---
title: "Concepts"
description: "Core concepts behind PandaProbe's evaluation framework: runs, metrics, scores, signals, and monitors."
icon: "shapes"
---

This page explains the core building blocks of PandaProbe evaluation and how they fit together.

At a high level:

1. An **eval run** selects traces or sessions to evaluate.
2. One or more **metrics** run against each selected item.
3. Each metric produces a **score** with a value, reason, and metadata.
4. Optional **monitors** repeat eval runs on a schedule.

## Eval runs

An **eval run** is a batch job that applies one or more metrics to a target set of traces or sessions.

Every eval run has:

- A **target type**: `TRACE` or `SESSION`
- A list of **metrics** to run
- Optional **filters** that choose which traces or sessions are included
- Optional **sampling** to evaluate a fraction of matching data

When you create an eval run, PandaProbe:

1. Resolves the target data (traces or sessions) based on your filters
2. Optionally samples a fraction of the matches
3. Dispatches the work to a background worker
4. Returns immediately with status `PENDING`

The API responds with `202 Accepted`; the metric computation happens asynchronously. You can poll the run status or review results in the dashboard.

An eval run has a lifecycle:

| Status | Meaning |
|---|---|
| `PENDING` | Created, waiting for a worker to pick it up |
| `RUNNING` | Worker is actively evaluating traces/sessions |
| `COMPLETED` | All metrics finished (some individual scores may have failed) |
| `FAILED` | The run itself encountered a fatal error |

Each run tracks progress fields such as `evaluated_count` and `failed_count` so you can monitor completion and failures.

## Metrics

A **metric** is a reusable evaluation function that scores one trace or one session. PandaProbe ships with 11 built-in metrics across two categories.

### Trace-level metrics

Trace metrics evaluate an individual trace: the spans, inputs, outputs, tool calls, model calls, and metadata captured during one agent operation.

Most trace metrics use an **LLM-as-judge** approach. The metric extracts relevant information from the trace, asks an LLM to judge a specific quality dimension, and parses the structured response into a score.

Some trace metrics use embedding or similarity analysis instead:

- **Coherence** measures input-output alignment using embeddings.
- **Loop detection** compares traces in the same session to detect repeated behavior.

<Note>
  Most trace metrics can run on a single trace by itself. `loop_detection` needs session context because it compares the current trace with previous traces in the same session.
</Note>

### Session-level metrics

Session metrics evaluate an entire agent lifecycle. Instead of judging one trace, they aggregate signals from the traces in a session to answer broader questions about agent reliability and consistency.

Session-level aggregation is deterministic. PandaProbe first computes trace-level signals, then combines them mathematically into session scores.

The two session metrics, `agent_reliability` and `agent_consistency`, use four trace-level signals:

| Signal | Weight | Source metric |
|---|---|---|
| `confidence` | 1.0 | `confidence` metric |
| `loop_detection` | 1.0 | `loop_detection` metric |
| `tool_correctness` | 0.8 | `tool_correctness` metric |
| `coherence` | 1.0 | `coherence` metric |

Signal weights are configurable per eval run and can be overridden via the API.

## Scores

A **score** is the stored result of running one metric against one trace or session.

Scores are what you inspect in the dashboard, query through the API, trend over time, and use for monitoring. Every score contains:

| Field | Description |
|---|---|
| `name` | The metric that produced it (e.g., `task_completion`) |
| `value` | The score value as a string (e.g., `"0.85"`) |
| `data_type` | `NUMERIC` (0–1 float), `BOOLEAN` (`true`/`false`), or `CATEGORICAL` |
| `source` | `AUTOMATED` (from eval run), `ANNOTATION` (human), or `PROGRAMMATIC` (SDK) |
| `status` | `SUCCESS`, `FAILED`, or `PENDING` |
| `reason` | LLM-generated explanation of the score |
| `metadata` | Rich structured data (threshold, intermediate results, signal breakdowns) |
| `eval_run_id` | Links back to the originating eval run (null for manual scores) |

### Score sources

Scores can originate from three places:

- **Automated** — produced by an eval run
- **Annotation** — created or edited by a human in the dashboard
- **Programmatic** — submitted via the SDK or API (e.g., from a CI pipeline)

## Thresholds

Each metric has a **default threshold** that defines what counts as passing. A score at or above the threshold is considered successful.

Thresholds can be overridden per eval run. This lets you change your quality bar without changing the metric itself.

<Info>
  The threshold does not change the score value. It only changes the pass/fail interpretation stored in score metadata.
</Info>

## Signals

A **signal** is a trace-level score that can be reused as input for session-level evaluation.

For example, session evaluation uses `confidence`, `loop_detection`, `tool_correctness`, and `coherence` as signals. These signals are computed for each trace in the session, then aggregated into `agent_reliability` and `agent_consistency`.

This two-step model keeps session evaluation explainable: a low session score can be traced back to the specific traces and signals that caused it.

## Monitors

A **monitor** is a saved evaluation configuration that runs on a recurring schedule. It combines:

- **Target type** — `TRACE` or `SESSION`
- **Metrics** — which metrics to run
- **Filters** — which data to evaluate
- **Cadence** — how often to run (`every_6h`, `daily`, `weekly`, or custom cron)
- **Sampling rate** — fraction of matching data to evaluate
- **`only_if_changed`** — skip the run if no new data has arrived since the last run

Monitors have their own lifecycle (`ACTIVE`, `PAUSED`) and can be triggered manually outside their normal schedule.


## Next steps

<CardGroup cols={2}>
  <Card title="Trace Evaluation" icon="route" href="/evaluation/trace-evaluation/introduction">
    Dive into how trace-level metrics work.
  </Card>
  <Card title="Agent Evaluation" icon="bot" href="/evaluation/agent-evaluation/introduction">
    Learn about session-level aggregation metrics.
  </Card>
</CardGroup>
