Token metadata and URI in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Token metadata and URI

Token Created

↓

Assign Token ID

↓

Attach Metadata URI

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Metadata URI Points to JSON

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Client Fetches Metadata

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Display Token Info

This flow shows how a token is created with an ID, linked to a metadata URI, which points to JSON data that clients fetch to display token details.

Execution Sample

Blockchain / Solidity

function tokenURI(tokenId) {
  return baseURI + tokenId + '.json';
}

// Example: tokenURI(1) returns 'https://example.com/metadata/1.json'

This code returns the full URI for a token's metadata JSON file based on its ID.

Execution Table

Step	tokenId	baseURI	Computed URI	Action
1	1	'https://example.com/metadata/'	'https://example.com/metadata/1.json'	Concatenate baseURI + tokenId + '.json'
2	42	'https://example.com/metadata/'	'https://example.com/metadata/42.json'	Concatenate baseURI + tokenId + '.json'
3	100	'https://example.com/metadata/'	'https://example.com/metadata/100.json'	Concatenate baseURI + tokenId + '.json'
4	N/A	N/A	N/A	Stop - No more token IDs to process

💡 Execution stops after processing all requested token IDs.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
tokenId	N/A	1	42	100	N/A
baseURI	'https://example.com/metadata/'	'https://example.com/metadata/'	'https://example.com/metadata/'	'https://example.com/metadata/'	'https://example.com/metadata/'
Computed URI	N/A	'https://example.com/metadata/1.json'	'https://example.com/metadata/42.json'	'https://example.com/metadata/100.json'	N/A

Key Moments - 2 Insights

Why do we add '.json' at the end of the URI?

Because the metadata is stored in JSON files, adding '.json' tells the client to fetch the correct file format as shown in the execution_table rows 1-3.

What happens if the tokenId does not exist?

The function still returns a URI string, but the client may get an error or empty data when fetching, as the URI is constructed regardless of token existence (see execution_table step 4).

Visual Quiz - 3 Questions

Look at the execution_table, what is the Computed URI when tokenId is 42?

A 'https://example.com/metadata/42.json'

B 'https://example.com/metadata/1.json'

C 'https://example.com/metadata/100.json'

D 'https://example.com/metadata/42'

💡 Hint

Check the row where tokenId is 42 in the execution_table.

At which step does the execution stop according to the exit_note?

A After step 1

B After step 4

C After step 3

D After step 2

💡 Hint

Look at the exit_note and the last row in the execution_table.

If baseURI changes to 'https://newsite.com/data/', what will be the Computed URI for tokenId 1?

A 'https://newsite.com/data/1'

B 'https://example.com/metadata/1.json'

C 'https://newsite.com/data/1.json'

D 'https://example.com/data/1.json'

💡 Hint

Refer to how Computed URI is formed by concatenating baseURI + tokenId + '.json' in the variable_tracker.

Concept Snapshot

Token metadata URI:
- Each token has a unique ID.
- Metadata URI = baseURI + tokenId + '.json'
- URI points to JSON with token details.
- Clients fetch this URI to show info.
- URI is a string, independent of token existence.

Full Transcript

This visual execution trace shows how token metadata URIs are constructed in blockchain tokens. Starting from token creation, each token gets an ID. The tokenURI function concatenates a base URI string with the token ID and '.json' to form the full metadata URI. This URI points to a JSON file containing the token's metadata. The execution table traces this concatenation for token IDs 1, 42, and 100, showing the computed URIs. The variable tracker records how tokenId, baseURI, and the computed URI change step by step. Key moments clarify why '.json' is added and what happens if a token ID does not exist. The visual quiz tests understanding of URI formation and execution stopping points. The concept snapshot summarizes the key points for quick review.