LLM Tools for Go

Go-native, cross-platform tools for common local tasks, plus a small registry that makes them easy to expose to LLM tool-calling systems.

Table of contents

• Features at a glance
  • File system tools
  • Execute tools
  • Text processing tools
  • Image tools
  • Git tools
  • Web fetching tools
• Package overview
• Registry
• Tool outputs
• Path policy
• Examples
• Exec tool notes
  • Quick model
  • Shell selection and bootstrap defaults
  • Working directory behavior
  • Environment behavior
  • Shell sessions: what persists and what does not
  • Command lookup and login-shell behavior
  • Run Script behavior
  • Execution limits and blocking
  • Important behavioral notes
• Development
• License

Features at a glance

• Cross-platform implementations for Linux, macOS, and Windows.
• Instance-owned tools with configurable path policy.
• Deterministic text-editing and unified-diff patching tools for line-oriented workflows.
• Shell command and script execution with timeouts, output caps, and command blocking.
• Structured tool manifests and normalized outputs for text, files, and images.

File system tools

Grouped under fstool.

• readfile

  • encoding=text: reads UTF-8 text and supports extracted text for PDFs.
  • encoding=binary: returns base64, emitting image outputs for image/* MIME types and file outputs otherwise.
  • Safety: size caps and symlink hardening.

• writefile

  • encoding=text: write UTF-8 content.
  • encoding=binary: write base64-decoded bytes.
  • Options: overwrite, createParents (bounded), atomic writes, size caps, symlink hardening.

• deletefile

  • Safe delete by moving to trash.
  • trashDir=auto tries system trash when possible and otherwise falls back to a local .trash directory.

• searchfiles: recursively search file paths and UTF-8 text content using RE2 regex.

• listdirectory: list entries under a directory, optionally filtered by glob.

• statpath: inspect a path.

• mimeforpath: best-effort MIME type detection.

• mimeforextension: MIME lookup for an extension.

Execute tools

Grouped under exectool.

• shellcommand

  • Execute one or more shell commands via a selected shell.
  • Supports session-like persistence for workDir and env across calls.
  • Sessions are not persistent shell processes.

• runscript

  • Run an existing script from disk with arguments and environment overrides.
  • Uses extension-based interpreter selection via RunScriptPolicy.

Text processing tools

Grouped under texttool.

• readtextrange: read n text lines from a line number.
• findtext: find matches with context.
• inserttext: insert text at start/end/between text blocks.
• replacetext: replace text, with optional disambiguation using above/below text.
• deletetext: delete text, with optional disambiguation using above/below text.
• applyunifieddiff
  • Apply or dry-run Git-style unified diffs against local UTF-8 text files.
  • Supports multi-file patches, create/delete edits, mode-only changes, no-newline-at-EOF markers, and safe fuzzy hunk matching.
  • Accepts explicit fileTargets when diff paths are missing, wrong, relative to a different base, or ambiguous.
  • Accepts optional candidatePaths to help resolve patch targets by exact path, suffix, or unique basename.
  • Tracks already-applied changes and returns structured per-file results plus reusable fileTargets.
  • Set dryRun=true to inspect applicability without writing files.
  • Set strict=true to require exact hunk matching only.
  • The parser is intentionally tolerant of common malformed or LLM-generated diffs.

Image tools

Grouped under imagetool.

• readimage: read intrinsic metadata and optionally include base64 content.

Git tools

• gittool provides pure-Go local Git repository inspection and editing.
• Read-oriented tools include gitstatus, gitdiff, gitlog, gitshow, gitbranch, gittag, gitchangedfiles, gitlisttree, gitreadblob, gitfindrepos, gitblame, gitfilehistory, gitrepoinfo, and gitgrep.
• Write-oriented tools include gitadd, gitreset, gitcommit, gitinit, gitcreatebranch, gitcheckout, gitcreatetag, and gitdeletetag.

Web fetching tools

• webtool provides fetchurl for HTTP and HTTPS URLs.
• In auto mode, HTML, text, and PDF responses return compact text, while binary responses return image or file outputs.
• fetchurl also supports encoding=text and encoding=binary, startIndex for truncated text continuation, and raw=true for decoded text without Markdown extraction.
• By default, localhost, private, link-local, multicast, and reserved addresses are blocked and redirects are revalidated.

