Built-in tools

Skiller ships two language-model tools that write to the filesystem: skiller_createFile and skiller_replaceInFile. They are always available — no MCP server to configure — so a skill can produce files with zero setup. Use them from a tool step in a skill, or reference them directly in chat (e.g. @skiller #createFile).

Why these exist

VS Code’s built-in file-editing tools (such as copilot_createFile) rely on internal Copilot chat context that is not passed to third-party chat participants when they are invoked through the Language Model Tools API. Calling them from @skiller fails (for example, with an “Invalid stream” error). Skiller therefore ships its own file tools that work reliably in any context — both inside a skill’s tool step and when invoked from chat.

Workspace confinement

By default, both tools refuse to write outside the open workspace folder. A path that escapes the workspace — via .., an absolute path elsewhere, or a different drive — is rejected, which guards against a shared or forked skill targeting arbitrary paths like ~/.ssh/config.

To allow writes anywhere, set skiller.skills.allowOutsideWorkspaceWrites to true. With no workspace folder open and the setting off, the tools error rather than fall back to writing relative to an unknown location.

Caution

skiller.skills.allowOutsideWorkspaceWrites is a security control. Leave it false unless you explicitly trust every skill that can run, since it lets the file tools write anywhere on disk.

skiller_createFile

Creates a file at the given path with the given content, overwriting it if it already exists. Parent directories are created as needed.

Parameter	Type	Required	Description
filePath	string	yes	Where to create the file. Absolute, or relative to the workspace folder.
content	string	yes	The full text to write. An empty string creates an empty file.

Returns a confirmation message with the resolved path on success, or an error message (for example, when the path escapes the workspace).

Calling it from a tool step through a tools.aliases entry:

tools:
  aliases:
    create_file: skiller_createFile     # alias -> built-in LM tool
steps:
  - id: save
    type: tool
    tool: create_file
    params:
      filePath: "notes.md"
      content: "{{ outputs.draft.text }}"
    output: saved

skiller_replaceInFile

Replaces every occurrence of an exact search string with a replacement string inside an existing file. Prefer it over rewriting the whole file when a skill edits a document across several steps — it avoids re-sending the entire content each time. It errors if the file does not exist or if the search string is not found.

Parameter	Type	Required	Description
filePath	string	yes	The file to modify. Absolute, or relative to the workspace folder.
search	string	yes	The exact text to find. Every match is replaced (not a regex).
replace	string	yes	The text to substitute for each match.

A common pattern is to seed a file with [[PLACEHOLDER]] markers via skiller_createFile, then have later steps swap each marker for generated content:

tools:
  aliases:
    replace_in_file: skiller_replaceInFile
steps:
  - id: fill-summary
    type: tool
    tool: replace_in_file
    params:
      filePath: "report.md"
      search: "[[SUMMARY]]"
      replace: "{{ outputs.summary }}"
    output: filled

Where to use them

• In a skill — alias a tool under tools.aliases and call it from a tool step. The step’s params are Liquid-interpolated, so you can wire in {{ inputs.* }} and {{ outputs.* }} values.
• In chat — both tools are referenceable in a prompt (#createFile, #replaceInFile), so the model can call them while answering a request.

Related

• Build a tool/MCP skill — a full, copyable skill that drafts text and writes it with skiller_createFile.
• skill.yaml reference — the tool step and tools.aliases schema.
• Settings — skiller.skills.allowOutsideWorkspaceWrites.