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

Set `source:` to a TiDB-kind source name.

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

tidb-sql's ValidateSource requires the bound source to implement compatibleSource (TiDB-compatible). Any other source type fails the interface assertion, producing this error and blocking invocation with a mismatched engine.

Source

Thrown at internal/tools/tidb/tidbsql/tidbsql.go:130

	res, err := source.RunSQL(ctx, newStatement, sliceParams)
	if err != nil {
		return nil, util.ProcessGeneralError(err)
	}
	return res, nil
}

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

Set `source:` to a TiDB-kind source name.
Add the missing TiDB source declaration.
Run a config lint that checks tool kind vs source kind pairs.

Example fix

# before
source: spanner-prod
# after
source: tidb-prod

Defensive patterns

Strategy: type-guard

Validate before calling

# check each tidb-sql tool's source kind is TiDB
yq '.tools[] | select(.kind == "tidb-sql") | .source' tools.yaml

Type guard

func isTiDBSource(s sources.Source) bool {
    _, ok := s.(tidbsql.CompatibleSource)
    return ok
}

Try / catch

if err := tool.ValidateSource(src); err != nil {
    log.Fatalf("bad source binding for tidb-sql: %v", err)
}

Prevention

Pair tool definitions with their sources in per-engine config files.
Run startup validation before serving traffic.
Keep source names unique across engines to avoid wrong bindings.

When it happens

Trigger: `tidb-sql` tool bound to a non-TiDB source via `source:`; direct Go call passing an incompatible source.

Common situations: Multi-database configs where tool/source names were swapped; refactors that renamed sources without updating tool bindings.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/10bf1cd9dac15a09. Report an issue: GitHub.