How to validate JSON with a schema in Python?
Jul 09, 2025 am 12:54 AMA common way to verify that JSON data complies with a specific structure is to use the jsonschema library. 1. Install the library: pip install jsonschema; 2. Define the schema to describe the expected structure; 3. Use the validate function to verify the data. If it does not match, an exception will be thrown. Common considerations include field type matching, required fields exist, correct description of nested structures, and default values ??will not be automatically filled. Alternatives are Pydantic and fastjsonschema, which are suitable for complex models or scenarios with high performance requirements. Pay attention to the consistency between schema writing and data during operation.
Verifying that JSON data complies with a specific structure is very common in development, especially when handling API requests, configuration files, or data import and export. Python provides some simple and practical ways to implement this function.

Verification using jsonschema library
The most common way is to use jsonschema
, a third-party library. It implements the JSON Schema standard and is very intuitive to use.
First you need to install it:

pip install jsonschema
Then you can define a schema and use it to verify your JSON data. For example:
from jsonschema import validate schema = { "type": "object", "properties": { "name": {"type": "string"}, "age": {"type": "number"} }, "required": ["name"] } data = {"name": "Alice", "age": 30} validate(instance=data, schema=schema)
If the data does not match the schema, an exception will be thrown. This method is suitable for most scenarios where structural verification is required.

Common Errors and Precautions
In actual use, some details are easily overlooked:
- Field type mismatch : For example, if you expect it to be a string but a number is passed, the verification will fail.
- Required fields are missing : As long as
"required"
is written in the schema, these fields must appear in the data. - The nested structure is not written correctly : especially when objects or arrays are nested, the schema must accurately describe the structure of each layer.
- Ignore the default value : JSON Schema will not automatically fill in the default value. If you need such behavior, you have to deal with it yourself.
When encountering problems, you can print exception information, or use jsonschema.exceptions.validate()
to get more detailed error content.
Other alternatives
In addition to jsonschema
, there are some other methods or tools that can also complete similar tasks:
- Using Pydantic (for more complex models)
- Using fastjsonschema (faster pure Python implementation)
- Manually write logical judgment structure (not recommended, high maintenance cost)
For most projects, jsonschema
is useful enough. If you have performance requirements, you can consider fastjsonschema
; and if you are already using Pydantic for data model management, it is also a good choice.
Basically that's it. The operation is not complicated, but pay attention to the consistency of the schema writing method and data.
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