diff --git a/README.md b/README.md
index b4e2b621..39a4d41a 100644
--- a/README.md
+++ b/README.md
@@ -198,10 +198,16 @@ Zips given arrays together with the given function.
 
 #### debounce
 
+Makes the function run after the given period of not being called. Useful to delay input submission for autocomplete etc.
+
 #### delay
 
+When awaited, delays the execution by the given number of milliseconds.
+
 #### sequence
 
+Runs the given tasks in a sequence.
+
 ### date
 
 #### byDateWithFallback
@@ -210,12 +216,18 @@ Zips given arrays together with the given function.
 
 #### dateDiff
 
+Calculates the difference in milliseconds between two dates.
+
 #### dateInRange
 
+Checks if provided date is within the range.
+
 #### dayRange
 
 #### daysInMonths
 
+Returns numbers of days in all months of the year having regard to leap year.
+
 #### daysInYear
 
 #### displayMonth
@@ -224,6 +236,8 @@ Zips given arrays together with the given function.
 
 #### endOfDay
 
+Calculates end of a day in provided date.
+
 #### formatDate
 
 #### formatDateTime
@@ -248,6 +262,8 @@ Zips given arrays together with the given function.
 
 #### monthNames
 
+Returns all months names.
+
 #### offsetByBit
 
 #### parseHourMinutePair
@@ -256,6 +272,8 @@ Zips given arrays together with the given function.
 
 #### startOfDay
 
+Calculates start of a day in provided date.
+
 #### subtractDays
 
 #### toDate
diff --git a/async/README.md b/async/README.md
index 0ea12fa9..e2381449 100644
--- a/async/README.md
+++ b/async/README.md
@@ -1,5 +1,11 @@
 # debounce
 
+Makes the function run after the given period of not being called. Useful to delay input submission for autocomplete etc.
+
 # delay
 
+When awaited, delays the execution by the given number of milliseconds.
+
 # sequence
+
+Runs the given tasks in a sequence.
diff --git a/async/debounce.md b/async/debounce.md
index dce82919..a34e4c1e 100644
--- a/async/debounce.md
+++ b/async/debounce.md
@@ -1 +1,3 @@
 # debounce
+
+Makes the function run after the given period of not being called. Useful to delay input submission for autocomplete etc.
diff --git a/async/delay.md b/async/delay.md
index 021604ae..da6fc617 100644
--- a/async/delay.md
+++ b/async/delay.md
@@ -1 +1,3 @@
 # delay
+
+When awaited, delays the execution by the given number of milliseconds.
diff --git a/async/sequence.js b/async/sequence.js
index be0ac9e2..09738849 100644
--- a/async/sequence.js
+++ b/async/sequence.js
@@ -1,13 +1,11 @@
 export default async tasks => {
   const results = tasks.map(() => undefined);
-  await tasks.reduce((chain, current, i) => {
-    return chain.then(() =>
-      current().then(x => {
-        results[i] = x;
+  await tasks.reduce(async (chain, current, i) => {
+    await chain;
+    const x = await current();
+    results[i] = x;
 
-        return x;
-      })
-    );
+    return x;
   }, Promise.resolve());
 
   return results;
diff --git a/async/sequence.md b/async/sequence.md
index a6fb8760..32faf064 100644
--- a/async/sequence.md
+++ b/async/sequence.md
@@ -1 +1,3 @@
 # sequence
+
+Runs the given tasks in a sequence.
diff --git a/date/README.md b/date/README.md
index 8c1e867e..08b92a1a 100644
--- a/date/README.md
+++ b/date/README.md
@@ -4,12 +4,18 @@
 
 # dateDiff
 
+Calculates the difference in milliseconds between two dates.
+
 # dateInRange
 
+Checks if provided date is within the range.
+
 # dayRange
 
 # daysInMonths
 
+Returns numbers of days in all months of the year having regard to leap year.
+
 # daysInYear
 
