hasura/graphql-engine · error · Error

unable to serialize to json: {0}

Error message

unable to serialize to json: {0}

What it means

Serializing the introspection response to JSON failed (serde_json::Error). The introspection result could not be written to JSON, usually because a value in the schema response is not JSON-representable or contains an invalid value (e.g. invalid UTF-8 string in a name/description).

Source

Thrown at v3/crates/graphql/lang-graphql/src/generate_graphql_schema.rs:23

use json_ext;
use std::collections::BTreeMap;
use std::sync::OnceLock;
use tracing_util::SpanVisibility;
use tracing_util::{ErrorVisibility, TraceableError};

#[derive(Debug, thiserror::Error)]
pub enum Error {
    #[error("unable to parse introspection query: {0}")]
    ParseIntrospectionQuery(String),
    #[error("unable to normalize introspection query: {0}")]
    NormalizeIntrospectionQuery(String),
    #[error("unable to find field call")]
    FieldCallNotFound,
    #[error("Only __schema field is expected but found: {name:}")]
    OnlySchemaFieldExpected { name: String },
    #[error("introspection query failed: {0}")]
    IntrospactionQueryError(#[from] crate::introspection::Error),
    #[error("unable to serialize to json: {0}")]
    SerializeJson(#[from] serde_json::Error),
}
impl TraceableError for Error {
    fn visibility(&self) -> ErrorVisibility {
        ErrorVisibility::User
    }
}

/// Generate GraphQL schema for a given namespace
pub fn build_namespace_schema<
    S: crate::schema::SchemaContext,
    NSGet: crate::schema::NamespacedGetter<S>,
>(
    namespaced_getter: &NSGet,
    schema: &crate::schema::Schema<S>,
) -> Result<serde_json::Value, Error> {
    let tracer = tracing_util::global_tracer();
    tracer.in_span(

View on GitHub (pinned to 724551b9ae)

Solutions

1. Check the inner serde_json error to find the offending value
2. Fix invalid UTF-8 or unserializable content in schema names/descriptions/metadata
3. Regenerate metadata from clean sources

// Validate metadata strings are valid UTF-8 before applying
if (!Buffer.from(name, 'utf8').toString('utf8') === name) throw new Error('bad encoding');

const isSafeUtf8 = (s) => { try { new TextEncoder().encode(s); return s === new TextDecoder().decode(new TextEncoder().encode(s)); } catch { return false; } };

// Catch, read the serde_json inner error to locate the unserializable value

When it happens

Trigger: Executing introspection on a schema whose names or descriptions contain invalid UTF-8 or other non-serializable content; map keys colliding in an unexpected way in the response.

Common situations: Metadata descriptions sourced from files with bad encodings; schema strings built from raw byte data.

Related errors

• unable to fetch introspection schema: %w
• error in fetching introspection schema: %w
• %s: %d %s
• %s: decoding graphql response errors: %w
• %s: %w

AI-assisted analysis of hasura/graphql-engine@724551b9ae (2026-08-28). Data as JSON: /api/errors/e6475a90653d2536. Report an issue: GitHub.