Support Jinja2 template in prompt registry by B-Step62 · Pull Request #19772 · mlflow/mlflow

B-Step62 · 2026-01-06T13:08:25Z

🛠 DevTools 🛠

Install mlflow from this PR

# mlflow
pip install git+https://github.com/mlflow/mlflow.git@refs/pull/19772/merge
# mlflow-skinny
pip install git+https://github.com/mlflow/mlflow.git@refs/pull/19772/merge#subdirectory=libs/skinny

For Databricks, use the following command:

%sh curl -LsSf https://raw.githubusercontent.com/mlflow/mlflow/HEAD/dev/install-skinny.sh | sh -s pull/19772/merge

Related Issues/PRs

Resolve #18169. Continue of #18715,

What changes are proposed in this pull request?

Support Jinja2 systax and its resolution in prompt registry.

How is this PR tested?

Existing unit/integration tests
New unit/integration tests
Manual tests

Does this PR require documentation update?

Will be updated in a follow-up

Release Notes

Is this a user-facing change?

No. You can skip the rest of this section.
Yes. Give a description of this change to be included in the release notes for MLflow users.

Support rendering Jinja2 template syntax in MLflow Prompt Registry

What component(s), interfaces, languages, and integrations does this PR affect?

Components

How should the PR be classified in the release notes? Choose one:

rn/none - No description will be included. The PR will be mentioned only by the PR number in the "Small Bugfixes and Documentation Updates" section
rn/breaking-change - The PR will be mentioned in the "Breaking Changes" section
rn/feature - A new user-facing feature worth mentioning in the release notes
rn/bug-fix - A user-facing bug fix worth mentioning in the release notes
rn/documentation - A user-facing documentation change worth mentioning in the release notes

Should this PR be included in the next patch release?

Yes should be selected for bug fixes, documentation updates, and other small changes. No should be selected for new features and larger changes. If you're unsure about the release classification of this PR, leave this unchecked to let the maintainers decide.

What is a minor/patch release?

Minor release: a release that increments the second part of the version number (e.g., 1.2.0 -> 1.3.0).
Bug fixes, doc updates and new features usually go into minor releases.
Patch release: a release that increments the third part of the version number (e.g., 1.2.0 -> 1.2.1).
Bug fixes and doc updates usually go into patch releases.

Yes (this PR will be cherry-picked and included in the next patch release)
No (this PR will be included in the next minor release)

Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

…inja2 prompts Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

This commit adds official Jinja2 support to MLflow prompt templates, including auto-detection, sandboxed evaluation, and correct type tagging. All Jinja2-related tests under tests/genai/prompts/ now pass successfully. Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

…matting coverage Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

Signed-off-by: soyun11 <567654@o.cnu.ac.kr> Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

- Add environment variable for prompt cache TTL - Update registry_utils for prompt type detection - Add Jinja2 template support in MlflowClient.register_prompt() Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

- Fix Dummy mock to include required ModelVersion attributes - Update tests for Jinja2 detection and plain text fallback Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

…vior Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

…al MLflow behavior Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

github-actions · 2026-01-07T04:49:51Z

Please use /autoformat command instead of labels.

github-actions · 2026-01-07T04:54:59Z

Documentation preview for 26b1b6f is available at:

https://pr-19772--mlflow-docs-preview.netlify.app/docs/latest/

Changed Pages (1)

genai/prompt-registry (modified)

More info

Ignore this comment if this PR does not change the documentation.
The preview is updated when a new commit is pushed to this PR.
This comment was created by this workflow run.
The documentation was built by this workflow run.

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

B-Step62 · 2026-01-07T11:16:27Z

tests/tracking/test_client.py

    assert loaded_prompt.response_format is None


-def test_create_prompt_with_empty_chat_template_client():


note: It doesn't make sense to handle an empty list as a text prompt

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

mlflow/entities/model_registry/prompt_version.py

mlflow/prompt/constants.py

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

TomeHirata · 2026-01-14T00:32:05Z

mlflow/entities/model_registry/prompt_version.py

            Either a string (for text prompts) or a list of chat message dictionaries
            (for chat prompts) with 'role' and 'content' keys.
        """
-        if self.is_text_prompt:


What do we need this change for?

huh rebase collapse, thanks for the catch!

