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

# Compatibility policy

> The public API and capability contract for the 0.4 release line.

This policy applies to the **0.4.x** release line across Rust, Python, Node.js,
and browser WASM. Version 0.4.0 is published for all four runtimes.

## Stable within 0.4.x

Existing public function signatures, required finding fields, documented error
and exception interfaces, and offset semantics remain compatible throughout
0.4.x. Byte ranges use UTF-8 bytes, code-point ranges use Unicode code points,
and JavaScript UTF-16 ranges use UTF-16 code units. Every range is zero-based
and end-exclusive. Structured finding ranges remain local to the string leaf
identified by the JSON Pointer path.

Breaking changes to a binding's existing public interface require **0.5.0**.
This includes removing or renaming required finding fields, changing existing
argument requirements, or changing the documented error or range contract.

## Additions and detector changes

New entity labels, supported locales, API entry points, and optional metadata
fields are compatible additions. Consumers should tolerate unknown optional
metadata and use the Rust/Python capability API when choosing detectors. Do not infer
capabilities solely from a package version or maintain a private copy of the
supported-label inventory.

Detection results are data-dependent. Detector fixes and improvements can change
which findings are returned, including correcting false positives or missed
matches. A compatible API does not guarantee identical findings for every input
across patch releases. Pin package versions and maintain representative fixtures
when exact detection output is part of an application's acceptance criteria.

## Capability contract version

The capability response carries `contract_version: 1`. This version identifies
the meaning and structure of the capability contract, independently of the
package version. Compatible additions such as an additional entity, locale, or
optional metadata field retain contract version 1. Changes to existing capability
field meanings or incompatible structure require a contract-version increment.

See the [capabilities reference](/reference/capabilities) for the generated
inventory and activation metadata. The [0.4.0 release notes](/releases/0-4-0)
identify the intentional locale-validation change introduced at the release
boundary.