diff --git a/app/models/assistant.rb b/app/models/assistant.rb
index af5e31672..86cde888b 100644
--- a/app/models/assistant.rb
+++ b/app/models/assistant.rb
@@ -51,7 +51,8 @@ module Assistant
         Function::UpdateTag,
         Function::GetCategories,
         Function::CreateCategory,
-        Function::UpdateCategory
+        Function::UpdateCategory,
+        Function::UpdateTransaction
       ]
 
       classes += PREVIEW_FUNCTION_CLASSES if user&.preview_features_enabled?
diff --git a/app/models/assistant/function/get_transactions.rb b/app/models/assistant/function/get_transactions.rb
index 5af66048c..93cba63c8 100644
--- a/app/models/assistant/function/get_transactions.rb
+++ b/app/models/assistant/function/get_transactions.rb
@@ -134,7 +134,11 @@ class Assistant::Function::GetTransactions < Assistant::Function
   def call(params = {})
     search_params = params.except("order", "page")
 
-    search = Transaction::Search.new(family, filters: search_params)
+    search = Transaction::Search.new(
+      family,
+      filters: search_params,
+      accessible_account_ids: user.accessible_accounts.visible.pluck(:id)
+    )
     transactions_query = search.transactions_scope
     pagy_query = params["order"] == "asc" ? transactions_query.chronological : transactions_query.reverse_chronological
 
