Skill vs Subagent vs MCP Picker

Why picking the right tool matters

Claude Code ships with a small set of built-in tools, and each one is sharp at exactly one job. The difference between a fast, clean session and a slow, messy one is often just tool choice. Using Bash to grep through files when Grep exists, or reading an entire directory when you already know the one file you need, wastes tokens and clutters the context. This picker maps your intent to the tool that was built for it, and flags the common mis-picks so you avoid them.

The logic here is deterministic - the same answers always produce the same recommendation, because the right tool for a given need is not a matter of taste. Once you internalize the mapping, you stop reaching for the general-purpose hammer (Bash) for jobs the specialized tools do better.

The built-in tools at a glance

• Read - open a specific file when you already know its path. The default for looking at known files.
• Edit - make a targeted change to an existing file. You must Read it first so the edit matches exactly. Only sends the diff, which is cheaper than rewriting.
• Write - create a new file or fully replace one. Prefer Edit for modifying existing files.
• Grep - search inside files for text or a regex pattern. Built on ripgrep; use it instead of grep/rg through Bash.
• Glob - find files by name or path pattern like **/*.ts. Use it instead of find or ls.
• Bash - run commands: tests, builds, git, scripts. Not for reading, searching, or editing files - the dedicated tools win there.
• WebFetch / WebSearch - pull content from the internet. WebFetch for a known URL, WebSearch to find pages first.
• Agent - delegate an open-ended, multi-step task to a subagent that runs the search-read loop in its own context.

Read vs Grep vs Glob - the trio people confuse

These three cover 'I need to find or look at code' and they are not interchangeable. Read is for when you already know the path - no searching involved. Grep is for when you know what the code says but not where it is - it searches file contents. Glob is for when you know the file's name or shape but not its location - it searches paths. If you find yourself running ls or find or grep through Bash, one of these three is the tool you actually wanted.

When to reach for an Agent instead

The Agent tool is for open-ended work that needs several rounds of searching and reading before you can answer - 'how does auth flow through this codebase', 'find everywhere this pattern is used and summarize'. A subagent runs that loop in its own context and hands back a summary, so your main session is not flooded with every intermediate file. The rule of thumb: if you can name the file or the exact pattern, use the direct tool; if you need to explore to even know what to look at, use an Agent.

Edit vs Write

1. Modifying an existing file - use Edit. It does a precise string replacement and only transmits the change, so it is cheaper and less error-prone than resending the whole file.
2. Read before you Edit - Edit requires that you have read the file so the match is exact. Skipping the read is the usual cause of a failed edit.
3. Creating a brand-new file - use Write. There is nothing to diff against.
4. A complete rewrite of an existing file - Write is acceptable, but prefer Edit when the change is localized.
5. Never edit with Bash sed/awk - Edit is the correct, reviewable tool for changing file contents.

Web tools: WebFetch vs WebSearch

When the information you need lives on the internet rather than in your repo, use the web tools. WebFetch retrieves a specific URL you already have - documentation, an issue, a spec. WebSearch is for when you do not have the URL and need to find relevant pages first. The key discrimination is: if the answer is in your codebase, Grep and Read are faster and do not leave the machine; only go to the web when the repo genuinely does not have it.

A quick mental model to keep

• Know the path -> Read.
• Know the text, not the location -> Grep.
• Know the filename shape, not the location -> Glob.
• Changing a file -> Edit (Read it first); new file -> Write.
• Running a command -> Bash.
• It is on the web -> WebFetch (have URL) or WebSearch (need URL).
• Have to explore to even know where to look -> Agent.