Migrating from 1.x to 2.x

slackblocks 2.0 is a major version bump that focuses on cleaning up internal correctness issues, modernising the type-annotation surface, and adding several ergonomic helpers. The good news: for almost all users, upgrading is a no-op beyond changing the Python version pin.

This page covers what actually changes for you and what's worth adopting once you've upgraded.

Quick checklist

Step	Action
1	Confirm you are on Python 3.10 or newer. If not, stay on `slackblocks ~= 1.2`.
2	Bump your dependency pin to `slackblocks ~= 2.0` (or `>=2,<3`).
3	Run your test suite. Existing code should continue to work unchanged.
4	Optionally adopt the new conveniences below.

Truly breaking changes

There is exactly one breaking change you might trip over:

Python 3.8 and 3.9 are no longer supported

Both reached upstream end of life (3.8 EOL Oct 2024, 3.9 EOL Oct 2025) and are not receiving security patches.

If you are still on either:

Stay on the 1.x line until you can upgrade Python. The 1.x line is maintained on a best-effort basis for bugfixes; see the Compatibility page.
Pin via your package manager:

pip (requirements.txt)poetry (pyproject.toml)uv (pyproject.toml)

slackblocks>=1,<2

slackblocks = "^1"

"slackblocks>=1,<2"

That's it for breaking changes. Nothing else in the public API was removed or renamed.

What's not breaking, but worth adopting

`PlainText` and `Markdown` instead of `Text(type_=...)`

Before:

from slackblocks import Text, TextType

heading = Text("Welcome", type_=TextType.PLAINTEXT, emoji=True)
body = Text("**bold**", type_=TextType.MARKDOWN, verbatim=True)

After:

from slackblocks import PlainText, Markdown

heading = PlainText("Welcome", emoji=True)
body = Markdown("**bold**", verbatim=True)

PlainText and Markdown are subclasses of Text, so anywhere a Text or TextLike was accepted before still accepts the new types. The rendered JSON is byte-identical to the equivalent Text calls.

`Workflow.from_url(...)` instead of nested `Workflow(trigger=Trigger(...))`

Before:

from slackblocks import Workflow, Trigger, InputParameter

workflow = Workflow(
    trigger=Trigger(
        url="https://slack.com/shortcuts/...",
        customizable_input_parameters=[
            InputParameter(name="env", value="prod"),
            InputParameter(name="retries", value="3"),
        ],
    ),
)

After:

from slackblocks import Workflow

workflow = Workflow.from_url(
    "https://slack.com/shortcuts/...",
    env="prod",
    retries="3",
)

The verbose form continues to work, so you do not have to migrate.

`block_kit_builder_url(...)` for browser preview

New helper that turns any block, list of blocks, message, view, or raw dict into a Block Kit Builder URL. Open the URL in your browser to see exactly what Slack will render before you ship.

from slackblocks import SectionBlock, block_kit_builder_url

print(block_kit_builder_url(SectionBlock("Hi")))
# https://app.slack.com/block-kit-builder/#%7B%22blocks%22%3A%5B...%5D%7D

Pass team_id="T0123ABCD" for a workspace-specific URL.

Typed exceptions for finer-grained error handling

InvalidUsageError now has five subclasses, raised in well-defined situations:

Subclass	Raised when
`LengthError`	A string or list violates a min/max-length constraint.
`RangeError`	A numeric value violates a min/max-value constraint.
`TypeMismatchError`	Wrong type or unexpected discrete value.
`MutualExclusivityError`	Two args that must not both be set were both set.
`MissingRequiredError`	At least one of a set of args was required.

from slackblocks import Button, LengthError

try:
    Button(text="x" * 100, action_id="b")
except LengthError as e:
    # specifically a length violation
    handle_length(e)

Existing except InvalidUsageError blocks continue to catch every subclass — no change required to upgrade. The new subclasses are purely additive.

Round-tripping incoming Slack JSON with `from_dict`

If your app receives Slack interactivity payloads or events and wants to inspect the blocks, you can now parse them back into slackblocks objects:

import json
from slackblocks import Block

incoming = json.loads(slack_request_body)
block = Block.from_dict(incoming["blocks"][0])
print(block.text.text)  # for a SectionBlock, etc.

Block.from_dict reads data["type"] and dispatches to the right subclass. Composition objects (Text, Option, Confirm, etc.) and the simple blocks (DividerBlock, FileBlock, HeaderBlock, MarkdownBlock, ImageBlock, SectionBlock, ContextBlock, VideoBlock) round-trip fully.

Blocks that contain interactive elements (ActionsBlock, InputBlock, SectionBlock with an accessory, ContextBlock with image elements) raise NotImplementedError for now; these depend on Element.from_dict which is planned for a follow-up release.

Two new block types

Slack added these in 2024; they're now available:

from slackblocks import MarkdownBlock, VideoBlock

# Slack's GitHub-flavored markdown block (richer than SectionBlock mrkdwn).
MarkdownBlock(text="# Heading\n\n- item 1\n- item 2")

# Embed a video from a Slack-supported provider.
VideoBlock(
    alt_text="Demo",
    thumbnail_url="https://example.com/thumb.png",
    title="Getting Started",
    video_url="https://example.com/video.mp4",
)

Type-checking improvements

The 2.x series ships with substantially tighter type signatures. If you type-check your code with mypy, pyright, or Pyre, expect that:

Text.to_text("hi") is now correctly typed as Text (was previously Text | None). Code that did assert text is not None after to_text calls can drop the assertion.
Button(style="warning") is now flagged at type-check time — style is Literal["primary", "danger"] | ButtonStyle | None.
ColumnSettings(align="LEFT") is similarly flagged at type-check time.
ConversationFilter(include=["bogus"]) is flagged.

These constraints already existed at runtime; the difference is that mypy now agrees with the runtime behaviour.

Internal changes you might notice

The _resolve() method on every block, element, and composition object was refactored to use a shared slackblocks._core.resolve() walker. This is strictly internal — JSON output is byte-identical to 1.x — but if you have been subclassing internal classes you may notice the _resolve bodies are much shorter.

If you are extending slackblocks with custom classes:

If your custom class has a _resolve method that follows the existing pattern (manual if self.x is not None: out["x"] = self.x._resolve()), it continues to work in 2.x without modification.
If you want, you can switch to using the new slackblocks._core.resolve / omit_none helpers; doing so guarantees recursion into nested _resolve outputs and is much more concise.

Reporting issues

If you hit a real upgrade problem, please open an issue on GitHub — include your Python version, your slackblocks version (old and new), and a minimal repro.