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Built-in Tools

Tools allow the LLM to perform actions in your codebase. CoStrict ships with a set of built-in tools and can be extended via custom tools or MCP servers.

By default, all tools are enabled and require no permission to run. Use permissions to control tool behavior.

Tool Permission Configuration​

Use the permission field to control tool behavior:

costrict.json
{
  "$schema": "https://opencode.ai/config.json",
  "permission": {
    "edit": "deny",
    "bash": "ask",
    "webfetch": "allow"
  }
}

Use wildcards to control multiple tools at once — for example, require confirmation for all tools from an MCP server:

costrict.json
{
  "$schema": "https://opencode.ai/config.json",
  "permission": {
    "mymcp_*": "ask"
  }
}

Built-in Tool Reference​

bash​

Execute shell commands in the project environment (npm install, git status, etc.).

edit​

Modify existing files via exact string replacement. The primary way the LLM changes code.

write​

Create new files or overwrite existing ones.

The write tool is controlled by the edit permission, which covers all file modification operations: edit, write, patch, and multiedit.

read​

Read file contents. Supports reading a specific line range in large files.

grep​

Search file contents with regular expressions. Supports full regex syntax and file pattern filtering.

glob​

Find files by pattern. Supports **/*.js, src/**/*.ts, etc. Returns results sorted by modification time.

list​

List files and directories at a given path. Supports glob pattern filtering.

patch​

Apply a patch (diff) file to the codebase.

The patch tool is controlled by the edit permission.

webfetch​

Fetch and read web page content — useful for consulting documentation or researching online resources.

websearch​

Search the web for information.

Available only when using the CoStrict platform provider, or when COSTRICT_ENABLE_EXA=1 is set.

skill​

Load a Skill file (SKILL.md) and return its contents in the conversation.

todowrite​

Create and update a to-do list during coding sessions to track progress on complex multi-step tasks.

Disabled by default for sub-agents. Can be enabled in agent configuration.

todoread​

Read the current state of the to-do list.

Disabled by default for sub-agents. Can be enabled in agent configuration.

lsp (experimental)​

Interact with configured LSP servers for code intelligence: go-to-definition, find references, hover info, call hierarchy, and more.

Enable with:

export COSTRICT_EXPERIMENTAL_LSP_TOOL=true

Supported operations: goToDefinition, findReferences, hover, documentSymbol, workspaceSymbol, goToImplementation, prepareCallHierarchy, incomingCalls, outgoingCalls.

question​

Ask the user a question during task execution — useful for gathering preferences, clarifying instructions, or requesting decisions. Supports single-choice and free-text input.

Ignore Patterns​

Tools like grep, glob, and list use ripgrep under the hood, which respects .gitignore patterns by default.

To include files that would normally be ignored, create an .ignore file in the project root:

.ignore
!node_modules/
!dist/
!build/

Extending Tools​

  • Custom tools: Write TypeScript/Python functions for the LLM to call — see Custom Tools
  • MCP servers: Integrate external tools and services — see MCP Servers