btw 1.2.0

Breaking changes

• Several tool groups and tool names have been renamed for clarity (#159):

  Old Name	New Name
  session group	sessioninfo group
  search group	cran group
  btw_tool_session_platform_info()	btw_tool_sessioninfo_platform()
  btw_tool_session_package_info()	btw_tool_sessioninfo_package()
  btw_tool_session_check_package_installed()	btw_tool_sessioninfo_is_package_installed()
  btw_tool_search_packages()	btw_tool_cran_search()
  btw_tool_search_package_info()	btw_tool_cran_package()
  btw_tool_files_list_files()	btw_tool_files_list()
  btw_tool_files_read_text_file()	btw_tool_files_read()
  btw_tool_files_write_text_file()	btw_tool_files_write()
  btw_tool_files_code_search()	btw_tool_files_search()

  The old names and group aliases continue to work but emit deprecation warnings. The btw.files_code_search.extensions and btw.files_code_search.exclusions options have also been renamed to btw.files_search.extensions and btw.files_search.exclusions, with the old option names emitting deprecation warnings.

New features

• New btw CLI provides command-line access to btw’s tool groups — docs, pkg, info, and cran — powered by Rapp. Install with install_btw_cli() and run commands like btw docs help dplyr::mutate or btw cran search "tidyverse". Output is designed for humans and LLMs: colored and formatted for terminals, plain markdown when piped, with a --json flag to return pipable JSON in select commands (#176).

• btw.md now supports configuring multiple client options. When btw_client() is called interactively, you’ll be presented with a menu to choose which client to use. Clients can be specified as an array:

  client:
    - anthropic/claude-sonnet-4
    - openai/gpt-4.1
    - aws_bedrock/us.anthropic.claude-sonnet-4-20250514-v1:0

  Or as named aliases:

  client:
    haiku: aws_bedrock/us.anthropic.claude-haiku-4-5-20251001-v1:0
    sonnet: anthropic/claude-sonnet-4
    chatgpt: openai/gpt-5.2

  With aliases, you can select a client by name in the interactive menu or pass the alias directly via btw_client(client = "alias"). In non-interactive contexts, the first client is used automatically (#153).

• btw_agent_tool() allows you to create specialized custom subagents from btw.md style markdown files. Agent files are automatically discovered from .btw/agent-*.md (project and user directories) and .claude/agents/ (for Claude Code compatibility), and are registered as callable tools in btw_tools(). Custom agents can specify their own system prompts, icons, models, and available tools (#149).

• btw_task() runs pre-formatted LLM tasks defined in markdown files with YAML frontmatter. Task files support template variable interpolation via {{ variable }} syntax, optional client and tool configuration, and all four execution modes ("app", "console", "client", "tool"). Task files can also specify title, icon, description, and name fields in their YAML frontmatter to customize the tool definition when used in "tool" mode (#169).

• btw_tool_agent_subagent() enables hierarchical agent workflows by allowing an orchestrating LLM to delegate tasks to subagents. Each subagent runs in its own isolated chat session with restricted tool access and maintains conversation state that can be resumed via session_id. This allows you to delegate tasks to smaller cheaper models or reduce context bloat in the main conversation (#149).

• btw_tool_files_edit() makes targeted, validated line-based edits to files using replace, insert_after, and replace_range actions. Edits are anchored to content hashes, so stale edits are rejected if the file has changed. To support this, btw_tool_files_read() now annotates each line with a short hash (e.g. 2:f1a| return("world")) when called as a tool (#167).

• btw_tool_files_replace() finds and replaces exact string occurrences in a file. By default it requires the string to appear exactly once to prevent unintended changes; set replace_all = TRUE to replace all occurrences (#167).

• btw_tool_pkg_load_all() runs pkgload::load_all() in an isolated subprocess to verify package code loads correctly and trigger recompilation of compiled code. Useful for quick validation during development without running full tests or affecting the current R session (#156).

• btw_tool_skill() adds support for Agent Skills. Skills are modular, on-demand capabilities that provide specialized instructions, bundled scripts, reference docs, and asset templates to the LLM. Skills are discovered automatically from the btw package, attached R packages with inst/skills/ directories, user-level skills, and project-level skills in .btw/skills/ or .agents/skills/. When the skill tool is included in the chat client, available skills are listed in the system prompt. Use btw_skill_install_github() or btw_skill_install_package() to install skills from external sources, and btw_task_create_skill() to interactively create new skills (#145).

Bug fixes

• btw_app() no longer errors with “argument is of length zero” when run outside of an IDE (thanks @HenrikBengtsson, #168).

• btw_app() no longer errors when provider built-in tools (e.g. claude_tool_web_search()) are registered with a btw client. Built-in tools now appear in the app sidebar under a “Built-in” group (#175).

• btw_tool_files_read() now correctly handles UTF-8 files containing CJK (Chinese, Japanese, Korean) characters. Previously, the text-file detection could truncate a read buffer mid-way through a multi-byte character, causing the file to be rejected as binary (thanks @bianchenhao, #170).

• btw_tool_files_read() now correctly reads valid UTF-8 files containing non-ASCII characters (e.g., Cyrillic). Previously, these files were incorrectly rejected on Windows with non-English locales when Encoding() returned “unknown” even though they were valid UTF-8 (thanks @RKonstantinR, #160).

btw 1.1.0

• btw_client() now supports reading CLAUDE.md files as project context files. CLAUDE.md files are searched after AGENTS.md but before user-level btw.md. YAML frontmatter in CLAUDE.md files is stripped but not used for configuration (#146).

• btw_app() now shows a rich diff view in the btw_tool_files_write_text_file() tool, if the {diffviewer} package is installed (#144).

• btw() now correctly handles character matrices (#139).

• btw_app() now correctly displays input tokens with ellmer v0.4.0. Previously, we were showing the total input tokens sent across all API calls, rather than the current number of input tokens as of the last API call. We now show the size of the input context window (i.e. the number of input tokens that will be used for the conversation history in the next API call). Note that token usage is dependent on the provider and model used and is only an estimate.

• New “pkg” tool group with package development tools: btw_tool_pkg_document(), btw_tool_pkg_check(), btw_tool_pkg_test() and btw_tool_pkg_coverage() provide LLMs with the ability to document, check, test, and check test coverage of R packages during development (#133, #136).

• New btw_tool_run_r() tool allows LLMs to run R code and to see the output, including of plots. Because this tool lets LLMs run R arbitrary R code in the global environment (which can be great but can also have security implications), it is opt-in and disabled by default. See ?btw_tool_run_r for more details (#126).

• btw_tool_docs_help_page() now uses markdown headings and sections for argument descriptions, rather than a table. This is considerably more token efficient when the argument descriptions have more than one paragraph and can’t be converted into a markdown table (@jeanchristophe13v, #123).

• btw now removes large inline base64-encoded images, replacing them with a placeholder containing the image’s alt text (@jeanchristophe13v, #119).

• btw_app() now works correctly with {ellmer} v0.4.0 (#121).

• btw_app() now shows more precise cost estimates when the cost is less than $0.10 (#121).

btw 1.0.0

• Initial CRAN submission.