# File Tools
phi-agent gives the agent read/write/list access to the filesystem through kernel tools. Enabled by default; can be toggled via the `file` feature flag.
## Available tools
| `read_file` | Read a file, with optional offset/limit for paging large files |
| `write_file` | Create or overwrite a file |
| `list_files` | List directory contents, supports glob patterns |
## Design principles
**Path safety**. All paths are resolved relative to the working directory. Parent directory traversal (`..`) is rejected.
**Size limits**. `read_file` defaults to 2000 lines per call (use `offset`/`limit` for large files). `write_file` defaults to 1MB max per write.
**Explicit truncation**. When `write_file` truncates output, the result carries a `... (truncated)` marker so the agent knows the content is incomplete.
## Usage
The file tools are registered automatically by `base_agent_builder()` — they are enabled by default, no configuration needed:
```toml
# File tools are in the default feature set; explicit declaration is optional
[dependencies]
phi-agent = { version = "0.9", features = ["file"] }
```
```rust
let builder = base_agent_builder(llm_client)
.system_prompt(build_system_prompt());
// read_file, write_file, list_files are registered
```
To disable file tools:
```toml
# Cargo.toml
[dependencies]
phi-agent = { version = "0.9", default-features = false, features = ["shell"] }
```
## Why file tools matter
File tools are the architectural foundation for Skills and Memory: one set of generic file operations replaces multiple dedicated tools. The agent reads and writes the filesystem directly — the framework is the OS.
```mermaid
graph TD
FT["📁 read_file / write_file / list_files<br/><i>File Tools (kernel layer)</i>"]
FT --> SKILLS["Skills<br/>Reads SKILL.md for domain knowledge"]
FT --> MEMORY["Memory<br/>Reads/writes .phi/memory/ for persistent context"]
FT --> RULES["Rule Injection<br/>Reads CLAUDE.md and project rules"]
FT --> CONFIG["Config / Session<br/>Reads project config and session state"]
```
This is the same pattern used by Claude Code and Codex: the agent interacts with the project through standard file operations — no dedicated tools for each resource type.