DNR Converter

A TypeScript library that converts adblock-style filtering rules into rules compatible with Chrome's Declarative Net Request (DNR) API. It is designed for developers building Manifest V3 browser extensions that need to translate existing AdGuard or other adblock filter lists into the DNR format required by modern Chrome extensions.

• Key concepts
  • Supported rule types
• Installation
  • Peer dependencies
• API overview
  • IFilter
  • Filter
  • ConverterOptions
  • Simple flow: FilterConverter + Ruleset
  • Advanced flow: FilterConverter with withSourceMap: true + RulesetWithSourceMap
  • Compact ruleset file format
  • MetadataRuleset
  • isSafeRule(rule)
  • DNR_CONVERTER_VERSION
  • Network rule types
• CLI
  • Commands
  • Programmatic API
• Documentation

Key concepts

• Filter — an adblock filter list represented as an object with an id and text content. Each filter list (e.g. AdGuard Base, EasyList) becomes one Filter input.
• Declarative rule — a chrome.declarativeNetRequest.Rule object that the browser evaluates natively. The converter produces these from filter text.
• Source map — a mapping from each generated declarative rule back to its originating filter and rule index, enabling reverse lookup when a declarative rule fires.
• Rule safety — Chrome classifies DNR rules as safe (block, allow, allowAllRequests, upgradeScheme) or unsafe (redirect, modifyHeaders). The library exposes a helper to check safety.
• Converter options — limits and paths that control conversion output (maximum rule counts, resource paths for redirects).

Supported rule types

The converter supports virtually all adblock network rule modifiers. The known MV3 limitations (inherent to the Declarative Net Request API) are:

Supported modifiers (with MV3 notes):

• Basic blocking/allowing rules, $third-party, $domain (no regexps / .* TLDs), all content types ($script, $image, $stylesheet, etc.)
• $important, $match-case, $method, $to, $denyallow, $header (no regex values), $all
• $redirect — allowlist rules not supported
• $csp, $removeparam, $removeheader, $permissions — allowlist rules not supported; rules with identical conditions are combined only within the same filter, not across filters
• $urltransform — limited; complex transforms produce multiple declarative rules via pipeline stages
• $cookie — limited; only supported without parameters (bare $cookie)
• $badfilter — partial: does not handle $domain intersections correctly

Not yet supported / not convertible to DNR:

• $popup, $redirect-rule, $referrerpolicy — not yet implemented
• $replace, $jsonprune, $xmlprune, $hls, $network, DNS modifiers ($client, $dnsrewrite, $dnstype, $ctag) — not expressible in DNR; produce conversion errors and are skipped
• Exception modifiers $jsinject, $stealth, $urlblock, $genericblock — not yet implemented
• $webrtc — deprecated and not supported

For detailed conversion examples with output, see Conversion Examples.

Installation

# pnpm
pnpm install @adguard/dnr-converter

# yarn
yarn add @adguard/dnr-converter

# npm
npm install @adguard/dnr-converter

Peer dependencies

The package requires @adguard/re2-wasm (1.2.0) as a peer dependency for regex validation.

API overview

The library uses a single FilterConverter class with two conversion modes selected by the withSourceMap option:

IFilter

import type { IFilter } from '@adguard/dnr-converter';

Single interface used by both conversion flows:

Filter

The single concrete IFilter implementation shipped by the library supports two construction modes:

• Pre-loaded (new Filter(id, content: string)) — accepts the filter text directly as a string. getContent() resolves immediately; unloadContent() is a no-op. Use for simple conversion or when content is already in memory.

• Lazy-loaded (new Filter(id, source: () => Promise<string>)) — accepts an async callback that fetches the content on demand. Supports promise deduplication across concurrent callers, and unloadContent() releases the cached content. Use with withSourceMap: true (advanced mode).

import { Filter } from '@adguard/dnr-converter';

// Pre-loaded (simple mode)
const filter = new Filter(1, '||example.com^');

// Lazy-loaded (advanced mode with withSourceMap: true)
const lazyFilter = new Filter(1, async () => fetchFilterText());

ConverterOptions

import type { ConverterOptions } from '@adguard/dnr-converter';

Configuration for the conversion process:

Simple flow: FilterConverter + Ruleset

Use this flow when you only need DeclarativeRule[] output from plain filter text, without source maps or lazy loading.

