diff --git a/README.md b/README.md
index 974f173..fd4d9b0 100644
--- a/README.md
+++ b/README.md
@@ -9,8 +9,10 @@
 ![Release on Homebrew](https://github.com/5amCurfew/xtkt/actions/workflows/release.yml/badge.svg)
 
 - [:computer: Installation](#computer-installation)
-- [:nut_and_bolt: Using with Singer.io Targets](#nut_and_bolt-using-with-singerio-targets)
 - [:floppy_disk: Metadata](#floppy_disk-metadata)
+- [:pencil: Catalog](#pencil-catalog)
+- [:clipboard: State](#clipboard-state)
+- [:nut_and_bolt: Using with Singer.io Targets](#nut_and_bolt-using-with-singerio-targets)
 - [:wrench: Config.json](#wrench-configjson)
 - [:rocket: Examples](#rocket-examples)
   * [Rick & Morty API](#rick-&-morty-api)
@@ -19,19 +21,19 @@
   * [File csv](#file-csv)
   * [File jsonl](#file-jsonl)
 
-**v0.2.1**
+**v0.3.0**
 
-`xtkt` ("extract") is a data extraction tool that follows the Singer.io specification. Supported sources include RESTful-APIs, csv and jsonl.
+`xtkt` ("extract") is a data extraction tool that follows the Singer.io specification. Supported sources include RESTful APIs, csv and jsonl.
 
 `xtkt` can be pipe'd to any target that meets the Singer.io specification but has been designed and tested for databases such as SQLite & Postgres. Each stream is handled independently and deletion-at-source is not detected.
 
-Extracted records are versioned, with new and updated data being treated as distinct records (with resulting keys `_sdc_natural_key` (unique key) and `_sdc_surrogate_key` (version key)). Only new and/or updated records are sent to be processed by your target.
+Extracted records are versioned, with new and updated data being treated as distinct records (with resulting keys `_sdc_natural_key` (unique key) and `_sdc_surrogate_key` (version key)). Only new and/or updated records are sent to be processed by your target. 
 
 Fields can be dropped from records prior to being sent to your target using the `records.drop_field_paths` field in your JSON configuration file (see examples below). This may be suitable for dropping redundant, large objects within a record.
 
 Fields can be hashed within records prior to being sent to your target using the `records.sensitive_field_paths` field in your JSON configuration file (see examples below). This may be suitable for handling sensitive data.
 
-Both integers and floats are sent as floats. All fields are considered `NULLABLE`. All fields when extracting from CSV are considered strings for now.
+Both integers and floats are sent as floats. All fields except the generated `_sdc_surrogate_key` field are considered `NULLABLE`.
 
 Schema detection is naive using the first non-null data type detected per field when generating the catalog.
 
@@ -54,6 +56,26 @@ Flags:
   -v, --version    version for xtkt
 ```
 
+### :floppy_disk: Metadata
+
+`xtkt` adds the following metadata to records
+
+* `_sdc_surrogate_key`: SHA256 of a record
+* `_sdc_natural_key`: the unique key identifier of the record at source
+* `_sdc_time_extracted`: a timestamp (R3339) at the time of the data extraction
+
+### :pencil: Catalog
+
+A [catalog](https://github.com/singer-io/getting-started/blob/master/docs/SPEC.md#catalog) is required for the extraction. Discovery of the catalog can be run using the `--discover` flag which creates the `<stream_name>_catalog.json` file. This can then be altered for the definition of the [*schema message*](https://github.com/singer-io/getting-started/blob/master/docs/SPEC.md#schema-message) sent to your target. Running `xtkt` in discovery will overwite the existing catalog.
+
+```bash
+$ xtkt config.json --discover
+```
+
+### :clipboard: State
+
+`xtkt` uses a state file to track the records processed for each stream. The state file is written to the current working directory and is named `<stream_name>_state.json` where the `bookmark` values are a list of `_sdc_surrogate_key` values already processed. This defines the *[state message](https://github.com/singer-io/getting-started/blob/master/docs/SPEC.md#state-message)* sent to your target.
+
 ### :nut_and_bolt: Using with [Singer.io](https://www.singer.io/) Targets
 
 Install targets (Python) in `_targets/` in virtual environments:
@@ -64,7 +86,7 @@ Install targets (Python) in `_targets/` in virtual environments:
   4. `deactivate`
 
