diff --git a/Gemfile b/Gemfile
index abdc523db..c738837c1 100644
--- a/Gemfile
+++ b/Gemfile
@@ -59,6 +59,7 @@ gem 'net-imap', require: false # See https://github.com/mikel/mail/pull/1439
 gem 'net-pop', require: false # same
 gem 'net-smtp', require: false # same
 gem 'openid_connect'
+gem 'parsby'
 gem 'pg'
 gem 'phonelib'
 gem 'prawn-rails' # PDF Generation
diff --git a/Gemfile.lock b/Gemfile.lock
index 6423eaf0e..24ffb3357 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -467,6 +467,7 @@ GEM
       webfinger (>= 1.0.1)
     orm_adapter (0.5.0)
     parallel (1.22.1)
+    parsby (1.1.1)
     parser (3.1.2.0)
       ast (~> 2.4.1)
     pdf-core (0.9.0)
@@ -877,6 +878,7 @@ DEPENDENCIES
   net-pop
   net-smtp
   openid_connect
+  parsby
   pg
   phonelib
   prawn-rails
diff --git a/app/models/concerns/tags_substitution_concern.rb b/app/models/concerns/tags_substitution_concern.rb
index 72b5e415f..070f31ab3 100644
--- a/app/models/concerns/tags_substitution_concern.rb
+++ b/app/models/concerns/tags_substitution_concern.rb
@@ -4,6 +4,45 @@ module TagsSubstitutionConcern
   include Rails.application.routes.url_helpers
   include ActionView::Helpers::UrlHelper
 
+  module TagsParser
+    include Parsby::Combinators
+    extend self
+
+    def parse(io)
+      doc.parse io
+    end
+
+    define_combinator :doc do
+      many(tag | text) < eof
+    end
+
+    define_combinator :text do
+      join(many(any_char.that_fail(tag))).fmap do |str|
+        { text: str.force_encoding('utf-8').encode }
+      end
+    end
+
+    define_combinator :tag do
+      between(tag_delimiter, tag_delimiter, tag_text).fmap do |tag|
+        { tag: tag }
+      end
+    end
+
+    define_combinator :tag_delimiter do
+      lit('--')
+    end
+
+    define_combinator :tag_text do
+      join(many(any_char.that_fail(tag_delimiter | eol))).fmap do |str|
+        str.force_encoding('utf-8').encode
+      end
+    end
+
+    define_combinator :eol do
+      lit("\r\n") | lit("\n")
+    end
+  end
+
   DOSSIER_TAGS = [
     {
       libelle: 'motivation',
@@ -141,8 +180,6 @@ module TagsSubstitutionConcern
 
   SHARED_TAG_LIBELLES = (DOSSIER_TAGS + DOSSIER_TAGS_FOR_MAIL + INDIVIDUAL_TAGS + ENTREPRISE_TAGS + ROUTAGE_TAGS).map { |tag| tag[:libelle] }
 
-  TAG_DELIMITERS_REGEX = /--(?<capture>((?!--).)*)--/
-
   def tags
     if procedure.for_individual?
       identity_tags = INDIVIDUAL_TAGS
@@ -159,7 +196,7 @@ module TagsSubstitutionConcern
   end
 
   def used_type_de_champ_tags(text)
-    used_tags_for(text, with_libelle: true).filter_map do |(tag, libelle)|
+    used_tags_and_libelle_for(text).filter_map do |(tag, libelle)|
       if !tag.in?(SHARED_TAG_LIBELLES)
         if tag.start_with?('tdc')
           [libelle, tag.gsub('tdc', '').to_i]
@@ -170,19 +207,8 @@ module TagsSubstitutionConcern
     end
   end
 
-  def used_tags_for(text, with_libelle: false)
-    text, tags = normalize_tags(text)
-    text
-      .scan(TAG_DELIMITERS_REGEX)
-      .flatten
-      .map do |tag_str|
-        if with_libelle
-          tag = tags.find { |tag| tag[:id] == tag_str }
-          [tag_str, tag ? tag[:libelle] : nil]
-        else
-          tag_str
-        end
-      end
+  def used_tags_for(text)
+    used_tags_and_libelle_for(text).map { |(tag, _)| tag }
   end
 
   private
@@ -250,7 +276,7 @@ module TagsSubstitutionConcern
       return ''
     end
 
-    text, _ = normalize_tags(text)
+    tokens = parse_tags(text)
 
     tags_and_datas = [
       [champ_public_tags(dossier: dossier), dossier.champs],
@@ -259,51 +285,68 @@ module TagsSubstitutionConcern
       [ROUTAGE_TAGS, dossier],
       [INDIVIDUAL_TAGS, dossier.individual],
       [ENTREPRISE_TAGS, dossier.etablissement&.entreprise]
-    ]
+    ].filter_map do |(tags, data)|
+      data && [filter_tags(tags).index_by { _1[:id].presence || _1[:libelle] }, data]
+    end
 
-    tags_and_datas
-      .map { |(tags, data)| [filter_tags(tags), data] }
-      .reduce(text) { |acc, (tags, data)| replace_tags_with_values_from_data(acc, tags, data) }
-  end
-
-  def replace_tags_with_values_from_data(text, tags, data)
-    if data.present?
-      tags.reduce(text) do |acc, tag|
-        replace_tag(acc, tag, data)
+    tags_and_datas.reduce(tokens) do |tokens, (tags, data)|
+      # Replace tags with their value
+      tokens.map do |token|
+        case token
+        in { tag: _, id: id } if tags.key?(id)
+          { text: replace_tag(tags.fetch(id), data) }
+        in { tag: tag } if tags.key?(tag)
+          { text: replace_tag(tags.fetch(tag), data) }
+        else
+          token
+        end
       end
-    else
-      text
-    end
+    end.map do |token|
+      # Get tokens text representation
+      case token
+      in { tag: tag }
+        "--#{tag}--"
+      in { text: text }
+        text
+      end
+    end.join('')
   end
 
