JuliusBrussee/caveman · error

filter must be a boolean

Error message

filter ${key} must be a boolean

What it means

Validation error from validateTraceFilters in the agent MCP server: a filter key declared as boolean was supplied with a non-boolean value. The MCP client sent JSON whose type does not match the filter contract for that key.

Solutions

1. Pass real booleans: has_error: true
2. Convert strings with value === 'true' / 'false' before calling
3. Omit the key when the flag is unknown rather than passing null

Example fix

// before
searchTraces({ filters: { has_error: 'true' } });
// after
searchTraces({ filters: { has_error: hasError === 'true' } });

function assertBooleanFilters(filters) {
  for (const key of ['has_error', 'compressed']) {
    const v = filters?.[key];
    if (v !== undefined && typeof v !== 'boolean') {
      throw new Error(`filter ${key} must be a boolean`);
    }
  }
}

function isBoolean(v) {
  return typeof v === 'boolean';
}

try {
  await searchTraces({ filters });
} catch (error) {
  const m = error.message.match(/^filter (\w+) must be a boolean/);
  if (m) {
    if (filters[m[1]] === 'true') filters[m[1]] = true;
    else if (filters[m[1]] === 'false') filters[m[1]] = false;
    else delete filters[m[1]];
  }
}

When it happens

Trigger: Passing { has_error: 'true' }, { compressed: 1 }, { has_error: null }, or a query-string-derived "false" string.

Common situations: URL query params arriving as strings; UIs emitting 0/1; serialization layers coercing booleans; LLM-generated tool args using the string "true".

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• filter monitor must be an object
• filters must be an object
• filter must be a finite number
• filter must be a non-empty array of non-empty strings
• filter status_class values must be 2xx, 4xx, or 5xx

AI-assisted analysis of JuliusBrussee/caveman@3ee70a1026 (2026-09-20). Data as JSON: /api/errors/059e1192b251cc1e. Report an issue: GitHub.

Appendix: source

Thrown at packages/cli/src/agent-mcp.ts:486

  for (const key of stringListKeys) {
    const value = filters[key];
    if (value === undefined) continue;
    if (!Array.isArray(value) || value.length === 0 || value.some((entry) => typeof entry !== "string" || entry.trim() === "")) {
      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(", ")}`);
  }

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