 ```bash
-xtkt config.json | ./_targets/target-name/bin/target-name`
+xtkt config.json | ./_targets/target-name/bin/target-name` --config config_target.json
 ```
 
 For example:
@@ -72,36 +94,11 @@ For example:
 xtkt config.json | ./_targets/pipelinewise-target-postgres/bin/target-postgres -c config_target_postgres.json 
 ```
 
-I have been using [jq](https://github.com/stedolan/jq) to view `stdout` messages in development. For example:
+For debugging I suggest pipe'ing to [jq](https://github.com/stedolan/jq) to view `stdout` messages in development. For example:
 ```bash
 $ xtkt config.json 2>&1 | jq .
 ```
 
-`xtkt` can be used in a bash script to iterate over a template `config.json` file to create many data extractions. For example
-```bash
-#!/bin/bash
-
-# Loop from 2009 to 2019
-for year in {2009..2019}
-do
-    new_config="config_${year}.json"
-    sed "s/YYYY/${year}/g" config.json.template > $new_config
-    echo "Generated ${new_config}"
-    echo "Running xtkt on ${new_config}"
-    xtkt $new_config | ./_targets/target-name/bin/target-name -c config_target_name.json
-done
-
-rm -f state_* config_*
-```
-
-### :floppy_disk: Metadata
-
-`xtkt` adds the following metadata to records
-
-* `_sdc_surrogate_key`: SHA256 of a record
-* `_sdc_natural_key`: the unique key identifier of the record at source
-* `_sdc_time_extracted`: a timestamp (R3339) at the time of the data extraction
-
 ### :wrench: Config.json
 
 #### xtkt
@@ -303,6 +300,9 @@ Oauth authentication required, records returned immediately in an array, paginat
     "url": "_config_json/data.jsonl",
     "records": {
         "unique_key_path": ["id"],
+        "drop_field_paths": [
+            ["salary"]
+        ],
         "sensitive_field_paths": [
             ["location", "address"],
             ["age"]
diff --git a/cmd/extract.go b/cmd/extract.go
index f559036..440a06a 100644
--- a/cmd/extract.go
+++ b/cmd/extract.go
@@ -94,6 +94,9 @@ func extract(discover bool) error {
 		}
 	}
 
+	// /////////////////////////////////////////////////////////
+	// Extract using existing catalog
+	// /////////////////////////////////////////////////////////
 	if !discover {
 
 		schema := lib.ParsedCatalog.Streams[0].Schema
diff --git a/cmd/root.go b/cmd/root.go
index 893304b..0d65df0 100644
--- a/cmd/root.go
+++ b/cmd/root.go
@@ -10,9 +10,8 @@ import (
 	"github.com/spf13/cobra"
 )
 
-var version = "0.2.1"
+var version = "0.3.0"
 var discover bool = false
-var defaultConcurrency int = 1000
 
 func Execute() {
 	rootCmd.Flags().BoolVar(&discover, "discover", false, "run the tap in discovery mode, creating the catalog")
@@ -69,10 +68,5 @@ func parseConfigJSON(filePath string) (lib.Config, error) {
 		return cfg, fmt.Errorf("error parseConfigJson unmarshlling config.json: %w", jsonError)
 	}
 
-	// Check if MaxConcurrency field is nil, set it to the default value
-	if cfg.MaxConcurrency == nil {
-		cfg.MaxConcurrency = &defaultConcurrency
-	}
-
 	return cfg, nil
 }