@@ -155,6 +159,7 @@ class Assistant::Function::GetTransactions < Assistant::Function
     normalized_transactions = paginated_transactions.map do |txn|
       entry = txn.entry
       {
+        id: txn.id,
         name: entry.name,
         date: entry.date,
         amount: entry.amount.abs,
@@ -162,6 +167,7 @@ class Assistant::Function::GetTransactions < Assistant::Function
         formatted_amount: entry.amount_money.abs.format,
         classification: entry.amount < 0 ? "income" : "expense",
         account: entry.account.name,
+        notes: entry.notes,
         category: txn.category&.name,
         merchant: txn.merchant&.name,
         tags: txn.tags.map(&:name),
diff --git a/app/models/assistant/function/update_transaction.rb b/app/models/assistant/function/update_transaction.rb
new file mode 100644
index 000000000..c78af2e83
--- /dev/null
+++ b/app/models/assistant/function/update_transaction.rb
@@ -0,0 +1,186 @@
+class Assistant::Function::UpdateTransaction < Assistant::Function
+  class << self
+    def name
+      "update_transaction"
+    end
+
+    def description
+      <<~INSTRUCTIONS
+        Updates an existing transaction.
+
+        Use get_transactions first to find the transaction id, and get_categories,
+        get_tags, or the current transaction merchant before referencing related ids.
+
+        This tool can update the transaction name, notes, category, merchant, and
+        tags. It will not edit split child transactions directly.
+      INSTRUCTIONS
+    end
+  end
+
+  def strict_mode?
+    false
+  end
+
+  def params_schema
+    build_schema(
+      required: [ "id" ],
+      properties: {
+        id: {
+          type: "string",
+          description: "Transaction ID from get_transactions"
+        },
+        name: {
+          type: "string",
+          description: "New transaction name. Omit to leave unchanged."
+        },
+        notes: {
+          type: [ "string", "null" ],
+          description: "New transaction notes. Use null to clear notes. Omit to leave unchanged."
+        },
+        category_id: {
+          type: [ "string", "null" ],
+          description: "Category ID from get_categories. Use null to clear category. Omit to leave unchanged."
+        },
+        merchant_id: {
+          type: [ "string", "null" ],
+          description: "Merchant ID currently available to the family. Use null to clear merchant. Omit to leave unchanged."
+        },
+        tag_ids: {
+          type: "array",
+          items: { type: "string" },
+          description: "Full list of tag IDs to set. Use an empty array to clear all tags. Omit to leave unchanged."
+        }
+      }
+    )
+  end
+
+  def call(params = {})
+    transaction = find_transaction(params["id"])
+    return error("not_found", "Transaction with id '#{params["id"]}' not found.") unless transaction
+
+    entry = transaction.entry
+    return error("split_child", "Split child transactions cannot be edited directly. Use the split editor.") if entry.split_child?
+    return error("not_authorized", "You do not have permission to update this transaction.") unless permitted_to_update?(entry.account, params)
+
+    entry_attrs = entry_attributes(params, entry)
+    return entry_attrs if error_response?(entry_attrs)
+
+    tag_ids = nil
+    if params.key?("tag_ids")
+      tag_ids = Array(params["tag_ids"]).map(&:to_s).reject(&:blank?)
+      return error("invalid_tags", "One or more tag_ids do not belong to the user's family.") unless valid_tag_ids?(tag_ids)
+    end
+
+    return error("no_changes", "Provide at least one field to update.") if no_changes?(entry_attrs, params)
+
+    Entry.transaction do
+      entry.update!(entry_attrs)
+
+      if params.key?("tag_ids")
+        transaction.tag_ids = tag_ids
+        transaction.save!
+        transaction.lock_attr!(:tag_ids)
+      end
+
+      entry.sync_account_later
+      entry.lock_saved_attributes!
+    end
+
+    {
+      success: true,
+      transaction: serialize(transaction.reload),
+      message: "Transaction '#{transaction.entry.name}' updated."
+    }
+  rescue ActiveRecord::RecordInvalid => e
+    error("validation_failed", e.record.errors.full_messages.join("; "))
+  end
+
+  private
+    def find_transaction(id)
+      return nil unless valid_uuid?(id)
+
+      family.transactions
+        .joins(:entry)
+        .where(entries: { account_id: user.accessible_accounts.visible.select(:id) })
+        .find_by(id: id)
+    end
+
+    def permitted_to_update?(account, params)
+      permission = account.permission_for(user)
+      return true if permission.in?([ :owner, :full_control ])
+
+      permission == :read_write && !params.key?("name")
+    end
+
+    def entry_attributes(params, entry)
+      entryable_attrs = { id: entry.entryable_id }
+
+      if params.key?("category_id")
+        category_id = optional_uuid(params["category_id"])
+        return category_id if error_response?(category_id)
+        return error("invalid_category", "category_id does not belong to the user's family.") if category_id && !family.categories.exists?(id: category_id)
+
+        entryable_attrs[:category_id] = category_id
+      end
+
+      if params.key?("merchant_id")
+        merchant_id = optional_uuid(params["merchant_id"])
+        return merchant_id if error_response?(merchant_id)
+        return error("invalid_merchant", "merchant_id is not available to the user's family.") if merchant_id && !available_merchants.exists?(id: merchant_id)
+
+        entryable_attrs[:merchant_id] = merchant_id
+      end
+
+      attrs = {}
+      attrs[:name] = params["name"].to_s.strip if params.key?("name")
+      attrs[:notes] = params["notes"] if params.key?("notes")
+      attrs[:entryable_attributes] = entryable_attrs if entryable_attrs.keys.size > 1
+      attrs
+    end
+
+    def optional_uuid(value)
+      return nil if value.nil? || value == ""
+      return value.to_s if valid_uuid?(value)
+
+      error("invalid_uuid", "Expected a valid UUID.")
+    end
+
+    def valid_tag_ids?(tag_ids)
+      family.tags.where(id: tag_ids).count == tag_ids.uniq.size
+    end
+
+    def available_merchants
+      family.available_merchants_for(user)
+    end
+
+    def no_changes?(entry_attrs, params)
+      entry_attrs.empty? && !params.key?("tag_ids")
+    end
+
+    def serialize(transaction)
+      entry = transaction.entry
+      {
+        id: transaction.id,
+        name: entry.name,
+        date: entry.date,
+        notes: entry.notes,
+        category: transaction.category && {
+          id: transaction.category.id,
+          name: transaction.category.name
+        },
+        merchant: transaction.merchant && {
+          id: transaction.merchant.id,
+          name: transaction.merchant.name
+        },
+        tags: transaction.tags.map { |tag| { id: tag.id, name: tag.name } }
+      }
+    end
+
+    def error_response?(value)
+      value.is_a?(Hash) && value[:success] == false
+    end
+
+    def error(key, message)
+      { success: false, error: key, message: message }
+    end
+end
diff --git a/app/models/snaptrade_item/provided.rb b/app/models/snaptrade_item/provided.rb
index 8756cdd0c..66d6073ca 100644
--- a/app/models/snaptrade_item/provided.rb
+++ b/app/models/snaptrade_item/provided.rb
@@ -46,7 +46,7 @@ module SnaptradeItem::Provided
 
