user1298: I was wondering how it is possible to actually validate if a certain Token is an NFT without having to inspect the code of the script which mints that Token? Only by checking if the current quantity is 1 will certainly not ensure that it won't be possible to mint more of that Token.

user1142: You can check the token policy for that. For most NFT projects you can look it up on https://pool.pm
A token policy can look like this:
{
  "scripts": [
    {
      "keyHash": "66833acfcf26d87e56bc829aa7bcef13295d4eee4d8b442175bd67a9",
      "type": "sig"
    },
    {
      "slot": 31882046,
      "type": "before"
    }
  ],
  "type": "all"
}

You can see the "slot": 31882046 and "type": "before" values which means tokens with this policy can only be minted before slot 31882046. To be sure that your NFT is unique, you can check that the quantity is 1 and the current slot of the blockchain is later than the one mentioned in the policy.
This policy is from the following NFT: https://pool.pm/1131301ad4b3cb7deaddbc8f03f77189082a5738c0167e1772233097.CardanoBits1947

1298: <p>I was wondering how it is possible to actually validate if a certain Token is an NFT without having to inspect the code of the script which mints that Token? Only by checking if the current quantity is 1 will certainly not ensure that it won't be possible to mint more of that Token.</p>
 1142: <p>You can check the token policy for that. For most NFT projects you can look it up on <a href="https://pool.pm" rel="noreferrer">https://pool.pm</a></p>
<p>A token policy can look like this:</p>
<pre><code>{
  &quot;scripts&quot;: [
    {
      &quot;keyHash&quot;: &quot;66833acfcf26d87e56bc829aa7bcef13295d4eee4d8b442175bd67a9&quot;,
      &quot;type&quot;: &quot;sig&quot;
    },
    {
      &quot;slot&quot;: 31882046,
      &quot;type&quot;: &quot;before&quot;
    }
  ],
  &quot;type&quot;: &quot;all&quot;
}
</code></pre>
<p>You can see the <code>&quot;slot&quot;: 31882046</code> and <code>&quot;type&quot;: &quot;before&quot;</code> values which means tokens with this policy can only be minted before slot 31882046. To be sure that your NFT is unique, you can check that the quantity is 1 and the current slot of the blockchain is later than the one mentioned in the policy.</p>
<p>This policy is from the following NFT: <a href="https://pool.pm/1131301ad4b3cb7deaddbc8f03f77189082a5738c0167e1772233097.CardanoBits1947" rel="noreferrer">https://pool.pm/1131301ad4b3cb7deaddbc8f03f77189082a5738c0167e1772233097.CardanoBits1947</a></p>