import { FilterConverter, Filter } from '@adguard/dnr-converter';

const filter = new Filter(1, '||example.com^\n@@||example.com/path^');

const converter = new FilterConverter();
const [{ ruleset, errors, limitations }] = await converter.convert([filter]);

console.log(ruleset.getDeclarativeRules()); // DeclarativeRule[]
console.log(ruleset.getSafeRulesCount());    // 2
console.log(errors.length);                 // 0

Combine multiple filters into one ruleset:

const [{ ruleset }] = await converter.convert(
    [filter1, filter2],
    { combine: true },
);
// ruleset.getId() === FilterConverter.COMBINED_RULESET_ID

Serialize and restore:

const json = ruleset.serialize();   // JSON string of DeclarativeRule[]

const { Ruleset } = await import('@adguard/dnr-converter');
const restored = Ruleset.deserialize(ruleset.getId(), json);

Ruleset (returned by default, without withSourceMap) implements IRuleset:

Advanced flow: FilterConverter with withSourceMap: true + RulesetWithSourceMap

Use this mode in browser extension internals when you need source maps, $badfilter cross-filter application, serialization with hash maps, and lazy content loading. Pass withSourceMap: true in the options to get RulesetWithSourceMap results.

import { Filter, FilterConverter } from '@adguard/dnr-converter';

const filter = new Filter(1, async () => '||example.com^\n@@||example.com/path^');

const converter = new FilterConverter();
const [{ ruleset, errors }] = await converter.convert([filter], { withSourceMap: true });

const declarativeRules = await ruleset.getDeclarativeRules(); // Promise<DeclarativeRule[]>
const sources = await ruleset.getRulesById(declarativeRules[0].id);
console.log(sources[0].sourceRule); // '||example.com^'

Apply $badfilter from dynamic filters against static rule sets:

const [{ ruleset: dynamicRuleset }] = await converter.convert(
    [dynamicFilter],
    { withSourceMap: true },
);
const rulesToDisable = await converter.computeRulesToDisable(
    [dynamicRuleset],
    [staticRuleset],
);
// rulesToDisable: UpdateStaticRulesOptions[]

RulesetWithSourceMap (returned when withSourceMap: true) implements IRulesetWithSourceMap:

import type { ConversionResult } from '@adguard/dnr-converter';

Result returned by converter methods:

Compact ruleset file format

serializeCompact() and MetadataRuleset.serialize() write a JSON array of DNR rules. The array starts with one or more metadata rules: block rules whose condition.urlFilter is dummy.rule.adguard.com (they never match a request) and whose metadata value is { "chunk": "<fragment>" }. Joining the fragments in array order gives the serialized metadata. Every metadata value, including JSON escaping and the wrapper, is at most 65,536 UTF-8 bytes: Edge Add-ons rejects packages with larger values. The ordinary declarative rules follow the metadata rules.

A metadata rule is recognized by the marker urlFilter together with the metadata key. A converted rule for the host dummy.rule.adguard.com without a metadata key is an ordinary rule.

Metadata rules are static DNR rules: they count towards the static rule quota and get the smallest IDs not used by any other rule of the ruleset. Ordinary rule IDs are never changed.

[
    { "id": 1, "action": { "type": "block" }, "condition": { "urlFilter": "dummy.rule.adguard.com", "resourceTypes": ["xmlhttprequest"] }, "metadata": { "chunk": "{\"metadata\":{...},\"lazyMetadata\":{...},\"filterCon" } },
    { "id": 2, "action": { "type": "block" }, "condition": { "urlFilter": "dummy.rule.adguard.com", "resourceTypes": ["xmlhttprequest"] }, "metadata": { "chunk": "tent\":\"||example.com^\"}" } },
    { "id": 1234567, "action": { "type": "block" }, "condition": { "urlFilter": "||example.com^" } }
]

Read a filter ruleset file with parseCompactRuleset():

import { Filter, parseCompactRuleset, RulesetWithSourceMap } from '@adguard/dnr-converter';

const content = parseCompactRuleset('ruleset_1', JSON.parse(fileText));
content.metadata;           // SerializedRulesetData
content.lazyMetadata;       // SerializedRulesetLazyData
content.filterContent;      // original filter text
content.declarativeRules;   // ordinary DNR rules, without the metadata rules
content.metadataRulesCount; // number of metadata rules, for static rule quota accounting

// Build the rule set directly from the parsed content.
const ruleset = RulesetWithSourceMap.fromCompact('ruleset_1', content, [new Filter(1, content.filterContent)]);

fromCompact() validates metadata at once and the lazy metadata and ordinary rules on first load, with the same schemas as RulesetWithSourceMap.deserialize(). The rule set keeps the parsed content in memory for its whole lifetime; unloadContent() does not release it.

