microsoft/aspire · error · JsonException

Cannot convert to boolean for key

Error message

Cannot convert {reader.TokenType} to boolean for key '{key}'

What it means

Inside the dictionary converter, each property value must be a JSON true/false literal or a 'true'/'false' string; any other token (number, null, object, array) throws JsonException naming the token and key. The converter deliberately only flexes for string booleans.

Solutions

1. Replace the numeric/null value with true or false (or the strings "true"/"false") for the key named in the message.
2. If the value legitimately needs to be non-boolean, move it to a different config key, not the boolean dictionary.
3. If 1/0 support is desired, extend the switch's ParseBooleanString path to accept numeric tokens.

Example fix

// before
"featureFlags": { "MyFeature": 1 }
// after
"featureFlags": { "MyFeature": true }

using var doc = JsonDocument.Parse(json);
foreach (var p in doc.RootElement.GetProperty("featureFlags").EnumerateObject())
{
    if (p.Value.ValueKind is not (JsonValueKind.True or JsonValueKind.False or JsonValueKind.String))
        throw new FormatException($"Feature flag '{p.Name}' must be true/false or \"true\"/\"false\".");
}

try
{
    var config = JsonSerializer.Deserialize<MyConfig>(json, options);
}
catch (JsonException ex) when (ex.Message.Contains("Cannot convert") && ex.Message.Contains("to boolean"))
{
    logger.LogError(ex, "Config dictionary contains a value that is not a boolean.");
}

When it happens

Trigger: A value in a Dictionary<string,bool> config object that is a number (1/0), null, nested object, or array, e.g. "featureFlags": { "MyFeature": 1 }.

Common situations: Users familiar with other config systems writing 1/0 or yes/no; values interpolated from env vars carrying raw numbers; schema assumptions from other tooling.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• Cannot convert string
• ' ' must be a JSON string.
• ' ' must be a JSON string.
• ' ' must contain a JSON object.
• Expected StartObject, got

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/3092c5673d08dfad. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Cli/Configuration/FlexibleBooleanDictionaryConverter.cs:51

            {
                return dictionary;
            }

            if (reader.TokenType != JsonTokenType.PropertyName)
            {
                throw new JsonException($"Expected PropertyName, got {reader.TokenType}");
            }

            var key = reader.GetString() ?? throw new JsonException("Property name cannot be null");

            reader.Read();

            bool value = reader.TokenType switch
            {
                JsonTokenType.True => true,
                JsonTokenType.False => false,
                JsonTokenType.String => ParseBooleanString(reader.GetString(), key),
                _ => throw new JsonException($"Cannot convert {reader.TokenType} to boolean for key '{key}'")
            };

            dictionary[key] = value;
        }

        throw new JsonException("Unexpected end of JSON");
    }

    public override void Write(Utf8JsonWriter writer, Dictionary<string, bool> value, JsonSerializerOptions options)
    {
        writer.WriteStartObject();

        foreach (var kvp in value)
        {
            writer.WriteBoolean(kvp.Key, kvp.Value);
        }

        writer.WriteEndObject();

View on GitHub (pinned to 25830f84bd)