MSSQL Schema Compare by T SQL

I have 21 DBs on same server which are 'supposed' to have the same schema (limiting schema only to table schema as of now) but they don't. In the environment I am, I can not install any tool/applications as per the compliance rules. The only way I can think of, is to pull up the schema of all the 21 DBs in excel and compare but its tedious.

Can someone guide me in developing a T-SQL which can compare the schema for all 21 DBs and highlight the differences?

These are the columns I need: Table_Name ,Column Name, Data type, Max Length, is_nullable, is_replicated, Primary Key

The following T-sql pulls up this in information for me. I need some idea about how can I compare this information for 21 DBs

SELECT    a.name Table_Name, c.name 'Column Name',
     t.Name 'Data type',
     c.max_length 'Max Length',
     c.is_nullable,a.is_replicated ,
     ISNULL(i.is_primary_key, 0) 'Primary Key'
FROM    Sys.tables a inner join      sys.columns c
On A.object_id=C.object_id
INNER JOIN 
     sys.types t ON c.user_type_id = t.user_type_id
LEFT OUTER JOIN 
     sys.index_columns ic ON ic.object_id = c.object_id AND ic.column_id = c.column_id
LEFT OUTER JOIN 
     sys.indexes i ON ic.object_id = i.object_id AND ic.index_id = i.index_id
     Order by 1,2

I need a starting point

I have to do stuff like this all the time under similar constraints, including without the benefit of the professional tools designed for it. Here's one way:

First create a temp table to hold the table information:

CREATE TABLE #DbSchemas(
    DbName nvarchar(128) NULL,
    Table_Name sysname NOT NULL,
    [Column Name] sysname NULL,
    [Data type] sysname NOT NULL,
    [Max Length] smallint NOT NULL,
    is_nullable bit NULL,
    is_replicated bit NULL,
    [Primary Key] bit NOT NULL
)
GO

Then wrap the query you already have in the undocumented system procedure sp_MSforeachdb to execute it on each database, adding the results into the #DbSchemas table:

EXECUTE master.sys.sp_MSforeachdb 'USE [?];
    INSERT INTO #DbSchemas
    SELECT DB_NAME() DbName,   a.name Table_Name, c.name [Column Name],
         t.Name [Data type],
         c.max_length [Max Length],
         c.is_nullable,a.is_replicated ,
         ISNULL(i.is_primary_key, 0) [Primary Key]
    FROM    Sys.tables a inner join      sys.columns c
    On A.object_id=C.object_id
    INNER JOIN 
         sys.types t ON c.user_type_id = t.user_type_id
    LEFT OUTER JOIN 
         sys.index_columns ic ON ic.object_id = c.object_id AND ic.column_id = c.column_id
    LEFT OUTER JOIN 
         sys.indexes i ON ic.object_id = i.object_id AND ic.index_id = i.index_id
         Order by 1,2
    ;
';
go

Now you should be able to query the data from any database in the #DbSchemas table:

select * from #DbSchemas where Dbname = 'master'

Finally, to compare them you can use something like this:

SELECT  * FROM #DbSchemas s1
WHERE   DbName = 'msdb'
  AND NOT EXISTS(
    SELECT  * FROM #DbSchemas s2 
    WHERE   s2.DbName           = 'master'
      AND   s2.Table_Name       = s1.Table_Name
      AND   s2.[Column Name]    = s1.[Column Name]
      AND   s2.[Data type]      = s1.[Data type]
      AND   s2.[Max length]     = s1.[Max length]
      AND   s2.is_nullable      = s1.is_nullable
      AND   s2.is_replicated    = s1.is_replicated
      AND   s2.[Primary Key]    = s1.[Primary Key]
      )