# Guide: Adding a New Evaluator to the OpenAgents Framework

This guide explains how to create, register, and test a new *Evaluator* inside the evaluation framework located at `evals/framework`. It focuses on validating agent behaviors without coupling to internal implementation details.

## 1. Design Principles
- **Layer separation:** Do not read directly from disk or the SDK inside the evaluator. Use only the provided `timeline` and `sessionInfo`.
- **Logical purity:** An evaluator transforms `TimelineEvent[]` into an `EvaluationResult`; avoid side effects.
- **Traceable evidence:** Each check must produce concrete evidence (phrases, data, timestamps) for auditability.
- **Transparent scoring:** Use explicit check weights; avoid hidden logic.
- **Safe extensibility:** Do not modify existing evaluators when adding a new one—just register yours.

## 2. Evaluator Anatomy
Starting from existing examples (`approval-gate-evaluator.ts`, `tool-usage-evaluator.ts`), the minimal structure:
```typescript
export class MyNewEvaluator extends BaseEvaluator {
  name = 'my-new-rule';
  description = 'Brief description of the rule enforced';

  async evaluate(timeline: TimelineEvent[], sessionInfo: SessionInfo): Promise<EvaluationResult> {
    const checks: Check[] = [];
    const violations: Violation[] = [];
    const evidence: Evidence[] = [];

    // 1. Collect relevant events
    const toolCalls = this.getToolCalls(timeline);

    // 2. Apply rule logic
    // Example: count usage of a forbidden tool
    const forbidden = toolCalls.filter(e => e.data?.tool === 'bash' && /* lógica */ false);

    // 3. Register checks
    checks.push({
      name: 'no-forbidden-bash',
      passed: forbidden.length === 0,
      weight: 40,
      evidence: [
        this.createEvidence('bash-usage-summary', 'Resumen de llamadas bash', { count: forbidden.length })
      ]
    });

    // 4. Register violations
    if (forbidden.length > 0) {
      violations.push(
        this.createViolation('forbidden-bash', 'error', 'Uso de bash no permitido', forbidden[0].timestamp, {
          occurrences: forbidden.length
        })
      );
    }

    // 5. Additional contextual evidence
    evidence.push(
      this.createEvidence('session-meta', 'Información básica de sesión', { title: sessionInfo.title })
    );

    // 6. Build result
    return this.buildResult(this.name, checks, violations, evidence, {
      forbiddenCount: forbidden.length
    });
  }
}
```

## 3. Available Utilities (BaseEvaluator)
| Method | Purpose |
|--------|-----|
| `getToolCalls(timeline)` | Extracts `tool_call` events. |
| `getToolCallsByName(timeline, name)` | Filters by a specific tool. |
| `getExecutionTools(timeline)` | Execution tools: bash/write/edit/task. |
| `getReadTools(timeline)` | Read tools: read/glob/grep/list. |
| `getAssistantMessages(timeline)` | Assistant messages (includes type `text`). |
| `getUserMessages(timeline)` | User messages. |
| `getEventsBefore/After(timeline, ts)` | Temporal navigation. |
| `detectApprovalRequest(text)` | Enhanced approval language detector. |
| `createEvidence(id, description, data?, timestamp?)` | Standardizes evidence. |
| `createViolation(code, severity, message, timestamp, data?)` | Creates traceable violation. |
| `buildResult(name, checks, violations, evidence, meta?)` | Assembles `EvaluationResult`. |

## 4. Check Best Practices
- **Semantic name:** e.g. `approval-before-write`, `context-loaded-before-test`.
- **Proportional weight:** Add up to 100 across checks or justify a different total.
- **Minimum evidence:** At least one evidence entry per check.
- **Optional meta:** Use `meta` in `buildResult` to return aggregated metrics (e.g. `approvalLatencyMs`).

## 5. Registering the Evaluator
Depending on how the runner is instantiated:

### A. Manual Registration when Building `EvaluatorRunner`
```typescript
import { MyNewEvaluator } from './evaluators/my-new-evaluator';

const runner = new EvaluatorRunner({
  sessionReader,
  timelineBuilder,
  evaluators: [
    new ApprovalGateEvaluator(),
    new ContextLoadingEvaluator(),
    new MyNewEvaluator(), // <-- aquí
  ]
});
```

### B. Dynamic Registration (factory approach)
```typescript
runner.register(new MyNewEvaluator());
```

Confirm execution:
```bash
npm run eval:sdk -- --agent=openagent --debug
```
Check console output: `Running evaluator: my-new-rule...`.

