The Wayback Machine - https://web.archive.org/web/20151028180006/https://dev.twitter.com/web/tweet-button/parameters

Tweet Button Parameter Reference

A Tweet Button supports pre-populating share text, hashtags, and a Twitter account reference. Associate related Twitter accounts to drive followers.

Tweet content parameters

text optional

Pre-populated text highlighted in the Tweet composer.

Example Value: custom share text

url optional

URL included with the Tweet.

Example Value: https://dev.twitter.com/web/tweet-button

hashtags optional

A comma-separated list of hashtags to be appended to default Tweet text.

Example Value: example,demo

via optional

Attribute the source of a Tweet to a Twitter username.

Appears appended to Tweet text as via @username. The Twitter account may appear in a list of recommended accounts to follow.

Example Value: twitterdev

Button display parameters

Customize your displayed Tweet Button size, Tweet count display, button alignment, and more.

These visual parameters do not apply to Web Intents, which are styled separately by implementing sites.

size optional

When set to large, display a larger version of the button. Set to l for iframe.

Example Value: large

align optional

Force align the button to the left or right of the generated iframe.

Default behavior: the Tweet button chooses the best alignment option for the widget’s language.

Example Value: right

count optional

When set to none, the number of Tweets including the specified URL will not be shown.

When set to vertical, the number of Tweets including the specified URL appears above the button.

Note: this parameter will have no effect after November 2015. A Tweet button will display similar to a none value. Read more on the developer forum.

Example Value: none

counturl optional

Explicitly define a canonical URI for aggregated Tweet count display.

Example Value: https://dev.twitter.com/

lang optional

A supported Twitter language code.

Loads text components in the specified language.

Example Value: es

dnt optional

When set to true, the Tweet and its embedded page do not influence Twitter targeting including suggested accounts.

Example Value: true

HTML data-* example

<a class="twitter-share-button"
  href="https://twitter.com/share" 
  data-size="large"
  data-url="https://dev.twitter.com/web/tweet-button"
  data-count-url="https://dev.twitter.com/web/tweet-button"
  data-via="twitterdev"
  data-related="twitterapi,twitter"
  data-hashtags="example,demo"
  data-text="custom share text">
Tweet
</a>

Iframe example

<iframe
  src="https://platform.twitter.com/widgets/tweet_button.html?size=l&url=https%3A%2F%2Fdev.twitter.com%2Fweb%2Ftweet-button&via=twitterdev&related=twitterapi%2Ctwitter&text=custom%20share%20text&hashtags=example%2Cdemo"
  width="140"
  height="28"
  title="Twitter Tweet Button"
  style="border: 0; overflow: hidden;">
</iframe>

JavaScript factory example

twttr.widgets.createShareButton(
  "https:\/\/dev.twitter.com\/web\/tweet-button",
  document.getElementById("tweet-container"),
  {
    size: "large",
    via: "twitterdev",
    related: "twitterapi,twitter",
    text: "custom share text",
    hashtags: "example,demo"
  }
);

Web Intent example

Tweet

<a href="https://twitter.com/share?
  url=https%3A%2F%2Fdev.twitter.com%2Fweb%2Ftweet-button&
  via=twitterdev&
  related=twitterapi%2Ctwitter&
  hashtags=example%2Cdemo&
  text=custom%20share%20text">
Tweet
</a>