> For the complete documentation index, see [llms.txt](https://docs.getlynk.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.getlynk.ai/api-reference/api.md).

# API Reference

**Interfaces for querying and managing your Lynk semantic layer.**

This section documents the programmatic interfaces exposed by Lynk — how to write queries against your semantic layer, and how to call Lynk's HTTP endpoints to validate semantics, manage schemas, and inspect the data catalog.

***

## What's in this section

| Page                                       | What it covers                                                                                                                                                                                      |
| ------------------------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| [Lynk SQL](/api-reference/api/lynk-sql.md) | The SQL dialect the agent uses internally and you use when writing evaluation test cases — entity references, `METRIC('<metric_name>')`, joins (default, `USING`, `ON`), CTEs, supported statements |
| [REST API](/api-reference/api/rest-api.md) | HTTP endpoints for validating the semantic layer, managing schemas, and inspecting the data catalog (sources and columns)                                                                           |

***

**Where to go next:**

* Need to understand how entities and metrics are defined? → [Concepts](/concepts/concepts.md)
* Writing evaluation test cases that use Lynk SQL? → [Evaluations YAML](/file-types-reference/file-types/evaluations-yaml.md)


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.getlynk.ai/api-reference/api.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.