What Does Your User Agent Say About You?


A user agent is a computer program representing a person, for example, a browser in a Web context.

Besides a browser, a user agent could be a bot scraping webpages, a download manager, or another app accessing the Web. Along with each request they make to the server, browsers include a self-identifying User-Agent HTTP header called a user agent (UA) string. This string often identifies the browser, its version number, and its host operating system.

Spam bots, download managers, and some browsers often send a fake UA string to announce themselves as a different client. This is known as user agent spoofing.

The user agent string can be accessed with JavaScript on the client side using the navigator.userAgent property.

A typical user agent string looks like this: "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:35.0) Gecko/20100101 Firefox/35.0".


User Agent String

Browser Data

Definition Of User Agent

Maria Johnson
• Tuesday, 05 July, 2022
• 18 min read

During the first browser war, many web servers were configured to send web pages that required advanced features, including frames, to clients that were identified as some version of Mozilla only. Other browsers were considered to be older products such as Mosaic, Cello, or Samba, and would be sent a bare-bones HTML document.

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Automated agents are expected to follow rules in a special file called robots.txt “. The popularity of various Web browser products has varied throughout the Web's history, and this has influenced the design of websites in such a way that websites are sometimes designed to work well only with particular browsers, rather than according to uniform standards by the World Wide Web Consortium (W3C) or the Internet Engineering Task Force (IETF).

Websites often include code to detect browser version to adjust the page design sent according to the user agent string received. Thus, various browsers have a feature to cloak or spoof their identification to force certain server-side content.

For example, the Android browser identifies itself as Safari (among other things) in order to aid compatibility. User agent sniffing is the practice of websites showing different or adjusted content when viewed with certain user agents.

An example of this is Microsoft Exchange Server 2003's Outlook Web Access feature. When viewed with Internet Explorer 6 or newer, more functionality is displayed compared to the same page in any other browsers.

Web browsers created in the United States, such as Netscape Navigator and Internet Explorer, previously used the letters U, I, and N to specify the encryption strength in the user agent string. Until 1996, when the United States government disallowed encryption with keys longer than 40 bits to be exported, vendors shipped various browser versions with different encryption strengths.

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^ a b RFC 3261, SIP: Session Initiation Protocol, IETF, The Internet Society (2002) ^ RFC 7231, Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content, IETF, The Internet Society (June 2014) ^ Net news Article Format. Browser Versions Carry 10.5 Bits of Identifying Information on Average “, Electronic Frontier Foundation, 27 January 2010.

I've been rejected until I come back with Netscape” ^ “Android Browser Reports Itself as Apple Safari”. ^ User Agent String explained: Android WebKit Browser”.

Mozilla/5.0 (Linux; U; Android 2.2; ends; HTC_DesireHD_A9191 Build/FRF91) Apple WebKit/533.1 (HTML, like Gecko) Version/4.0 Mobile Safari/533.1 ^ Emberton, Stephen. ^ “Chrome Phasing out Support for User Agent ".

While rendering engines and other technologies used to build user agents are not by themselves considered user agents, it is fundamental to user agent accessibility that these technologies support user agent requirements. In building an user agent the developer should fully understand the support for AAG 2.0 when selecting technologies.

The following tests can be used to determine if software qualifies as an user agent for the purposes of these guidelines. Sometimes abbreviated as UA, the user agent is a browser text string that is given to each website you visit.

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UA's contain information such as the browser version, compatibility, operating system, and any modifying plugins. Using this data, a website can assess the capabilities of your computer, optimizing a page's performance and display.

Mozilla/4.0 is used for historical reasons as stated by Microsoft, not to be confused with the variants of Mozilla browsers, such as Firefox. Noted user agent string with Internet Explorer can have multiple .NET versions.

In the past, different encryption versions had to be released for specific parts of the world because of laws in the United States. Below is additional information about each of the different versions of Microsoft Windows and their corresponding user agent string codes.

For example, the button at the beginning of this page uses JavaScript to display your user agent string. However, if you want to gather the information or manipulate the data, it would be better to use a server-side scripting language, such as Perl.

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The Chrome (or Chromium/Blink-based engines) user agent string is similar to Firefox’s. For compatibility, it adds strings like HTML, like Gecko and Safari.

The Opera browser is also based on the Blink engine, which is why it almost looks the same, but adds “Or/”. In this example, the user agent string is mobile Safari’s version.

In addition, a web application providing message management, composition, and reception functionality is sometimes considered an email client. In the first case, shared disk, a user logs on a server and runs an MA on that machine.

The MA reads messages from a conventionally formatted storage, typically box, within the user's HOME directory. The MTA uses a suitable mail delivery agent (MDA) to add messages to that storage, possibly in concurrence with the MA.

Webmail applications running on the relevant server can also benefit from direct disk access to the mail storage. On the one hand, the Post Office Protocol (POP) allows the client to download messages one at a time and only delete them from the server after they have been successfully saved on local storage.

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However, there is no provision for flagging a specific message as seen, answered, or forwarded, thus POP is not convenient for users who access the same mail from different machines or clients. IMAP features an idle extension for real time updates, providing faster notification than polling where long-lasting connections are feasible.

