Pydantic JSON schema uses allOf when adding

The Fix

pip install pydantic==1.10.18

Based on closed pydantic/pydantic issue #10031 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -265,11 +265,6 @@ def modify_model_json_schema(
     json_schema = handler(schema_or_field)
     original_schema = handler.resolve_ref_schema(json_schema)
-    # Preserve the fact that definitions schemas should never have sibling keys:
-    if '$ref' in original_schema:
-        ref = original_schema['$ref']

repro.py

from pydantic import BaseModel, ConfigDict, Field

class Test(BaseModel):
    val: str = "test"
    
class Foo(BaseModel):
    bar: Test = Field(description="test")
    quz: Test

Foo.model_json_schema()

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install pydantic==1.10.18\nWhen NOT to use: This fix should not be applied if the behavior of allOf is required for specific schema validation.\n\n

Why This Fix Works in Production

Trigger: JSON schema uses allOf when adding Field(description="")
Mechanism: The JSON schema incorrectly adds an allOf wrapper when a description is provided for a Field
Why the fix works: Removes the unnecessary allOf JSON schema workarounds, allowing sibling keys alongside $ref keys. (first fixed release: 1.10.18).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Shows up under Python 3.11 in real deployments (not just unit tests).
The JSON schema incorrectly adds an allOf wrapper when a description is provided for a Field
Production symptom (often without a traceback): JSON schema uses allOf when adding Field(description="")

Proof / Evidence

GitHub issue: #10031
Fix PR: https://github.com/pydantic/pydantic/pull/10029
First fixed release: 1.10.18
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.64

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“Hi @kwint, Thanks for reporting this. I think this should be fixed by https://github.com/pydantic/pydantic/pull/10029 :)”

@sydney-runkle · 2024-08-02 · confirmation · source

Failure Signature (Search String)

JSON schema uses allOf when adding Field(description="")
When adding a description to a Field the schema adds an extra layer with an `allOf` array.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
JSON schema uses allOf when adding Field(description="")
When adding a description to a Field the schema adds an extra layer with an `allOf` array.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
JSON schema uses allOf when adding Field(description="")
When adding a description to a Field the schema adds an extra layer with an `allOf` array.

Minimal Reproduction

repro.py

from pydantic import BaseModel, ConfigDict, Field

class Test(BaseModel):
    val: str = "test"
    
class Foo(BaseModel):
    bar: Test = Field(description="test")
    quz: Test

Foo.model_json_schema()

Environment

Python: 3.11
Pydantic: 2

What Broke

The generated JSON schema does not match the expected format, causing integration issues.

Why It Broke

The JSON schema incorrectly adds an allOf wrapper when a description is provided for a Field

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install pydantic==1.10.18

When NOT to use: This fix should not be applied if the behavior of allOf is required for specific schema validation.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/pydantic/pydantic/pull/10029

First fixed release: 1.10.18

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix should not be applied if the behavior of allOf is required for specific schema validation.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.

Version Compatibility Table

Version	Status
1.10.18	Fixed

Related Issues

No related fixes found.

Cluster: pydantic:configuration-error Pydantic hub Pydantic best practices All hubs All clusters

Related clusters: Data consistency OpenAPI schema Serialization

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Pydantic JSON schema uses allOf when adding Field(description="") (Fix)