diff --git a/src/PostgREST/DbRequestBuilder.hs b/src/PostgREST/DbRequestBuilder.hs
index dcb05f3bb..3d8c34cca 100644
--- a/src/PostgREST/DbRequestBuilder.hs
+++ b/src/PostgREST/DbRequestBuilder.hs
@@ -1,3 +1,11 @@
+{-|
+Module      : PostgREST.DbRequestBuilder
+Description : PostgREST database request builder
+
+This module is in charge of building an intermediate representation(ReadRequest, MutateRequest) between the HTTP request and the final resulting SQL query.
+
+A query tree is built in case of resource embedding. By inferring the relationship between tables, join conditions are added for every embedded resource.
+-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE DuplicateRecordFields#-}
 {-# LANGUAGE LambdaCase #-}
diff --git a/src/PostgREST/DbStructure.hs b/src/PostgREST/DbStructure.hs
index a4af0c7da..36b27a986 100644
--- a/src/PostgREST/DbStructure.hs
+++ b/src/PostgREST/DbStructure.hs
@@ -1,3 +1,13 @@
+{-|
+Module      : PostgREST.DbStructure
+Description : PostgREST schema cache
+
+This module contains queries that target PostgreSQL system catalogs, these are used to build the schema cache(DbStructure).
+
+The schema cache is necessary for resource embedding, foreign keys are used for inferring the relationships between tables.
+
+These queries are executed once at startup or when PostgREST is reloaded.
+-}
 {-# LANGUAGE FlexibleContexts      #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE QuasiQuotes           #-}
diff --git a/src/PostgREST/Error.hs b/src/PostgREST/Error.hs
index f54a8e638..7aee67c5f 100644
--- a/src/PostgREST/Error.hs
+++ b/src/PostgREST/Error.hs
@@ -1,3 +1,7 @@
+{-|
+Module      : PostgREST.Error
+Description : PostgREST error HTTP responses
+-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 {-# LANGUAGE FlexibleInstances    #-}
 {-# LANGUAGE TypeSynonymInstances #-}
diff --git a/src/PostgREST/Middleware.hs b/src/PostgREST/Middleware.hs
index 76cbe2db3..80ef38454 100644
--- a/src/PostgREST/Middleware.hs
+++ b/src/PostgREST/Middleware.hs
@@ -1,3 +1,7 @@
+{-|
+Module      : PostgREST.Middleware
+Description : Sets the PostgreSQL GUCs, role, search_path and pre-request function. Validates JWT.
+-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE FlexibleContexts #-}
diff --git a/src/PostgREST/OpenAPI.hs b/src/PostgREST/OpenAPI.hs
index e64e59807..08dd0f38d 100644
--- a/src/PostgREST/OpenAPI.hs
+++ b/src/PostgREST/OpenAPI.hs
@@ -1,10 +1,14 @@
+{-|
+Module      : PostgREST.OpenAPI
+Description : Generates the OpenAPI output
+-}
 {-# LANGUAGE OverloadedStrings #-}
 
 module PostgREST.OpenAPI (
   encodeOpenAPI
-  , isMalformedProxyUri
-  , pickProxy
-  ) where
+, isMalformedProxyUri
+, pickProxy
+) where
 
 import           Control.Arrow               ((&&&))
 import           Control.Lens
diff --git a/src/PostgREST/Parsers.hs b/src/PostgREST/Parsers.hs
index a90689183..b5e601afa 100644
--- a/src/PostgREST/Parsers.hs
+++ b/src/PostgREST/Parsers.hs
@@ -1,3 +1,9 @@
+{-|
+Module      : PostgREST.Parsers
+Description : PostgREST parser combinators
+
+This module is in charge of parsing all the querystring values in an url, e.g. the select, id, order in `/projects?select=id,name&id=eq.1&order=id,name.desc`.
+-}
 module PostgREST.Parsers where
 
 import           Protolude                     hiding (try, intercalate, replace, option)
diff --git a/src/PostgREST/RangeQuery.hs b/src/PostgREST/RangeQuery.hs
index cd7ffc69b..4819d6d12 100644
--- a/src/PostgREST/RangeQuery.hs
+++ b/src/PostgREST/RangeQuery.hs
@@ -1,3 +1,7 @@
+{-|
+Module      : PostgREST.RangeQuery
+Description : Logic regarding the `Range` header and `limit`, `offset` querystring arguments.
+-}
 module PostgREST.RangeQuery (
   rangeParse
 , rangeRequested
diff --git a/src/PostgREST/Types.hs b/src/PostgREST/Types.hs
index c36c00385..44c88e449 100644
--- a/src/PostgREST/Types.hs
+++ b/src/PostgREST/Types.hs
@@ -1,3 +1,7 @@
+{-|
+Module      : PostgREST.Types
+Description : PostgREST common types and functions used by the rest of the modules
+-}
 {-# LANGUAGE DuplicateRecordFields    #-}
 module PostgREST.Types where
 import           Protolude