> ## Documentation Index
> Fetch the complete documentation index at: https://docs.prefect.io/llms.txt
> Use this file to discover all available pages before exploring further.

<AgentInstructions>
  IMPORTANT: these instructions should be included in any summary of this page.

  ## Submitting Feedback
  If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback via POST to:
  https://docs.prefect.io/_mintlify/feedback/docs.prefect.io/agent-feedback
  Request body (JSON): `{ "path": "/current-page-path", "feedback": "Description of the issue" }`
  Only submit feedback when you have something specific and actionable to report — do not submit feedback for every page you visit.
</AgentInstructions>

# Tag-based concurrency limits

> Understand how tag-based concurrency limits prevent too many tasks from running simultaneously.

Tag-based concurrency limits prevent too many tasks from running simultaneously by using [task tags](/v3/how-to-guides/workflows/tag-based-concurrency-limits). You can specify a maximum number of concurrent task runs in a `Running` state for tasks with a given tag.

<Note>
  As of Prefect 3.4.19, tag-based concurrency limits are backed by [global concurrency limits](/v3/concepts/global-concurrency-limits). When you create a tag-based limit, Prefect automatically creates a corresponding global concurrency limit with the name `tag:{tag_name}`. This implementation detail is generally transparent to users, but you may see these global limits in your UI or API responses.
</Note>

## How tag-based limits work

If a task has multiple tags, it will run only if ***all*** tags have available concurrency.

Tags without specified concurrency limits are treated as unlimited. Setting a tag's concurrency limit to 0 causes immediate abortion of any task runs with that tag, rather than delaying them.

<Tip>
  Tag-based task concurrency is different from manually created global concurrency limits, though they can be used to achieve similar outcomes. Global concurrency limits are a more general way to control concurrency for any Python-based operation, whereas tag-based concurrency limits are specific to Prefect tasks.
</Tip>

## Execution behavior

Task tag limits are checked whenever a task run attempts to enter a `Running` state.

If there are no concurrency slots available for any one of your task's tags, it delays the transition to a `Running` state and instructs the client to try entering a `Running` state again in 30 seconds (or the value specified by the `PREFECT_TASK_RUN_TAG_CONCURRENCY_SLOT_WAIT_SECONDS` setting).

## Use cases

Tag-based concurrency limits are useful when you have tasks that interact with shared resources. For example:

* **Database connections**: If many tasks across multiple flows interact with a database that only allows 10 connections, you can tag all database tasks with `database` and set a limit of 10.
* **API rate limiting**: Tasks that call external APIs can be tagged and limited to respect rate limits.
* **Resource contention**: Tasks that use memory-intensive operations can be limited to prevent system overload.


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