Wanted to know if there is a way to identify all the custom fields of Leads database

Chethan refers to custom ​fields, ​not custom ​objects.​

The answer is certainly not to use the API, since it does not correctly distinguish between standard and custom fields, and does not show hidden fields.

The most inclusive list of standard fields that I know of is:

Company Info / Account Owner Email Address

Company Info / Account Owner First Name

Company Info / Account Owner Last Name

Company Info / Annual Revenue

Company Info / Billing Address

Company Info / Billing City

Company Info / Billing Country

Company Info / Billing Postal Code

Company Info / Billing State

Company Info / Company

Company Info / Company Notes

Company Info / Company SFDC Type

Company Info / External Company Id

Company Info / Industry

Company Info / Main Phone

Company Info / Marketo Data.com Id

Company Info / Marketo Data.com Status

Company Info / Num Employees

Company Info / Parent Company Name

Company Info / SFDC Account Num

Company Info / SFDC Type

Company Info / SIC Code

Company Info / Site

Company Info / Website

Lead Info / Acquisition Date

Lead Info / Acquisition Program Name

Lead Info / Address

Lead Info / Anonymous IP

Lead Info / Black Listed

Lead Info / Black Listed Cause

Lead Info / City

Lead Info / Cookies

Lead Info / Country

Lead Info / Created

Lead Info / Date of Birth

Lead Info / Department

Lead Info / Do Not Call

Lead Info / Do Not Call Cause

Lead Info / Do Not Call Reason

Lead Info / Email

Lead Info / Email Invalid

Lead Info / Email Invalid Cause

Lead Info / Email Suspended

Lead Info / Email Suspended At

Lead Info / Email Suspended Cause

Lead Info / External Sales Person Id

Lead Info / Fax

Lead Info / First

Lead Info / Full Name

Lead Info / Inferred City

Lead Info / Inferred Company

Lead Info / Inferred Country

Lead Info / Inferred Metropolitan Area

Lead Info / Inferred Phone Area Code

Lead Info / Inferred Postal Code

Lead Info / Inferred State Region

Lead Info / Is Anonymous

Lead Info / Is Customer

Lead Info / Is Partner

Lead Info / Job Title

Lead Info / Last

Lead Info / Lead Notes

Lead Info / Lead Owner Email Address

Lead Info / Lead Owner First Name

Lead Info / Lead Owner Job Title

Lead Info / Lead Owner Last Name

Lead Info / Lead Owner Phone Number

Lead Info / Lead Partition

Lead Info / Lead Revenue Cycle Model

Lead Info / Lead Revenue Stage

Lead Info / Marketing Suspended

Lead Info / Marketing Suspended Cause

Lead Info / Marketo Data.com Id

Lead Info / Marketo Data.com Status

Lead Info / Marketo Unique Code

Lead Info / Marketo Unique Name

Lead Info / Middle

Lead Info / Mobile

Lead Info / Original Referrer

Lead Info / Original Search Engine

Lead Info / Original Search Phrase

Lead Info / Original Source Info

Lead Info / Original Source Type

Lead Info / Person Notes

Lead Info / Phone

Lead Info / Postal Code

Lead Info / Priority

Lead Info / Rating

Lead Info / Registration Source Info

Lead Info / Registration Source Type

Lead Info / Relative Score

Lead Info / Relative Urgency

Lead Info / Role

Lead Info / SFDC Created Date

Lead Info / SFDC Id

Lead Info / SFDC Is Deleted

Lead Info / SFDC Type

Lead Info / Salutation

Lead Info / Score

Lead Info / Source

Lead Info / State

Lead Info / Status

Lead Info / Unsubscribed

Lead Info / Unsubscribed Cause

Lead Info / Unsubscribed Reason

Lead Info / Updated

Lead Info / Urgency

Opportunity Info / Amount

Opportunity Info / Close Date

Opportunity Info / Description

Opportunity Info / Expected Revenue

Opportunity Info / Fiscal

Opportunity Info / Fiscal Quarter

Opportunity Info / Fiscal Year

Opportunity Info / Forecast Category

Opportunity Info / Forecast Category Name

Opportunity Info / Has Opportunity Line Item

Opportunity Info / Is Closed

Opportunity Info / Is Won

Opportunity Info / Last Activity Date

Opportunity Info / Lead Source

Opportunity Info / Name

Opportunity Info / Next Step

Opportunity Info / Probability

Opportunity Info / Quantity

Opportunity Info / SFDC Created Date

Opportunity Info / Stage

Opportunity Info / Type