 # displayMonth
@@ -18,6 +24,8 @@
 
 # endOfDay
 
+Calculates end of a day in provided date.
+
 # formatDate
 
 # formatDateTime
@@ -42,6 +50,8 @@
 
 # monthNames
 
+Returns all months names.
+
 # offsetByBit
 
 # parseHourMinutePair
@@ -50,6 +60,8 @@
 
 # startOfDay
 
+Calculates start of a day in provided date.
+
 # subtractDays
 
 # toDate
diff --git a/date/dateDiff.json b/date/dateDiff.json
index c50775e0..b449bd97 100644
--- a/date/dateDiff.json
+++ b/date/dateDiff.json
@@ -1,6 +1,6 @@
 {
   "name": "dateDiff",
-  "description": "TODO: Fill short description here.",
+  "description": "Calculates the difference in milliseconds between two dates.",
   "signature": "TODO: Fill type signature here.",
   "examples": [
     {
diff --git a/date/dateDiff.md b/date/dateDiff.md
index a299ea56..e74d2aea 100644
--- a/date/dateDiff.md
+++ b/date/dateDiff.md
@@ -1 +1,3 @@
 # dateDiff
+
+Calculates the difference in milliseconds between two dates.
diff --git a/date/dateDiff.test.ts b/date/dateDiff.test.ts
index 7fd8c8bb..a650200e 100644
--- a/date/dateDiff.test.ts
+++ b/date/dateDiff.test.ts
@@ -3,7 +3,21 @@
 import dateDiff from "./dateDiff.ts";
 
 describe("dateDiff", () => {
-  it.skip("TODO", () => {
-    expect(dateDiff()).toBeDefined();
+  it("returns the difference of 24 hours in miliseconds", () => {
+    const firstDate = new Date("2019-12-18T12:00:00");
+    const secondDate = new Date("2019-12-17T12:00:00");
+
+    const dayInMiliseconds = 86400000;
+
+    expect(dateDiff(firstDate, secondDate)).toEqual(dayInMiliseconds);
+  });
+
+  it("returns 0 difference of eqact same dates", () => {
+    const firstDate = new Date("2019-10-10T10:00:00");
+    const secondDate = new Date("2019-10-10T10:00:00");
+
+    const noDifference = 0;
+
+    expect(dateDiff(firstDate, secondDate)).toEqual(noDifference);
   });
 });
diff --git a/date/dateDiff.ts b/date/dateDiff.ts
index 2e4d2ce6..aadcb67b 100644
--- a/date/dateDiff.ts
+++ b/date/dateDiff.ts
@@ -1,4 +1,4 @@
-export default (a, b) => {
+export default (a: string | Date, b: string | Date): number => {
   const d1 = new Date(a);
   const d2 = new Date(b);
 
diff --git a/date/dateInRange.json b/date/dateInRange.json
index 35f60ade..bf5236e3 100644
--- a/date/dateInRange.json
+++ b/date/dateInRange.json
@@ -1,6 +1,6 @@
 {
   "name": "dateInRange",
-  "description": "TODO: Fill short description here.",
+  "description": "Checks if provided date is within the range.",
   "signature": "TODO: Fill type signature here.",
   "examples": [
     {
diff --git a/date/dateInRange.md b/date/dateInRange.md
index 87f3e12c..226f3cc7 100644
--- a/date/dateInRange.md
+++ b/date/dateInRange.md
@@ -1 +1,3 @@
 # dateInRange
+
+Checks if provided date is within the range.
diff --git a/date/dateInRange.test.ts b/date/dateInRange.test.ts
index 0ba4939f..96ceba00 100644
--- a/date/dateInRange.test.ts
+++ b/date/dateInRange.test.ts
@@ -3,7 +3,23 @@
 import dateInRange from "./dateInRange.ts";
 
 describe("dateInRange", () => {
-  it.skip("TODO", () => {
-    expect(dateInRange()).toBeDefined();
+  it("provided date is within the day range", () => {
+    const startRangeDate = new Date("2019-05-28T12:00:00");
+    const endRangeDate = new Date("2019-05-29T12:00:00");
+    const dateToCheck = new Date("2019-05-28T24:00:00");
+
+    expect(dateInRange(startRangeDate, endRangeDate)(dateToCheck)).toEqual(
+      true
+    );
+  });
+
+  it("provided date is not within the year range", () => {
+    const startRangeDate = new Date("2018-05-28T12:00:00");
+    const endRangeDate = new Date("2019-05-29T12:00:00");
+    const dateToCheck = new Date("2017-05-28T24:00:00");
+
+    expect(dateInRange(startRangeDate, endRangeDate)(dateToCheck)).toEqual(
+      false
+    );
   });
 });
diff --git a/date/dateInRange.ts b/date/dateInRange.ts
index 29997ef7..cfed7428 100644
--- a/date/dateInRange.ts
+++ b/date/dateInRange.ts
@@ -1,4 +1,6 @@
-export default (from, to) => (date = new Date()) => {
+export default (from: string | Date, to: string | Date) => (
+  date = new Date()
+): boolean => {
   const dateTime = new Date(date).getTime();
   const fromTime = new Date(from).getTime();
   const toTime = new Date(to).getTime();
diff --git a/date/daysInMonths.json b/date/daysInMonths.json
index 054f2c19..bb1402f2 100644
--- a/date/daysInMonths.json
+++ b/date/daysInMonths.json
@@ -1,6 +1,6 @@
 {
   "name": "daysInMonths",
-  "description": "TODO: Fill short description here.",
+  "description": "Returns numbers of days in all months of the year having regard to leap year.",
   "signature": "TODO: Fill type signature here.",
   "examples": [
     {
diff --git a/date/daysInMonths.md b/date/daysInMonths.md
index 6257a25f..d91d7b5a 100644
--- a/date/daysInMonths.md
+++ b/date/daysInMonths.md
@@ -1 +1,3 @@
 # daysInMonths
+
+Returns numbers of days in all months of the year having regard to leap year.
diff --git a/date/daysInMonths.test.ts b/date/daysInMonths.test.ts
index bed95fea..3bd70300 100644
--- a/date/daysInMonths.test.ts
+++ b/date/daysInMonths.test.ts
@@ -3,7 +3,45 @@
 import daysInMonths from "./daysInMonths.ts";
 