Package overview

• llmtools: registry and tool registration helpers.
• spec: tool manifests and output union types.
• fstool: filesystem tools.
• exectool: shell command execution and script execution.
• texttool: safe, deterministic line-based text editing and unified-diff patching tools.
• imagetool: image tools.
• gittool: pure-Go local Git repository tools for reading, editing, and history inspection.
• webtool: HTTP/HTTPS fetching with compact text extraction and binary/file outputs.

Registry

The registry provides:

• tool registration and lookup by spec.FuncID
• stable manifest ordering (Tools() sorted by slug + funcID)
• per-registry default call timeout via WithDefaultCallTimeout
• per-call timeout override via llmtools.WithCallTimeout(...)
• panic-to-error recovery around tool execution
• builtin registration for filesystem, image, execute, git, text, and web fetch tools via NewBuiltinRegistry()

Tool outputs

• Registry.Call returns []spec.ToolOutputUnion.
• Most tools are registered via RegisterTypedAsTextTool, which wraps the Go result as JSON and returns it as a single text output item.
• Tools that naturally return binary or image data can emit typed image or file outputs.

Path policy

All tools are instance-owned. Hosts can configure:

• workBaseDir: base directory for resolving relative paths
• allowedRoots: optional allowlist roots; when set, resolved tool paths must stay within these roots
• blockSymlinks: optional symlink hardening for supported operations

This is path policy, not a general OS sandbox for child processes.

Examples

All examples are provided as end-to-end integration tests that:

• start from a registry
• register tools scoped to a temp directory
• execute realistic read/modify loops, text edits, shell sessions, script execution, and binary/image workflows

Examples:

• Text read/modify loop: text test
• Filesystem, MIME, safe delete, binary, and image flows: fs + image test
• Shell sessions, environment persistence, and runscript: exec test

Exec tool notes

Quick model

For exectool, the most useful mental model is:

• workBaseDir chooses the default base for relative paths.
• shellcommand.workDir chooses the actual child-process working directory.
• shellcommand.env and runscript.env add per-call environment overrides.
• Shell sessions persist tool-managed workDir and env, not shell process state.
• Commands are executed in fresh child processes, not in a long-lived interactive terminal.

Shell selection and bootstrap defaults

shellcommand supports explicit shell selection with:

• auto
• bash, zsh, sh, dash, ksh, fish
• pwsh, powershell, cmd

ExecTool also supports tool-level defaults:

• WithDefaultShell(...)
• WithBaseEnv(...)

If the caller does not provide them, NewExecTool(...) best-effort bootstraps defaults:

• detects a preferred shell
• captures a narrow, execution-oriented base environment

Auto shell detection order is:

• Unix/macOS:
  1. $SHELL
  2. account login shell from the host
  3. fallback by platform/tool availability
• Windows:
  1. pwsh
  2. powershell
  3. cmd

You can also call BootstrapDefaults(ctx) directly and pass the results yourself.

ctx := context.Background()
defs, _ := exectool.BootstrapDefaults(ctx)

tool, err := exectool.NewExecTool(
   exectool.WithWorkBaseDir(projectDir),
   exectool.WithDefaultShell(defs.DefaultShell),
   exectool.WithBaseEnv(defs.BaseEnv),
)

Working directory behavior

shellcommand resolves working directory in this order:

1. args.workDir
2. session workdir
3. tool workBaseDir

Key points:

• If workDir is omitted and there is no session workdir, execution starts in the tool workBaseDir.
• If workBaseDir is omitted, the path policy falls back to the current process working directory unless allowedRoots is set, in which case it defaults to the first canonical allowed root.
• Relative paths are resolved against workBaseDir unless a more specific absolute/derived path is supplied by the tool logic.

