policy.

ota track

npx ota track

Track the current terms of services according to provided declarations.

The declarations, snapshots and versions paths are defined in the configuration.

Note that the snapshots and versions will be recorded at the moment the command is executed, on top of the existing local history. If a shared history already exists and the goal is to add on top of it, that history has to be downloaded before executing that command.

Recap of available options
npx ota track --help
Track terms of specific services
npx ota track --services "<service_id>" ["<service_id>"...]
Track specific terms of specific services
npx ota track --services "<service_id>" ["<service_id>"...] --types "<terms_type>" ["<terms_type>"...]
Track terms four times a day
npx ota track --schedule

ota validate

npx ota validate [--services <service_id>...] [--types <terms_type>...]

Check that all declarations allow recording a snapshot and a version properly.

If one or several <service_id> are provided, check only those services.

Validate schema only
npx ota validate --schema-only [--services <service_id>...] [--types <terms_type>...]

Check that all declarations are readable by the engine.

Allows for a much faster check of declarations, but does not check that the terms are actually accessible.

If one or several <service_id> are provided, check only those services.

Validate modified terms only
npx ota validate --modified

Run ota validate only on files that have been modified in Git.

ota lint

npx ota lint [--services <service_id>...] [--fix] [--modified]

Test the the format of declarations’ normalisation.

Use --fix to automatically correct formatting mistakes and ensure that all declarations are standardised.

If one or several <service_id> are provided, check only those services.

ota dataset

Export the versions dataset into a ZIP file and publish it to GitHub releases.

The dataset title and the URL of the versions repository are defined in the configuration.

To export the dataset into a local ZIP file:

npx ota dataset [--file <filename>]

To export the dataset into a ZIP file and publish it on GitHub releases:

GITHUB_TOKEN=ghp_XXXXXXXXX npx ota dataset --publish

The GITHUB_TOKEN can also be defined in a .env file.

To export, publish the dataset and remove the local copy that was created after it has been uploaded:

GITHUB_TOKEN=ghp_XXXXXXXXX npx ota dataset --publish --remove-local-copy
Publish dataset on monday every week

To schedule export, publishing and local copy removal:

GITHUB_TOKEN=ghp_XXXXXXXXX npx ota dataset --schedule --publish --remove-local-copy

ota serve

npx ota serve

Start the collection Web API server.

The Web API will be available under http://localhost:<port>/<basePath>/<apiVersion>/<resource>. The server <port> and <basePath> are defined in the configuration.

For example, with the default configuration, the list of services can be found at http://localhost:3000/api/v1/services.


Configuration file

The default configuration can be found in config/default.json. The full reference is given below. You are unlikely to want to edit all of these elements.

  "services": {
    "declarationsPath": "Directory containing services declarations and associated filters"
  "recorder": {
    "versions": {
      "storage": {
        "<storage-repository>": "Storage repository configuration object; see below"
    "snapshots": {
      "storage": {
        "<storage-repository>": "Storage repository configuration object; see below"
  "fetcher": {
    "waitForElementsTimeout": "Maximum time (in milliseconds) to wait for elements to be present in the page when fetching document in a headless browser"
    "navigationTimeout": "Maximum time (in milliseconds) to wait for page to load",
    "language": "Language (in ISO 639-1 format) to pass in request headers"
  "notifier": { // Notify specified mailing lists when new versions are recorded
    "sendInBlue": { // SendInBlue API Key is defined in environment variables, see the “Environment variables” section below
      "updatesListId": "SendInBlue contacts list ID of persons to notify on terms updates",
      "updateTemplateId": "SendInBlue email template ID used for updates notifications"
  "logger": { // Logging mechanism to be notified upon error
    "smtp": {
      "host": "SMTP server hostname",
      "username": "User for server authentication" // Password for server authentication is defined in environment variables, see the “Environment variables” section below
    "sendMailOnError": { // Can be set to `false` if sending email on error is not needed
      "to": "The address to send the email to in case of an error",
      "from": "The address from which to send the email",
      "sendWarnings": "Boolean. Set to true to also send email in case of warning",
  "reporter": { // Reporter mechanism to create GitHub issues when terms content is inaccessible
    "githubIssues": {
      "repositories": {
        "declarations": "GitHub repository where to create issues; expected format: <owner>/<repository>",
        "versions": "GitHub repository of versions associated with the declarations; expected format: <owner>/<repository>",
        "snapshots": "GitHub repository of snapshots associated with the declarations; expected format: <owner>/<repository>"
  "dataset": { // Release mechanism to create dataset periodically
    "title": "Title of the dataset; recommended to be the name of the instance that generated it",
    "versionsRepositoryURL": "GitHub repository where the dataset will be published as a release; recommended to be the versions repository for discoverability and tagging purposes"
  "api": { // Collection metadata API
    "port": "The port number on which the API will listen for incoming requests",
    "basePath": "The base path for the API endpoints"

The default configuration is merged with (and overridden by) environment-specific configuration that can be specified at startup with the NODE_ENV environment variable. See node-config for more information about configuration files.

For development, in order to have a local configuration that overrides the existing config, it is recommended to create a config/development.json file.

Storage repositories

Two storage repositories are currently supported: Git and MongoDB. Each one can be used independently for versions and snapshots.

  "storage": {
    "git": {
      "path": "Versions database directory path, relative to the root of this project",
      "publish": "Boolean. Set to true to push changes to the origin of the cloned repository at the end of every run. Recommended for production only.",
      "snapshotIdentiferTemplate": "Text. Template used to explicit where to find the referenced snapshot id. Must contain a %SNAPSHOT_ID that will be replaced by the snapshot ID. Only useful for versions",
      "author": {
        "name": "Name to which changes in tracked terms will be credited",
        "email": "Email to which changes in tracked terms will be credited"
  "storage": {
    "mongo": {
      "connectionURI": "URI for defining connection to the MongoDB instance. See",
      "database": "Database name",
      "collection": "Collection name"

Environment variables

Environment variables can be passed in the command-line or provided in a .env file at the root of the repository. See .env.example for an example of such a file.

  • SMTP_PASSWORD: a password for email server authentication, in order to send email notifications.
  • SENDINBLUE_API_KEY: a SendInBlue API key, in order to send email notifications with that service.
  • GITHUB_TOKEN: a token with repository privileges to access the GitHub API.

If an outgoing HTTP/HTTPS proxy to access the Internet is required, it is possible to provide it through the HTTP_PROXY and HTTPS_PROXY environment variable.


Deployment recipes are available in a dedicated repository. Look at the README to know how to deploy the engine.


Getting a copy

In order to edit the code of the engine itself, an editable and executable copy is necessary.

First of all, follow the requirements above. Then, clone the repository:

git clone
cd engine

Install dependencies:

npm install


If changes are made to the engine, check that all parts covered by tests still work properly:

npm test

If existing features are changed or new ones are added, relevant tests must be added too.

Suggesting changes

To contribute to the core engine of Open Terms Archive, see the CONTRIBUTING file. You will need knowledge of JavaScript and Node.js.

Sponsorship and partnerships

Beyond individual contributions, we need funds and committed partners to pay for a core team to maintain and grow Open Terms Archive. If you know of opportunities, please let us know over email at contact@[project name without spaces].org!


The code for this software is distributed under the European Union Public Licence (EUPL) v1.2. In short, this means you are allowed to read, use, modify and redistribute this source code, as long as you as you credit “Open Terms Archive Contributors” and make available any change you make to it under similar conditions.

Contact the core team over email at contact@[project name without spaces].org if you have any specific need or question regarding licensing.