 describe("daysInMonths", () => {
-  it.skip("TODO", () => {
-    expect(daysInMonths()).toBeDefined();
+  it("returns number of days in a months in a leap year", () => {
+    const leapYear = true;
+
+    const numberOfDaysInMonthsInLeapYear = [
+      31,
+      29,
+      31,
+      30,
+      31,
+      30,
+      31,
+      31,
+      30,
+      31,
+      30,
+      31
+    ];
+
+    expect(daysInMonths(leapYear)).toEqual(numberOfDaysInMonthsInLeapYear);
+  });
+
+  it("returns number of days in a months in a year", () => {
+    const leapYear = false;
+
+    const numberOfDaysInMonths = [
+      31,
+      28,
+      31,
+      30,
+      31,
+      30,
+      31,
+      31,
+      30,
+      31,
+      30,
+      31
+    ];
+
+    expect(daysInMonths(leapYear)).toEqual(numberOfDaysInMonths);
   });
 });
diff --git a/date/daysInMonths.ts b/date/daysInMonths.ts
index 2ad5657f..6a6b17b7 100644
--- a/date/daysInMonths.ts
+++ b/date/daysInMonths.ts
@@ -1,4 +1,4 @@
-export default leapYear => [
+export default (leapYear): number[] => [
   31,
   leapYear ? 29 : 28,
   31,
diff --git a/date/endOfDay.json b/date/endOfDay.json
index 3676c1c5..fbca114d 100644
--- a/date/endOfDay.json
+++ b/date/endOfDay.json
@@ -1,6 +1,6 @@
 {
   "name": "endOfDay",
-  "description": "TODO: Fill short description here.",
+  "description": "Calculates end of a day in provided date.",
   "signature": "TODO: Fill type signature here.",
   "examples": [
     {
diff --git a/date/endOfDay.md b/date/endOfDay.md
index e16e7108..878cd7ef 100644
--- a/date/endOfDay.md
+++ b/date/endOfDay.md
@@ -1 +1,3 @@
 # endOfDay
+
+Calculates end of a day in provided date.
diff --git a/date/endOfDay.test.ts b/date/endOfDay.test.ts
index d0fe743d..2e7ba82b 100644
--- a/date/endOfDay.test.ts
+++ b/date/endOfDay.test.ts
@@ -3,7 +3,22 @@
 import endOfDay from "./endOfDay.ts";
 
 describe("endOfDay", () => {
-  it.skip("TODO", () => {
-    expect(endOfDay()).toBeDefined();
+  const date = new Date("2018-12-31T13:54:33.232Z");
+
+  it("should handle timezone offsets", () => {
+    const localOffset = -180;
+
+    const end = endOfDay(date, localOffset);
+    const expectedUTC = new Date("2019-01-01T03:00:00.000Z");
+    const expectedLocal = new Date("2018-12-31T24:00:00.000-03:00");
+
+    expect(end).toEqual(expectedUTC);
+    expect(end).toEqual(expectedLocal);
+  });
+
+  it("should handle default local date time display", () => {
+    const localOffset = 0;
+
+    expect(endOfDay(date)).toEqual(endOfDay(date, localOffset));
   });
 });
diff --git a/date/endOfDay.ts b/date/endOfDay.ts
index 71f92a0f..54005c08 100644
--- a/date/endOfDay.ts
+++ b/date/endOfDay.ts
@@ -1,6 +1,10 @@
 import toLocalDateTime from "./toLocalDateTime";
 
