Docs: Refresh docs to organize and standardize reference materials. (#18403)

docs/tools/internal-docs.md

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+# Internal documentation tool (`get_internal_docs`)
+
+The `get_internal_docs` tool lets Gemini CLI access its own technical
+documentation to provide more accurate answers about its capabilities and usage.
+
+## Description
+
+This tool is used when Gemini CLI needs to verify specific details about Gemini
+CLI's internal features, built-in commands, or configuration options. It
+provides direct access to the Markdown files in the `docs/` directory.
+
+### Arguments
+
+`get_internal_docs` takes one optional argument:
+
+- `path` (string, optional): The relative path to a specific documentation file
+  (for example, `cli/commands.md`). If omitted, the tool returns a list of all
+  available documentation paths.
+
+## Usage
+
+The `get_internal_docs` tool is used exclusively by Gemini CLI. You cannot
+invoke this tool manually.
+
+When Gemini CLI uses this tool, it retrieves the content of the requested
+documentation file and processes it to answer your question. This ensures that
+the information provided by the AI is grounded in the latest project
+documentation.
+
+## Behavior
+
+Gemini CLI uses this tool to ensure technical accuracy:
+
+- **Capability discovery:** If Gemini CLI is unsure how a feature works, it can
+  lookup the corresponding documentation.
+- **Reference lookup:** Gemini CLI can verify slash command sub-commands or
+  specific setting names.
+- **Self-correction:** Gemini CLI can use the documentation to correct its
+  understanding of Gemini CLI's system logic.
+
+## Next steps
+
+- Explore the [Command reference](../cli/commands.md) for a detailed guide to
+  slash commands.
+- See the [Configuration guide](../get-started/configuration.md) for settings
+  reference.