A Kavacha is nothing but a Stotra having a peculiar feature.

[Budha Kavacham][1] (found in Brahma Vaivarta Purana) starts as follows:

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> Asya **Budha kavacha stotra maha manthrasya**
> 
> For the chant called Armour for Budha (mercury)
> 
> Kasyapa Rishi
> 
> The sage is Sage Kasyapa
> 
> Anushtup Chanda
> 
> Meter is Anushtup
> 
> Budho Devatha
> 
> God is Budha (mercury)
> 
> Budha Preethyarthe Jape Viniyoga
> 
> This chant is being done to please God Budha.

<br>

As you can see, it says Budha Kavacha Stotra. That means Kavacha is a Stotra.

Similarly, the [Ketu Kavacham][2] (found in Brahmanda Purana) starts as follows:

<br>

>  अस्य **श्रीकेतुकवचस्तोत्**रमंत्रस्य त्र्यंबक ऋषिः I  अनुष्टप् छन्दः I
> केतुर्देवता I कं बीजं I नमः शक्तिः I  केतुरिति कीलकम् I
> केतुप्रीत्यर्थं जपे विनियोगः II 
> 
> Asya Sri Ketu-**kavacha-stotra**-mantrasya tryamabaka rishih,
> anushtupa chandaha, ketur devata etc....
<br>

So, again this also shows that Kavacha is actually a Stotra.

The peculiar feature of such Stotras are that they ask various deities to protect the various limbs of the chanter.

In the Budha Kavacha you will find that various names of Budha (like Rohini Suto, Khageswara etc. ) are requested to protect different body parts of the aspirant.

Similarly is composed the Ketu Kavacham or any other Kavacha-Stotra in general.


  [1]: http://www.hindupedia.com/en/Budha_Kavacham
  [2]: http://ioustotra.blogspot.com/2009/10/ketu-kavacham.html