For stable desktop-app behavior, hosts should usually:

• set workBaseDir explicitly
• pass an absolute per-call workDir for the active project/workspace

Environment behavior

Effective environment merge order is:

• shellcommand

  1. current process environment
  2. tool base env (WithBaseEnv or bootstrapped defaults)
  3. session env
  4. per-call env

• runscript

  1. current process environment
  2. tool base env (WithBaseEnv or bootstrapped defaults)
  3. per-call env

Bootstrapped base env is intentionally filtered. It keeps variables that are usually relevant to command and interpreter resolution, for example:

• command lookup: PATH, PATHEXT
• home/temp/runtime basics: HOME, USERPROFILE, TMP, TEMP, TMPDIR, SHELL, COMSPEC, app-data dirs
• locale basics: LANG, LC_*, TERM
• common toolchain/version-manager variables: ASDF_*, PYENV_*, NVM_*, VOLTA_*, SDKMAN_*, GOPATH, GOBIN, JAVA_HOME, PNPM_HOME, CARGO_HOME, CONDA_*

This avoids importing unrelated prompt/theme variables while still making command lookup and common toolchains behave more like the user’s shell.

Shell sessions: what persists and what does not

shellcommand sessions are persistent tool state, not persistent shell processes.

What persists across calls when you reuse sessionID:

• workDir passed as a tool argument
• env passed as a tool argument

What does not persist:

• cd ... issued inside a command string
• export FOO=... issued inside a command string
• aliases, functions, shell options, sourced files
• any in-memory shell state

So this works predictably:

{
  "workDir": "/repo",
  "commands": ["go test ./..."]
}

But this is not persistent across separate command entries or later calls:

{
  "commands": ["cd /repo", "go test ./..."]
}

Each command entry is executed in a fresh shell process.

Command lookup and login-shell behavior

Working directory and command lookup are separate concerns.

• Working directory controls where the child process starts.
• Command lookup for bare names like golangci-lint depends on PATH and shell behavior.

Important nuance:

• Commands are executed using non-persistent shell invocations.
• You should not assume they behave exactly like an interactive terminal.
• On Unix, zsh -c/bash -c behavior differs from an interactive login terminal.
• On PowerShell, execution uses explicit non-interactive flags.

That is why BootstrapDefaults(...) exists: it captures a stable, tool-useful environment once, instead of relying on every command to run as an interactive login shell.

For predictable command execution, hosts should prefer:

• explicit workDir
• explicit or bootstrapped base env
• explicit shell or WithDefaultShell(...)
• absolute executable paths when needed

Run Script behavior

runscript:

• executes a pre-existing script from disk
• validates the script path through path policy
• selects how to invoke the script from RunScriptPolicy

Default policy includes mappings such as:

• .sh -> shell mode with sh
• .bash -> shell mode with bash
• .zsh -> shell mode with zsh
• .ps1 -> direct PowerShell execution
• .py -> interpreter mode with python3 on Unix and python on Windows

Behavioral notes:

• runscript inherits tool base env and per-call env.
• Interpreter availability still depends on the effective environment, especially PATH.

Execution limits and blocking

ExecutionPolicy controls:

• timeout
• output caps
• max commands
• max command length

There is also a non-overridable hard blocklist of command names and some heuristic blocking for obviously unsafe shell patterns.

The registry may also impose a call timeout. If you use both registry-level and tool-level timeouts, ensure the registry timeout is not shorter than the exec-tool timeout.

Important behavioral notes

• executeParallel=true does not run commands concurrently. It means commands are treated as independent and execution does not stop on the first non-zero result.
• shellcommand executes each command entry separately. If you need shell chaining semantics, put them in one command string, for example cd repo && go test ./....
• workBaseDir is a default anchor, not a persistent current-directory concept by itself.
• If you omit both workBaseDir and allowedRoots, relative/default behavior falls back to the host process working directory.
• If you set allowedRoots but omit workBaseDir, the base defaults to the first canonical allowed root.
• allowedRoots constrains tool-resolved paths; it does not turn child processes into a full OS sandbox.
• For packaged desktop apps, relying on ambient process cwd or ambient process env is usually less stable than passing explicit values.

Development

• Formatting follows gofumpt and golines via golangci-lint. Rules are in .golangci.yml.
• Useful scripts are defined in taskfile.yml; requires Task.
• Bug reports and PRs are welcome:
  • Keep the public API (package llmtools and spec) small and intentional.
  • Avoid leaking provider-specific types through the public surface; put them under internal/.
  • Please run tests and linters before sending a PR.

License

Copyright (c) 2026 - Present - Pankaj Pipada

All source code in this repository, unless otherwise noted, is licensed under the MIT License. See LICENSE for details.