-export default (date, timezoneOffset = 0, local = true) => {
+export default (
+  date: string | Date,
+  timezoneOffset = 0,
+  local = true
+): Date => {
   const newDate = new Date(date);
   newDate.setHours(24, 0, 0, 0);
 
diff --git a/date/monthNames.js b/date/monthNames.js
index c870f165..bfb0bc7e 100644
--- a/date/monthNames.js
+++ b/date/monthNames.js
@@ -1,4 +1,4 @@
-export default [
+export default () => [
   "January",
   "February",
   "March",
diff --git a/date/monthNames.json b/date/monthNames.json
index 31794929..fe7b6a5e 100644
--- a/date/monthNames.json
+++ b/date/monthNames.json
@@ -1,6 +1,6 @@
 {
   "name": "monthNames",
-  "description": "TODO: Fill short description here.",
+  "description": "Returns all months names.",
   "signature": "TODO: Fill type signature here.",
   "examples": [
     {
diff --git a/date/monthNames.md b/date/monthNames.md
index 30f0f68a..958ae407 100644
--- a/date/monthNames.md
+++ b/date/monthNames.md
@@ -1 +1,3 @@
 # monthNames
+
+Returns all months names.
diff --git a/date/monthNames.test.ts b/date/monthNames.test.ts
index 0a888d04..1abda834 100644
--- a/date/monthNames.test.ts
+++ b/date/monthNames.test.ts
@@ -3,7 +3,22 @@
 import monthNames from "./monthNames.ts";
 
 describe("monthNames", () => {
-  it.skip("TODO", () => {
-    expect(monthNames()).toBeDefined();
+  it("Returns all month names", () => {
+    const allMonthNames = [
+      "January",
+      "February",
+      "March",
+      "April",
+      "May",
+      "June",
+      "July",
+      "August",
+      "September",
+      "October",
+      "November",
+      "December"
+    ];
+
+    expect(monthNames()).toEqual(allMonthNames);
   });
 });
diff --git a/date/monthNames.ts b/date/monthNames.ts
index c870f165..909169e7 100644
--- a/date/monthNames.ts
+++ b/date/monthNames.ts
@@ -1,4 +1,4 @@
-export default [
+export default (): string[] => [
   "January",
   "February",
   "March",
diff --git a/date/startOfDay.json b/date/startOfDay.json
index 952fa86a..ef50d412 100644
--- a/date/startOfDay.json
+++ b/date/startOfDay.json
@@ -1,6 +1,6 @@
 {
   "name": "startOfDay",
-  "description": "TODO: Fill short description here.",
+  "description": "Calculates start of a day in provided date.",
   "signature": "TODO: Fill type signature here.",
   "examples": [
     {
diff --git a/date/startOfDay.md b/date/startOfDay.md
index e257769b..ca44b63a 100644
--- a/date/startOfDay.md
+++ b/date/startOfDay.md
@@ -1 +1,3 @@
 # startOfDay
+
+Calculates start of a day in provided date.
diff --git a/date/startOfDay.test.ts b/date/startOfDay.test.ts
index ca6f59c1..a0da3058 100644
--- a/date/startOfDay.test.ts
+++ b/date/startOfDay.test.ts
@@ -3,7 +3,22 @@
 import startOfDay from "./startOfDay.ts";
 
 describe("startOfDay", () => {
-  it.skip("TODO", () => {
-    expect(startOfDay()).toBeDefined();
+  const date = new Date("2018-12-31T13:54:33.232Z");
+
+  it("should handle timezone offsets", () => {
+    const localOffset = -300;
+
+    const start = startOfDay(date, localOffset);
+    const expectedUTC = new Date("2018-12-31T05:00:00.000Z");
+    const expectedLocal = new Date("2018-12-31T00:00:00.000-05:00");
+
+    expect(start).toEqual(expectedUTC);
+    expect(start).toEqual(expectedLocal);
+  });
+
+  it("should handle default local date time display", () => {
+    const localOffset = 0;
+
+    expect(startOfDay(date)).toEqual(startOfDay(date, localOffset));
   });
 });
diff --git a/date/startOfDay.ts b/date/startOfDay.ts
index 82289a4b..fb9c411c 100644
--- a/date/startOfDay.ts
+++ b/date/startOfDay.ts
@@ -1,6 +1,10 @@
 import toLocalDateTime from "./toLocalDateTime";
 
-export default (date, timezoneOffset = 0, local = true) => {
+export default (
+  date: string | Date,
+  timezoneOffset = 0,
+  local = true
+): Date => {
   const newDate = new Date(date);
   newDate.setHours(0, 0, 0, 0);