What causes "invalid source for %q tool: source %q is not a compatible type" in googleapis/mcp-toolbox?

Point the tool's `source` at a `kind: singlestore` source.

invalid source for %q tool: source %q is not a compatible ty

Error message

invalid source for %q tool: source %q is not a compatible type

What it means

The singlestore-sql tool throws this in ValidateSource when its configured source fails the `compatibleSource` type assertion — the source is not a SingleStore source exposing the expected database pool. This is a startup-time guard: Toolbox validates every tool/source pairing while loading tools.yaml so incompatible combinations are rejected before serving requests.

Source

Thrown at internal/tools/singlestore/singlestoresql/singlestoresql.go:156

}

// EmbedParams overrides BaseTool to apply the pgvector formatter.
func (t Tool) EmbedParams(ctx context.Context, paramValues parameters.ParamValues, pMgr tools.PrimitiveManagerI) (parameters.ParamValues, error) {
	return parameters.EmbedParams(ctx, t.StaticParameters, paramValues, pMgr, embeddingmodels.FormatVectorForPgvector)
}

func (t Tool) GetSourceName() string {
	return t.Cfg.Source
}

func (t Tool) ToConfig() tools.ToolConfig {
	return t.Cfg
}

func (t Tool) ValidateSource(source sources.Source) error {
	_, ok := source.(compatibleSource)
	if !ok {
		return fmt.Errorf("invalid source for %q tool: source %q is not a compatible type", t.Cfg.Type, t.Cfg.Source)
	}
	return nil
}

View on GitHub (pinned to 8cc6e09de2)

Solutions

Point the tool's `source` at a `kind: singlestore` source.
Add a properly configured singlestore source if missing, then reference it.
Validate the full tools.yaml by starting Toolbox locally and resolving all ValidateSource errors before deploying.

Example fix

# before
tools:
  query-tool:
    kind: singlestore-sql
    source: pg-src
# after
tools:
  query-tool:
    kind: singlestore-sql
    source: singlestore-src

Defensive patterns

Strategy: validation

Validate before calling

sources:
  singlestore-src:
    kind: singlestore
tools:
  query-tool:
    kind: singlestore-sql
    source: singlestore-src

Type guard

func isSingleStoreSource(s sources.Source) bool {
    _, ok := s.(singlestore.Source)
    return ok
}

Prevention

Cross-check every singlestore-sql tool's source against the sources section after merges.
Avoid generic source names like `db` that invite cross-engine misbinding.
Validate configs by starting Toolbox locally; the error names the exact tool and source.

When it happens

Trigger: A `singlestore-sql` tool whose `source:` names a source of another kind (e.g. postgres, mssql), so `source.(compatibleSource)` returns false in singlestoresql.go and the formatted error is returned.

Common situations: Mixed-database configs where similar tool names (postgres-sql vs singlestore-sql) get swapped sources; copy-paste from another integration's docs; config merge tools rewriting source keys.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/97620ca8a99c6ef2. Report an issue: GitHub.