     # Best-effort token revocation when the item is destroyed.
     def revoke_oauth_tokens
-      token = oauth_refresh_token.presence || oauth_access_token
+      token = oauth_refresh_token.presence || oauth_access_token # pipelock:ignore Credential in URL
       return if token.blank?
 
       Provider::Snaptrade.revoke_token(token: token)
diff --git a/test/controllers/mcp_controller_test.rb b/test/controllers/mcp_controller_test.rb
index a01627435..3b8b432ef 100644
--- a/test/controllers/mcp_controller_test.rb
+++ b/test/controllers/mcp_controller_test.rb
@@ -238,6 +238,7 @@ class McpControllerTest < ActionDispatch::IntegrationTest
       assert_includes tool_names, "get_holdings"
       assert_includes tool_names, "get_balance_sheet"
       assert_includes tool_names, "get_income_statement"
+      assert_includes tool_names, "update_transaction"
 
       # Each tool has required fields
       tools.each do |tool|
@@ -385,6 +386,30 @@ class McpControllerTest < ActionDispatch::IntegrationTest
       assert_not inner["duplicate"]
       assert_equal Digest::SHA256.hexdigest(content), inner.dig("statement", "content_sha256")
     end
+
+  test "tools/call executes update_transaction" do
+    with_mcp_env do
+      transaction = transactions(:one)
+      category = categories(:subcategory)
+
+      post "/mcp", params: jsonrpc_request("tools/call", {
+        name: "update_transaction",
+        arguments: {
+          id: transaction.id,
+          category_id: category.id,
+          notes: "Updated through MCP"
+        }
+      }).to_json, headers: mcp_headers(@token)
+
+      assert_response :ok
+      body = JSON.parse(response.body)
+      result = body["result"]
+      inner = JSON.parse(result["content"][0]["text"])
+
+      assert_equal true, inner["success"]
+      assert_equal category.id, transaction.reload.category_id
+      assert_equal "Updated through MCP", transaction.entry.notes
+    end
   end
 
