What causes "Cannot use FormatSchema of type {} for format {}" in FasterXML/jackson-databind?

Use the format-specific mapper: new CsvMapper().writer(schema).writeValue(...).

FasterXML/jackson-databind · error · IllegalArgumentException

Cannot use FormatSchema of type

Error message

Cannot use FormatSchema of type {} for format {}

What it means

Thrown by ObjectWriter._verifySchemaType() when a FormatSchema is set on the writer but the underlying generator factory cannot use it. Each format has its own schema type; passing a schema from a different format is a type mismatch. The check uses the generator factory's canUseSchema() method.

Solutions

Use the format-specific mapper: new CsvMapper().writer(schema).writeValue(...).
Verify the writer's factory getFormatName() matches the schema's expected format before calling with(schema).
Construct the writer from the same format-specific mapper that produced the schema.

Example fix

// before
ObjectWriter w = jsonMapper.writer(csvSchema); // throws
// after
ObjectWriter w = csvMapper.writer(csvSchema);

Defensive patterns

Strategy: validation

Validate before calling

// Check schema compatibility before setting
if (schema != null && !writer._generatorFactory.canUseSchema(schema)) {
    throw new IllegalArgumentException("Schema incompatible with writer format");
}

Type guard

boolean schemaMatchesGenerator(JsonFactory factory, FormatSchema schema) {
    return schema == null || factory.canUseSchema(schema);
}

Prevention

Use the format-specific mapper that matches your schema.
Never cross schema types between formats.
Construct writer and schema from the same format-specific mapper.

When it happens

Trigger: Calling writer.with(schema) where schema is, e.g., a CsvSchema but the writer is backed by a JsonFactory. Same mismatch issue as the reader side but on the serialization path.

Common situations: Using a JSON ObjectMapper to write CSV or YAML with a format-specific schema. Copy-pasting schema code between format contexts. Module configuration that replaces the default factory.

Related errors

AI-assisted analysis of FasterXML/jackson-databind@87876ca5c0 (2026-08-11). Data as JSON: /api/errors/295d4a514a9cf0b2. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/tools/jackson/databind/ObjectWriter.java:1279

    /**
     * Overridable helper method used for constructing
     * {@link SerializationContext} to use for serialization.
     */
    protected final SerializationContextExt _serializationContext() {
        return _serializationContexts.createContext(_config, _generatorSettings);
    }

    /*
    /**********************************************************************
    /* Internal methods
    /**********************************************************************
     */

    protected void _verifySchemaType(FormatSchema schema)
    {
        if (schema != null) {
            if (!_generatorFactory.canUseSchema(schema)) {
                    throw new IllegalArgumentException("Cannot use FormatSchema of type "+schema.getClass().getName()
                            +" for format "+_generatorFactory.getFormatName());
            }
        }
    }

    /**
     * Helper method that applies configured {@link GeneratorInitializer},
     * if any, to the given generator and returns it.
     *
     * @since 3.2
     */
    protected JsonGenerator _initializeGenerator(JsonGenerator gen) {
        GeneratorInitializer init = _config.getGeneratorInitializer();
        if (init != null) {
            init.initialize(_config, gen);
        }
        return gen;
    }

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