When the parts are stored as strings, for example in IndexedDB, load them lazily with deserialize() and build the rule set with fromDeserialized(), passing the stored metadataRulesCount:

const ruleset = RulesetWithSourceMap.fromDeserialized(
    await RulesetWithSourceMap.deserialize(id, rawData, loadLazyData, loadDeclarativeRules, filters),
    metadataRulesCount,
);

The reader takes only the leading run of metadata rules, joins them and parses the result once. It throws InvalidMetadataChunksError (with a rulesetId property) when the input is not an array, has no leading metadata rule, has a metadata rule without a string chunk, or when the joined fragments are not valid JSON.

MetadataRuleset

import { MetadataRuleset, METADATA_RULESET_ID } from '@adguard/dnr-converter';

A specialized ruleset that stores checksums and additional properties for a collection of DNR rule sets. It serializes in the compact ruleset file format: a JSON array that contains only metadata rules carrying { checksums, additionalProperties } in metadata.chunk fragments.

METADATA_RULESET_ID is the constant 0; the ruleset's string ID is always "ruleset_0".

Checksum methods:

Additional-property methods:

Serialization:

const meta = new MetadataRuleset();
meta.setChecksum('ruleset_1', 'abc123');
meta.setAdditionalProperty('version', '2.0');

const json = meta.serialize();
const restored = MetadataRuleset.deserialize(json);

console.log(restored.getChecksum('ruleset_1')); // "abc123"
console.log(restored.getAdditionalProperty('version')); // "2.0"

isSafeRule(rule)

import { isSafeRule } from '@adguard/dnr-converter';

// DeclarativeRule from the DNR API
const rule = {
    id: 2,
    priority: 1,
    action: { type: 'block' },
    condition: { urlFilter: 'example.com' },
};

isSafeRule(rule); // true — "block" is a safe action

Returns true if the declarative rule's action is one of the safe rule actions (block, allow, allowAllRequests, upgradeScheme). Useful for separating safe static rules from unsafe dynamic rules that require additional review.

DNR_CONVERTER_VERSION

import { DNR_CONVERTER_VERSION } from '@adguard/dnr-converter';

console.log(DNR_CONVERTER_VERSION); // e.g. "0.0.1"

A string constant with the current library version.

Network rule types

The package exports types related to network rule parsing and validation:

import {
    Rule,
    HttpHeaderMatcher,
    RuleDeclarativeValidator,
} from '@adguard/dnr-converter';

• Rule — parsed network rule with accessors for domains, resource types, methods, advanced modifier values, priority, and option flags. Create instances via Rule.createFromText(filterListId, index, text).
• HttpHeaderMatcher — type describing the parsed $header modifier value.
• RuleDeclarativeValidator — static helper that checks whether a Rule can be converted to a DNR rule. Call RuleDeclarativeValidator.shouldConvertRule(rule) — returns true if the rule is convertible, false if it should be silently skipped, or throws UnsupportedModifierError if the rule uses an unsupported modifier.

CLI

The package ships a dnr-converter command-line tool for converting filter lists to DNR rulesets and extracting filter content back from compiled rulesets.

Commands

convert

Converts AdGuard filter lists from a metadata directory into DNR rulesets.

dnr-converter convert \
  ./filters \
  ./resources \
  ./dist/rulesets

Arguments:

Options:

The filters.json metadata file must be an array of filter metadata objects each with at minimum filterId and name fields.

extract-filters

Extracts original filter list content that was embedded in compiled DNR rulesets by the convert command.

dnr-converter extract-filters \
  ./dist/rulesets \
  ./extracted-filters

Arguments:

Programmatic API

The CLI logic is also available as a programmatic API via the @adguard/dnr-converter/cli subpath export:

import { convertFilters, generateMD5Hash, type ConvertFiltersOptions } from '@adguard/dnr-converter/cli';

await convertFilters(
    './filters',
    './resources',
    './dist/rulesets',
    { debug: true, prettifyJson: true },
);

Documentation

• Changelog
• Development
• Migration from tsurlfilter
• Conversion Examples
• LLM agent rules