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read_file

The read_file tool reads file contents and returns them with line numbers. It supports reading entire files or specific line ranges.

Description

Read the contents of a file at the specified path. Returns the file content with line numbers for easy reference.

Parameters

ParameterTypeRequiredDescription
pathstringYesThe path to the file to read
start_lineintegerNoStarting line number (1-indexed)
end_lineintegerNoEnding line number (1-indexed, inclusive)

Examples

Read Entire File

you: Show me the config file


ai: I'll read the configuration file.


[tool: read_file]
  path: "src/config.rs"


   1 | use serde::Deserialize;
   2 |
   3 | #[derive(Debug, Deserialize)]
   4 | pub struct Config {
   5 |     pub api_key: String,
   6 |     pub model: String,
   7 | }

Read Specific Lines

you: Show me lines 10-20 of main.rs


ai: I'll read lines 10 through 20.


[tool: read_file]
  path: "src/main.rs"
  start_line: 10
  end_line: 20


  10 | fn process_input(input: &str) -> Result<()> {
  11 |     let trimmed = input.trim();
  12 |     if trimmed.is_empty() {
  13 |         return Ok(());
  14 |     }
  15 |     // Process the input
  16 |     handle_command(trimmed)
  17 | }

Output Format

The output includes:

  • Line numbers (right-aligned, 4 characters)
  • Pipe separator
  • Actual line content
   1 | first line
   2 | second line

For empty files, returns (empty file).

Error Handling

Common errors:

ErrorCause
Failed to read file: No such file or directoryFile doesn’t exist
Failed to read file: Permission deniedNo read permission
Failed to read file: Is a directoryPath is a directory, not a file

Best Practices

  1. Start broad, then narrow

    • First read the whole file to understand structure
    • Then request specific line ranges for focused work

  2. Use for context

    • Read related files before making edits
    • Helps the AI understand dependencies and patterns

  3. Combine with grep

    • Use grep to find where something is
    • Then read_file with line range to see context