> ## Documentation Index
> Fetch the complete documentation index at: https://docs.thrindex.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Conformance Overview

> What THRINDEX Certified means and how the conformance system works.

## The THRINDEX Certified badge

A backend that earns the THRINDEX Certified badge has passed the conformance harness against `CONFORMANCE_ENVELOPE_V0` on the ratified fixture set. This means:

* Its outputs agree with the reference simulator's outputs within precisely stated bounds
* The agreement was measured on a statistically valid fixture set (≥ 100 samples)
* The measurement is reproducible from the frozen fixture set (CRC32 `e2ebd845`)

The badge is per-backend, per-model-class, and per-envelope-version. "THRINDEX Certified \[v0]" means the V0 envelope on the default model class (feedforward LIF, SHD-class).

## The reference simulator

The reference implementation is `thrindex-sim`: a pure software behavioral simulator that runs models in f32. It defines correct behavior. Every hardware backend is certified relative to the reference — the badge means the backend agrees with the simulator within the envelope, not that the backend is equivalent to the simulator.

## The conformance harness

The harness (`thrindex-conformance`) runs both the reference simulator and the backend-under-test on each fixture sample, computes the spike-equivalence metric, and aggregates into `T_mean`, `T_max`, and `P_pred`. It then checks all three against the envelope thresholds.

```bash theme={null}
thrindex bench --conformance --target <backend>
```

Exit code: 0 (PASS), 1 (FAIL), 2 (error).

## Why three metrics?

A single metric is not enough because different failure modes of a hardware backend look different:

* **T\_mean** catches systematic drift — a backend that is consistently wrong by a small amount on every sample
* **T\_max (p99)** catches tail failures — a backend that is mostly correct but occasionally very wrong
* **P\_pred** catches decision-level failures — backends that pass the first two but produce wrong classifications in edge cases

A backend must pass all three simultaneously. Failing any one is a FAIL.

## Envelope versioning

The current envelope is `CONFORMANCE_ENVELOPE_V0`. Future envelopes (`V1`, `V2`, ...) may add model classes (recurrent networks, Conv2d-heavy models) or tighten thresholds as hardware matures.

A backend certified under V0 retains the V0 certification indefinitely. It must be re-certified under V1 to carry the V1 badge.

## The fixture set

The conformance fixture set is a frozen set of 120 SHD test samples in sparse-event JSON format, CRC32-fingerprinted at `e2ebd845`. It lives at `conformance/fixtures/` in the monorepo. The fixture set is:

* **Frozen**: no sample is ever added, removed, or modified after ratification
* **Reproducible**: generated by `freeze_shd_fixtures.py` with seed 0
* **Stratified**: 6 samples per class × 20 classes

See [Conformance: Envelope V0](/conformance/envelope-v0) for the full derivation.