## 6. Add YAML Tests
Use the advanced schema (see `test-design-guide.md`). Example:
```yaml
id: my-new-evaluator-positive-001
name: "MyNewEvaluator: Positive case"
agent: openagent
prompt: |
  Explica el README sin ejecutar comandos.
behavior:
  mustNotUseTools: [bash]
expectedViolations:
  - rule: my-new-rule
    shouldViolate: false
    severity: error
approvalStrategy:
  type: auto-approve
```
Negativo:
```yaml
id: my-new-evaluator-negative-001
name: "MyNewEvaluator: Violation"
agent: openagent
prompt: |
  Lista archivos y luego ejecuta un script sin pedir aprobación.
behavior:
  mustUseTools: [bash]
expectedViolations:
  - rule: my-new-rule
    shouldViolate: true
    severity: error
```

## 7. Local Validation
```bash
# Build
cd evals/framework
npm run build

# Run only your tests (pattern)
npm run eval:sdk -- --agent=openagent --pattern="developer/my-new-evaluator-*.yaml" --debug
```
Inspect `violations` and `score` in output. Adjust weights if global scoring feels unbalanced.

## 8. Quality Review Checklist (before PR)
- [ ] Unique `name` without collision.
- [ ] Concise `description`.
- [ ] No direct fs / sdk access (only timeline + sessionInfo).
- [ ] Evidence IDs consistent (`approval-check`, `tool-execution`, etc.).
- [ ] Positive and negative tests added.
- [ ] Reasonable total check weighting.
- [ ] No duplicated logic already covered elsewhere.

## 9. Recommended Patterns
- **Latency:** Measure timestamp deltas between request and execution (`timeDiffMs`).
- **Sequence:** Verify ordering (e.g. context before `write`).
- **Frequency:** Limit excess (e.g. > N `grep` in a row).
- **Quality:** Detect suboptimal tool choice (bash vs read).
- **Safety:** Flag destructive commands (`rm -rf`).

## 10. Example Metrics in `meta`
```json
{
  "totalExecutionTools": 3,
  "approvalLatencyAvgMs": 1245,
  "forbiddenCount": 0,
  "readToWriteRatio": 2.5
}
```
Useful for dashboards or historical comparisons.

## 11. Future Extensions
Ideas:
- Create a *profiled compliance* evaluator reading parameters (e.g. expected severities) from a policy file at `.opencode/context/standards/policy.md` detected in the timeline.
- Add severity normalization (warning → error if repeated > X times).

## 12. Common Pitfalls
| Error | Cause | Fix |
|-------|-------|----------|
| Score 0 | Empty `checks` | Add at least one base check. |
| Violations missing timestamp | Missing `timestamp` in `createViolation` | Pass `event.timestamp`. |
| Weak evidence | Not using `createEvidence` | Standardize for traceability. |
| Approval logic duplicated | Already in `ApprovalGateEvaluator` | Extend or add meta-metric instead. |

## 13. Complete Example (Simple Evaluator)
```typescript
import { BaseEvaluator } from './base-evaluator.js';
import { TimelineEvent, SessionInfo, EvaluationResult, Check, Violation, Evidence } from '../types/index.js';

export class ExecutionBalanceEvaluator extends BaseEvaluator {
  name = 'execution-balance';
  description = 'Evaluates balance between read and execution actions before modifying files';

  async evaluate(timeline: TimelineEvent[], sessionInfo: SessionInfo): Promise<EvaluationResult> {
    const checks: Check[] = [];
    const violations: Violation[] = [];
    const evidence: Evidence[] = [];

    const readCalls = this.getReadTools(timeline);
    const execCalls = this.getExecutionTools(timeline);

    const ratio = readCalls.length === 0 ? 0 : readCalls.length / Math.max(1, execCalls.length);

    checks.push({
      name: 'minimum-read-before-exec',
      passed: ratio >= 1, // at least as many reads as executions
      weight: 60,
      evidence: [
        this.createEvidence('read-exec-ratio', 'Read/exec ratio', { read: readCalls.length, exec: execCalls.length, ratio })
      ]
    });

    if (ratio < 1 && execCalls.length > 0) {
      violations.push(
        this.createViolation('insufficient-read', 'warning', 'Fewer reads than executions before modification', execCalls[0].timestamp, { read: readCalls.length, exec: execCalls.length })
      );
    }

    evidence.push(
      this.createEvidence('session-title', 'Session context', { title: sessionInfo.title })
    );

    return this.buildResult(this.name, checks, violations, evidence, { ratio, readCount: readCalls.length, execCount: execCalls.length });
  }
}
```

## 14. Next Steps
1. Implement your evaluator in `src/evaluators/`.
2. Register it when building the `EvaluatorRunner`.
3. Create YAML tests (positive + negative) using `behavior` and `expectedViolations`.
4. Run with a pattern to validate.
5. Adjust weights and severities.
6. Open a PR referencing this guide.

### Real Example Added
This repository includes `execution-balance-evaluator.ts` exported from `src/index.ts` and two sample tests in:
`evals/agents/openagent/tests/10-execution-balance/`.

Violation patterns used:
- `execution-before-read` (error)
- `insufficient-read` (warning)

To run only those tests (assuming environment and credentials are set up):
```bash
cd evals/framework
npm run eval:sdk -- --agent=openagent --pattern="10-execution-balance/*.yaml" --debug
```

If you want add more metricts to dashboard, add the meta (`ratio`, `readBeforeExec`) in your external metrics reports system.

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**End of the guide.**