TomeHirata

LGTM

mlflow/entities/model_registry/prompt_version.py

Signed-off-by: Yuki Watanabe <31463517+B-Step62@users.noreply.github.com>

soyun11 and others added 13 commits November 16, 2025 18:50

Add Jinja2 prompt support: detection, formatting, tests, client logic

9055394

Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

Fix: ensure mlflow.prompt.type is stored and restored correctly for J…

a60c944

…inja2 prompts Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

test: refine Jinja2 prompt tests with improved classification and for…

3ff2333

…matting coverage Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

Restore .vscode/settings.json

1967539

Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

Fix: restore constants.py and add Jinja2 type

3776658

Signed-off-by: soyun11 <567654@o.cnu.ac.kr> Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

Fix: restore correct prompt constants and pass tests

f47530f

Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

feat(genai): add Jinja2 prompt support (core functionality)

f3233c6

- Add environment variable for prompt cache TTL - Update registry_utils for prompt type detection - Add Jinja2 template support in MlflowClient.register_prompt() Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

test(genai): update Jinja2 prompt tests and fix Dummy mock objects

1bc6e83

- Fix Dummy mock to include required ModelVersion attributes - Update tests for Jinja2 detection and plain text fallback Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

fix(prompts): refine Jinja2 formatting logic and restore version beha…

4409fb4

…vior Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

fix(prompts): revert chat formatting cosmetic changes and keep origin…

7716720

…al MLflow behavior Signed-off-by: soyun11 <567654@o.cnu.ac.kr>

Merge branch 'master' into feat/prompt-jinja2

00959a6

follow-up

89d89f5

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

github-actions bot added area/prompts MLflow Prompt Registry and Optimization rn/feature Mention under Features in Changelogs. labels Jan 6, 2026

pollish

847ee13

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

B-Step62 added the autoformat label Jan 7, 2026

github-actions bot removed the autoformat label Jan 7, 2026

fix test

2de01a0

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

B-Step62 requested a review from TomeHirata January 7, 2026 10:28

B-Step62 added 2 commits January 7, 2026 20:08

fix test

ce2d4f1

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

remove unrelated changes

b85349c

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

B-Step62 commented Jan 7, 2026

View reviewed changes

fix npe for maintainers check

120cb87

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

TomeHirata reviewed Jan 13, 2026

View reviewed changes

mlflow/entities/model_registry/prompt_version.py Outdated Show resolved Hide resolved

TomeHirata reviewed Jan 13, 2026

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mlflow/prompt/constants.py Outdated Show resolved Hide resolved

github-actions bot assigned TomeHirata Jan 13, 2026

comments

32b8be4

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

B-Step62 added 2 commits January 13, 2026 21:56

Merge branch 'master' into feat/prompt-jinja2

b0d564f

lint

bd158ef

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

B-Step62 force-pushed the feat/prompt-jinja2 branch from 03e4882 to bd158ef Compare January 13, 2026 12:59

clean up

ce0e8f6

Signed-off-by: B-Step62 <yuki.watanabe@databricks.com>

B-Step62 added the v3.9.0 label Jan 13, 2026

B-Step62 requested a review from TomeHirata January 14, 2026 00:09

TomeHirata reviewed Jan 14, 2026

View reviewed changes

TomeHirata approved these changes Jan 14, 2026

View reviewed changes

B-Step62 commented Jan 14, 2026

View reviewed changes

mlflow/entities/model_registry/prompt_version.py Outdated Show resolved Hide resolved

Apply suggestions from code review

26b1b6f

Signed-off-by: Yuki Watanabe <31463517+B-Step62@users.noreply.github.com>

B-Step62 enabled auto-merge January 14, 2026 01:12

B-Step62 disabled auto-merge January 14, 2026 08:43

B-Step62 merged commit cb9e30c into mlflow:master Jan 14, 2026
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Support Jinja2 template in prompt registry#19772

Support Jinja2 template in prompt registry#19772
B-Step62 merged 23 commits intomlflow:masterfrom
B-Step62:feat/prompt-jinja2

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		assert loaded_prompt.response_format is None


		def test_create_prompt_with_empty_chat_template_client():

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Install mlflow from this PR

Related Issues/PRs

What changes are proposed in this pull request?

How is this PR tested?

Does this PR require documentation update?

Release Notes

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