JuliusBrussee/caveman · warning

filter monitor must be an object

Error message

filter monitor must be an object

What it means

The nested `monitor` filter must be a plain JSON object (with only id and verdict keys) when present. Passing null, an array, a string, or a number throws this error before the key-level monitor checks run.

Source

Thrown at packages/cli/src/agent-mcp.ts:490

      throw new Error(`filter ${key} must be a non-empty array of non-empty strings`);
    }
    if (key === "status_class" && value.some((entry) => !["2xx", "4xx", "5xx"].includes(entry as string))) {
      throw new Error("filter status_class values must be 2xx, 4xx, or 5xx");
    }
  }
  for (const key of ["min_cost_usd", "max_cost_usd", "min_total_tokens", "max_total_tokens", "min_latency_ms", "max_latency_ms"]) {
    const value = filters[key];
    if (value !== undefined && (typeof value !== "number" || !Number.isFinite(value))) {
      throw new Error(`filter ${key} must be a finite number`);
    }
  }
  for (const key of ["has_error", "compressed"]) {
    const value = filters[key];
    if (value !== undefined && typeof value !== "boolean") throw new Error(`filter ${key} must be a boolean`);
  }
  const monitor = filters.monitor;
  if (monitor !== undefined) {
    if (!monitor || typeof monitor !== "object" || Array.isArray(monitor)) throw new Error("filter monitor must be an object");
    const monitorUnknown = Object.keys(monitor).filter((key) => key !== "id" && key !== "verdict");
    if (monitorUnknown.length > 0) throw new Error(`filter monitor has unknown key(s): ${monitorUnknown.sort().join(", ")}`);
    if (typeof monitor.id !== "string" || monitor.id.trim() === "") throw new Error("filter monitor.id is required");
    if (typeof monitor.verdict !== "string" || !["pass", "fail", "error"].includes(monitor.verdict)) {
      throw new Error("filter monitor.verdict must be pass, fail, or error");
    }
  }
}

function optionalEnum(args: JSONObject, key: string, values: string[]): void {
  const value = args[key];
  if (value !== undefined && (typeof value !== "string" || !values.includes(value))) {
    throw new Error(`${key} must be one of ${values.join(", ")}`);
  }
}

function validateTraceSearch(args: JSONObject): void {
  validateTraceFilters(args);

View on GitHub (pinned to 27d5a3981a)

Solutions

1. Pass monitor as an object: {"monitor": {"id": "mon_123", "verdict": "pass"}}.
2. Omit the monitor key entirely when not filtering by monitor.
3. Omit verdict if you only need id — only id is required inside monitor.

Example fix

// before
{ filters: { monitor: "mon_123" } }

// after
{ filters: { monitor: { id: "mon_123" } } }

if (filters.monitor !== undefined && (typeof filters.monitor !== "object" || filters.monitor === null || Array.isArray(filters.monitor))) {
  throw new Error("monitor must be an object");
}

function isMonitorFilter(v: unknown): v is { id?: string; verdict?: string } {
  return typeof v === "object" && v !== null && !Array.isArray(v);
}

When it happens

Trigger: filters.monitor = "mon_123"; filters.monitor = ["mon_123"]; filters.monitor = null sent instead of omitting the key.

Common situations: Shorthand single-id forms; clients defaulting optional objects to null; double-encoded JSON strings.

Related errors

• filter monitor has unknown key(s): ${monitorUnknown.sort().j
• filter monitor.verdict must be pass, fail, or error
• filters must be an object
• unknown trace filter(s): ${unknown.sort().join(", ")}
• filter ${key} must be a non-empty array of non-empty strings

AI-assisted analysis of JuliusBrussee/caveman@27d5a3981a (2026-08-15). Data as JSON: /api/errors/4498c2c146a5a589. Report an issue: GitHub.