-  def replace_tag(text, tag, data)
-    libelle = Regexp.quote(tag[:id].presence || tag[:libelle])
-
-    # allow any kind of space (non-breaking or other) in the tag’s libellé to match any kind of space in the template
-    # (the '\\ |' is there because plain ASCII spaces were escaped by preceding Regexp.quote)
-    libelle.gsub!(/\\ |[[:blank:]]/, "[[:blank:]]")
-
+  def replace_tag(tag, data)
     if tag.key?(:target)
-      value = data.send(tag[:target])
+      data.public_send(tag[:target])
     else
-      value = instance_exec(data, &tag[:lambda])
+      instance_exec(data, &tag[:lambda])
     end
-
-    text.gsub(/--#{libelle}--/, value.to_s)
   end
 
-  def normalize_tags(text)
-    tags = types_de_champ_tags(procedure.types_de_champ_public_for_tags, Dossier::SOUMIS) + types_de_champ_tags(procedure.types_de_champ_private_for_tags, Dossier::INSTRUCTION_COMMENCEE)
-    [filter_tags(tags).reduce(text) { |text, tag| normalize_tag(text, tag) }, tags]
+  def procedure_types_de_champ_tags
+    filter_tags(types_de_champ_tags(procedure.types_de_champ_public_for_tags, Dossier::SOUMIS) + types_de_champ_tags(procedure.types_de_champ_private_for_tags, Dossier::INSTRUCTION_COMMENCEE))
   end
 
-  def normalize_tag(text, tag)
-    libelle = Regexp.quote(tag[:libelle])
+  def parse_tags(text)
+    tags = procedure_types_de_champ_tags.index_by { _1[:libelle] }
 
-    # allow any kind of space (non-breaking or other) in the tag’s libellé to match any kind of space in the template
-    # (the '\\ |' is there because plain ASCII spaces were escaped by preceding Regexp.quote)
-    libelle.gsub!(/\\ |[[:blank:]]/, "[[:blank:]]")
+    TagsParser.parse(text).map do |token|
+      case token
+      in { tag: tag } if tags.key?(tag)
+        { tag: tag, id: tags.fetch(tag).fetch(:id) }
+      else
+        token
+      end
+    end
+  end
 
-    text.gsub(/--#{libelle}--/, "--#{tag[:id]}--")
+  def used_tags_and_libelle_for(text)
+    parse_tags(text).filter_map do |token|
+      case token
+      in { tag: tag, id: id }
+        [id, tag]
+      in { tag: tag }
+        [tag]
+      else
+        nil
+      end
+    end
   end
 end
diff --git a/lib/tasks/benchmarks.rake b/lib/tasks/benchmarks.rake
index a8680b730..ec734a662 100644
--- a/lib/tasks/benchmarks.rake
+++ b/lib/tasks/benchmarks.rake
@@ -29,4 +29,28 @@ namespace :benchmarks do
       x.report("Démarche 55824") { PiecesJustificativesService.generate_dossier_export(p_55824.dossiers.limit(10_000)) }
     end
   end
+
+  desc 'Attestation Template parser'
+  task attestation_template_parser: :environment do
+    progress = ProgressReport.new(AttestationTemplate.count)
+    AttestationTemplate.find_each do |template|
+      parsed = TagsSubstitutionConcern::TagsParser.parse(template.body)
+      serialized = parsed.map do |token|
+        case token
+        in { tag: tag }
+          "--#{tag}--"
+        in { text: text }
+          text
+        end
+      end.join('')
+      if serialized != template.body
+        throw "Template '#{serialized}' is not eq '#{template.body}' with attestation template #{template.id}"
+      end
+      progress.inc
+    rescue => e
+      pp "Error with attestation template #{template.id}"
+      throw e
+    end
+    progress.finish
+  end
 end
diff --git a/spec/models/concern/tags_substitution_concern_spec.rb b/spec/models/concern/tags_substitution_concern_spec.rb
index b098fbaa7..eafed63d1 100644
--- a/spec/models/concern/tags_substitution_concern_spec.rb
+++ b/spec/models/concern/tags_substitution_concern_spec.rb
@@ -383,13 +383,13 @@ describe TagsSubstitutionConcern, type: :model do
 
     context 'when generating a document for a dossier that is not termine' do
       let(:dossier) { create(:dossier) }
-      let(:template) { '--motivation-- --date de décision--' }
+      let(:template) { 'text --motivation-- --date de décision--' }
       let(:state) { Dossier.states.fetch(:en_instruction) }
 
       subject { template_concern.send(:replace_tags, template, dossier) }
 
       it "does not treat motivation or date de décision as tags" do
-        is_expected.to eq('--motivation-- --date de décision--')
+        is_expected.to eq('text --motivation-- --date de décision--')
       end
     end
 
@@ -495,4 +495,19 @@ describe TagsSubstitutionConcern, type: :model do
 
     it { is_expected.to eq([["public", procedure.draft_revision.types_de_champ.first.stable_id], ['yolo']]) }
   end
+
+  describe 'parser' do
+    it do
+      tokens = TagsSubstitutionConcern::TagsParser.parse("hello world --public--, --numéro du dossier--, un test--yolo-- encore du text\n---\n encore du text")
+      expect(tokens).to eq([
+        { text: "hello world " },
+        { tag: "public" },
+        { text: ", " },
+        { tag: "numéro du dossier" },
+        { text: ", un test" },
+        { tag: "yolo" },
+        { text: " encore du text\n" + "---\n" + " encore du text" }
+      ])
+    end
+  end
 end