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

# Tools Overview

> How Isthmus MCP tools work and the recommended discovery workflow.

Isthmus exposes three MCP tools that AI models call to explore and query your PostgreSQL database. You don't call these tools directly — your AI client (Claude, Cursor, etc.) invokes them automatically based on your questions.

## Recommended discovery workflow

When an AI model connects to your database for the first time, the most effective sequence is:

```
1. discover          → What schemas and tables exist? (sizes, row counts, columns)
2. describe_table    → Full table analysis: columns, types, keys, stats, sample rows, index usage
3. query             → Execute a read-only SQL query (with optional EXPLAIN plan)
```

Most AI models follow this pattern naturally — they start broad with `discover`, narrow down to specific tables with `describe_table`, then write and execute SQL with `query`.

## Tool summary

| Tool                                      | Purpose                                                                | Parameters                             |
| ----------------------------------------- | ---------------------------------------------------------------------- | -------------------------------------- |
| [`discover`](/docs/tools/discover)             | Full database landscape: schemas with nested tables                    | *(none)*                               |
| [`describe_table`](/docs/tools/describe-table) | Complete table analysis: columns, statistics, sample rows, index usage | `table_name` (required), `schema`      |
| [`query`](/docs/tools/query)                   | Execute read-only SQL with optional EXPLAIN plans                      | `sql` (required), `explain`, `analyze` |

## Safety guardrails

All tools operate within Isthmus's safety model:

* **Read-only transactions** — queries cannot modify data
* **SQL validation** — only `SELECT` and `EXPLAIN` statements are allowed (enforced via PostgreSQL AST parsing)
* **Row limits** — configurable max rows per query (default: 100)
* **Query timeout** — configurable timeout (default: 10s)
* **Schema filtering** — only expose the schemas you choose

See [Security](/docs/security) for the full safety model.