Client settings require the server's name or IP address, and the username and password for each remote incoming mailbox. Mugs responsibilities include proper formatting according to RFC 5322 for headers and body, and MIME for non-textual content and attachments.

To better assist the user with destination fields, many clients maintain one or more address books and/or are able to connect to an LDAP directory server. Client settings require the name or IP address of the preferred outgoing mail server, the port number (25 for MTA, 587 for MSA), and the username and password for the authentication, if any.

There is a non-standard port 465 for SSL encrypted SMTP sessions, that many clients and servers support for backward compatibility. Transport Layer Security encryption can be configured for the standard ports, if both the client and the server support it.

With no encryption, much like for postcards, email activity is plainly visible by any occasional eavesdropper. S/MIME employs a model based on a trusted certificate authority (CA) that signs users' public keys.

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Open PGP employs a somewhat more flexible web of trust mechanism that allows users to sign one another's public keys. Headers, including originator, recipients, and subject, remain in plain text....

Another important standard supported by most email clients is MIME, which is used to send binary file email attachments. RFC 5068, Email Submission Operations: Access and Accountability Requirements, provides a survey of the concepts of MTA, MSA, MDA, and MA.

Email servers and client use the following TCP port numbers by default, unless configured for specialized installations: Protocoluseplain text or encrypt sessions plain text sessions only encrypt sessions only POP3 incoming mail110995 IMAP4 incoming mail143993 SMTP outgoing mail25(unofficial ) 465 MSA outgoing mail587 HTTP webmail80443Note that while webmail obeys the earlier HTTP disposition of having separate ports for encrypt and plain text sessions, mail protocols use the START TLS technique, thereby allowing encryption to start on an already established TCP connection.

Webmail has several advantages which include the ability to send and receive email from anywhere using a single application: a web browser. Significant examples of email services which also provide the user a webmail interface are Hotmail, Gmail, AOL, and Yahoo.

To build your code or deploy your software using Azure Pipelines, you need at least one agent. Each time you run a pipeline, you get a fresh virtual machine.


Microsoft-hosted agents can run jobs directly on the VM or in a container. You can use self-hosted agents in Azure Pipelines or Team Foundation Server (TFS).

Self-hosted agents give you more control to install dependent software needed for your builds and deployments. Installing two or more agents may adversely affect performance and the result of your pipelines.

You can install the agent on Linux, macOS, or Windows machines. On macOS, you need to clear the special attribute on the download archive to prevent Gatekeeper protection from displaying for each assembly in the tar file when ./ is run.

This elasticity reduces your need to run dedicated agents all the time. You specify a virtual machine scale set, a number of agents to keep on standby, a maximum number of virtual machines in the scale set, and Azure Pipelines manages the scaling of your agents for you.

Microsoft provides a free tier of service by default in every organization that includes at least one parallel job. Starting with Azure DevOps Server 2019, you do not have to pay for self-hosted concurrent jobs in releases.

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The agent software automatically determines various system capabilities such as the name of the machine, type of operating system, and versions of certain software installed on the machine. Also, environment variables defined in the machine automatically appear in the list of system capabilities.

The system sends the job only to agents that have capabilities matching the demands specified in the pipeline. Navigate to your project and choose Settings (gear icon) > Agent Queues.

Navigate to your project and choose Settings (gear icon) > Agent Queues. Select the desired agent, and choose the Capabilities tab.

Select the desired agent, and choose the Capabilities tab. You can view the details of an agent, including its version, and system and user capabilities, by using the following AZ pipelines agent Azure CLI methods.

Accepted values: false, true include-assigned-request : Whether to include details about the agents' current work. Accepted values: false, true include-capabilities : Whether to include the agents' capabilities in the response.

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Accepted values: false, true include-last-completed-request : Whether to include details about the agents' most recent completed work. Required if not configured as default or picked up via git config.

You can configure the default subscription using AZ account set -s NAME_OR_ID. Example The following example lists all agents in pool ID: 4 in table format.

Accepted values: false, true include-assigned-request : Whether to include details about the agents' current work. Accepted values: false, true include-capabilities : Whether to include the agents' capabilities in the response.

Accepted values: false, true include-last-completed-request : Whether to include details about the agents' most recent completed work. Required if not configured as default or picked up via git config.

You can configure the default subscription using AZ account set -s NAME_OR_ID. You can also use --output table which returns an abbreviated version of the same information.

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The agent communicates with Azure Pipelines or TFS to determine which job it needs to run, and to report the logs and job status. This pull model allows the agent to be configured in different topologies as shown below.

Here is a common communication pattern between the agent and Azure Pipelines or TFS. This token is generated by Azure Pipelines/TFS for the scoped identity specified in the pipeline.

That token is short-lived and is used by the agent to access resources (for example, source code) or modify resources (for example, upload test results) on Azure Pipelines or TFS within that job. After the job is completed, the agent discards the job-specific OAuth token and goes back to checking if there is a new job request using the listener OAuth token.

The payload of the messages exchanged between the agent and Azure Pipelines/TFS are secured using asymmetric encryption. The server uses the public key to encrypt the payload of the job before sending it to the agent.