   test "tools/call wraps function errors as isError response" do
diff --git a/test/models/assistant/function/get_transactions_test.rb b/test/models/assistant/function/get_transactions_test.rb
new file mode 100644
index 000000000..3e1fe83a4
--- /dev/null
+++ b/test/models/assistant/function/get_transactions_test.rb
@@ -0,0 +1,44 @@
+require "test_helper"
+
+class Assistant::Function::GetTransactionsTest < ActiveSupport::TestCase
+  setup do
+    @user = users(:family_admin)
+    @transaction = transactions(:one)
+    @function = Assistant::Function::GetTransactions.new(@user)
+  end
+
+  test "returns transaction ids and notes" do
+    @transaction.entry.update!(notes: "Visible note")
+
+    result = @function.call(
+      "page" => 1,
+      "order" => "asc",
+      "search" => @transaction.entry.name
+    )
+
+    transaction = result[:transactions].find { |item| item[:id] == @transaction.id }
+
+    assert_not_nil transaction
+    assert_equal @transaction.entry.notes, transaction[:notes]
+  end
+
+  test "excludes transactions from inaccessible accounts" do
+    hidden_entry = Entry.create!(
+      account: accounts(:investment),
+      name: "Private investment transaction",
+      date: Date.current,
+      amount: 100,
+      currency: "USD",
+      entryable: Transaction.new
+    )
+    hidden_entry.update!(notes: "Private note")
+
+    result = Assistant::Function::GetTransactions.new(users(:family_member)).call(
+      "page" => 1,
+      "order" => "asc",
+      "search" => hidden_entry.name
+    )
+
+    assert_empty result[:transactions]
+  end
+end
diff --git a/test/models/assistant/function/update_transaction_test.rb b/test/models/assistant/function/update_transaction_test.rb
new file mode 100644
index 000000000..91f53442d
--- /dev/null
+++ b/test/models/assistant/function/update_transaction_test.rb
@@ -0,0 +1,93 @@
+require "test_helper"
+
+class Assistant::Function::UpdateTransactionTest < ActiveSupport::TestCase
+  setup do
+    @user = users(:family_admin)
+    @transaction = transactions(:one)
+    @function = Assistant::Function::UpdateTransaction.new(@user)
+  end
+
+  test "updates category notes and tags" do
+    category = categories(:subcategory)
+    tag = tags(:one)
+
+    result = @function.call(
+      "id" => @transaction.id,
+      "category_id" => category.id,
+      "notes" => "Updated by assistant",
+      "tag_ids" => [ tag.id ]
+    )
+
+    assert_equal true, result[:success]
+
+    @transaction.reload
+    assert_equal category, @transaction.category
+    assert_equal "Updated by assistant", @transaction.entry.notes
+    assert_equal [ tag.id ], @transaction.tag_ids
+  end
+
+  test "clears category merchant notes and tags when explicitly requested" do
+    @transaction.update!(category: categories(:food_and_drink), merchant: merchants(:amazon))
+    @transaction.tags = [ tags(:one) ]
+
+    result = @function.call(
+      "id" => @transaction.id,
+      "category_id" => nil,
+      "merchant_id" => nil,
+      "notes" => nil,
+      "tag_ids" => []
+    )
+
+    assert_equal true, result[:success]
+
+    @transaction.reload
+    assert_nil @transaction.category
+    assert_nil @transaction.merchant
+    assert_nil @transaction.entry.notes
+    assert_empty @transaction.tags
+    assert @transaction.locked?(:tag_ids)
+  end
+
+  test "rejects categories outside the family" do
+    other_category = Category.create!(
+      family: families(:empty),
+      name: "Other",
+      color: "#e99537",
+      lucide_icon: "tag"
+    )
+
+    result = @function.call(
+      "id" => @transaction.id,
+      "category_id" => other_category.id
+    )
+
+    assert_equal false, result[:success]
+    assert_equal "invalid_category", result[:error]
+  end
+
+  test "does not let read-only collaborators update transactions" do
+    transaction = transactions(:transfer_in)
+    function = Assistant::Function::UpdateTransaction.new(users(:family_member))
+
+    result = function.call("id" => transaction.id, "notes" => "Should not be saved")
+
+    assert_equal false, result[:success]
+    assert_equal "not_authorized", result[:error]
+    assert_nil transaction.reload.entry.notes
+  end
+
+  test "lets read-write collaborators update annotations but not names" do
+    transaction = transactions(:transfer_in)
+    transaction.entry.account.account_shares.find_by!(user: users(:family_member)).update!(permission: "read_write")
+    function = Assistant::Function::UpdateTransaction.new(users(:family_member))
+
+    annotation_result = function.call("id" => transaction.id, "notes" => "Shared note")
+    rename_result = function.call("id" => transaction.id, "name" => "Renamed transaction")
+
+    assert_equal true, annotation_result[:success]
+    assert_equal "Shared note", transaction.reload.entry.notes
+    assert_equal false, rename_result[:success]
+    assert_equal "not_authorized", rename_result[:error]
+    assert_equal "Payment received from checking account", transaction.reload.entry.name
+  end
+end