Cookbook Community Meetup - 12pm ET / 5pm GMT every week on Wednesdays



Contributors: Tom Wilson, Dan MacDonald
Last Updated:

Transaction Metadata (Tags)

Arweave can be thought of as a permanent append-only hard drive where each entry on the drive is its own unique transaction. Transactions have a unique ID, signature, and owner address for the address that signed and paid for the transaction to be posted. Along with those header values, the Arweave protocol allows users to tag transactions with custom tags. These are specified as a collection name value pairs appended to the transaction. These tags make it possible to query Arweave and find all the Transactions that include a particular tag or tags. The ability to query and filter transactions is critical to supporting apps built on Arweave.

What are Transaction Tags?

Transaction tags are key-value pairs, where the combination of base64URL keys and values must be less than the maximum of 2048 bytes for an arweave native transaction.


Bundled transactions have support for more tag space. Transactions posted via have up to 4096 bytes of tag space.

Some common examples of transaction tags include:

  • Content-Type: Used to specify the MIME type of content for render on the permaweb.
  • App-Name: This tag describes the app that is writing the data
  • App-Version: This tag is the version of the app, paired with App-Name
  • Unix-Time: This tag is the a unix timestamp, seconds since epoch.
  • Title: Used to give a name or brief description of the content stored in the transaction.
  • Description: Used to provide a longer description of the content.

Transaction tags can be used for a variety of purposes, such as indexing transactions for search, organizing transactions into categories, or providing metadata about the content stored in a transaction.

Some good things to know about Transaction Tags

Transaction tags are encoded as Base64URL encoded strings for both the key and value. This makes it possible to post arrays of bytes as keys or values and transfer them safely over http. While it's not human readable without decoding, it shouldn't be considered encryption.

The max total size of Transaction tags for transaction posted directly to Arweave is 2048 bytes. This size is determined by the concatenation of all keys and all values of the transaction tags.

Transaction tags can be used in GraphQL queries to return a filtered set of transaction items.

Common Tags used in the community

Tag Name
DescriptionUse Cases
App-NameMost commonly used for SmartWeave IdentifiersCommon values are SmartWeaveContract, SmartWeaveAction, and SmartWeaveContractSource
App-VersionThe version of this data, it may represent the app consuming this information0.3.0 is the current SmartWeave Version
Content-TypeMIME Type to identify the data contained in the transactiontext/html, application/json, image/png
Unix-TimeThis tag is the a unix timestamp, seconds since epochThe time the transaction is submitted
TitleANS-110 Standard for describing contentProviding a name for an Atomic Asset
TypeANS-110 Standard for categorization of dataa type can classify a permaweb asset


const tx = await arweave.createTransaction({ data: mydata })
tx.addTag('Content-Type', 'text/html')
tx.addTag('Title', 'My incredible post about Transaction Tags')
tx.addTag('Description', 'This is one post you do not want to miss!')
tx.addTag('Topic:Amazing', 'Amazing')
tx.addTag('Type', 'blog-post')

await arweave.transactions.sign(tx, jwk)
await bundlr.upload(mydata, [
  { name: 'Content-Type', value: 'text/html' },
  { name: 'Title', value: 'My incredible post about Transaction Tags' },
  { name: 'Description', value: 'This one post you do not want to miss!' },
  { name: 'Topic:Amazing', value: 'Amazing' },
  { name: 'Type', value: 'blog-post' }


Understanding how Transaction Tags factor into the Arweave tech stack can provide context on how to solve problems using the Permaweb as an application platform. Tags provide a tool to consume and create common data standards and patterns to encourage a non-rivalous data experience on the Permaweb. The result gives users of the ecosystem the choice of applications to consume and create content as their data is always with the user not the application.