The agent decrypts the job content using its private key. This is how secrets stored in pipelines or variable groups are secured as they are exchanged with the agent.


An agent pool administrator joins the agent to an agent pool, and the credentials of the service account (for Windows) or the saved username and password (for Linux and macOS) are used to initiate communication with TFS. If your on-premises environments do not have connectivity to a Microsoft-hosted agent pool (which is typically the case due to intermediate firewalls), you'll need to manually configure a self-hosted agent on on-premises computer(s).

The agents must have connectivity to the target on-premises environments, and access to the Internet to connect to Azure Pipelines or Team Foundation Server, as shown in the following schematic. In addition, you must be a local administrator on the server in order to configure the agent.

Your agent can authenticate to Azure DevOps Server or TFS using one of the following methods: Generate and use a PAT to connect an agent with Azure Pipelines or TFS 2017 and newer.

The PAT must have Agent Pools (read, manage) scope (for a deployment group agent, the PAT must have Deployment group (read, manage) scope), and while a single PAT can be used for registering multiple agents, the PAT is used only at the time of registering the agent, and not for subsequent communication. For more information, see the Authenticate with a personal access token (PAT) section in the ,, or self-hosted agents articles.

Start Internet Information Services (IIS) Manager. Select your TFS site and make sure Windows Authentication is enabled with a valid provider such as NTL or Kerberos.

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Start Internet Information Services (IIS) Manager. Select your TFS site and make sure Windows Authentication is enabled with the Negotiate provider and with another method such as NTL or Kerberos.

After you've configured the agent, we recommend you first try it in interactive mode to make sure it works. These modes also ensure that the agent starts automatically if the machine is restarted.

When the agent is configured to run in this mode, the screen saver is also disabled. Some domain policies may prevent you from enabling auto-logon or disabling the screen saver.

In such cases, you may need to seek an exemption from the domain policy, or run the agent on a workgroup computer where the domain policies do not apply. There are security risks when you enable automatic logon or disable the screen saver because you enable other users to walk up to the computer and use the account that automatically logs on.

If you configure the agent to run in this way, you must ensure the computer is physically protected; for example, located in a secure facility. If you use Remote Desktop to access the computer on which an agent is running with auto-logon, simply closing the Remote Desktop causes the computer to be locked and any UI tests that run on this agent may fail.

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The choice of agent account depends solely on the needs of the tasks running in your build and deployment jobs. For example, to run tasks that use Windows authentication to access an external service, you must run the agent using an account that has access to that service.

However, if you are running UI tests such as Selenium or Coded UI tests that require a browser, the browser is launched in the context of the agent account. These accounts have restricted permissions and their passwords don't expire, meaning the agent requires less management over time.

We update the agent software every few weeks in Azure Pipelines. An upgrade is requested when a platform feature or one of the tasks used in the pipeline requires a newer version of the agent.

When your Azure DevOps Server or TFS server has a newer version of the agent, and that newer agent is only different in minor version, it can usually be automatically upgraded. An upgrade is requested when a platform feature or one of the tasks used in the pipeline requires a newer version of the agent.

You can do this easily from the Agent pools tab under your project collection. Your pipelines won't run until they can target a compatible agent.


Navigate to your project and choose Settings (gear icon) > Agent Queues. Navigate to your project and choose Settings (gear icon) > Agent Queues.

You can check this value against the latest published agent version. See Azure Pipelines Agent and check the page for the highest version number listed.

This configuration will override the default version that came with the server at the time of its release. Transfer the downloaded package files to each Azure DevOps Server Application Tier by using a method of your choice (such as USB drive, Network transfer, and so on).

Your Azure DevOps Server will now use the local files whenever the agents are updated. While it often takes just a few seconds for your job to be assigned to a Microsoft-hosted agent, it can sometimes take several minutes for an agent to be allocated depending on the load on our system.

This approach can work well for agents that run jobs that don't consume many shared resources. You might find that in other cases you don't gain much efficiency by running multiple agents on the same machine.

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For example, it might not be worthwhile for agents that run builds that consume much disk and I/O resources. You might also run into problems if parallel build jobs are using the same singleton tool deployment, such as NPM packages.

Computer mouse remote control virtual reality ATMs speedometer the old iPod click wheel Websites such as Airbnb, Dropbox and Virgin America display strong user interface design.

An increasing focus on creating an optimized user experience has led some to carve out careers as UI and UX experts. Certain languages, such as HTML and CSS, have been geared toward making it easier to create a strong user interface and experience.

Users relied on a keyboard and a set of commands to navigate exchanges of information with the computer. This command line interface led to one in which menus (lists of choices written in text) predominated.

Finally, the GUI arrived, originating mainly in Xerox's Palo Alto Research Center (PARC), adopted and enhanced by Apple and effectively standardized by Microsoft in its Windows operating systems. Elements of a GUI include such things as windows, pull-down menus, buttons, scroll bars and icons.


Other Articles You Might Be Interested In

01: What Is My Browser User Agent String
02: Whoishostingthis Tools User Agent
03: Android Chrome Change User Agent
04: Android Edge Change User Agent
05: Android Firefox User Agent String
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