witc

README

witc

A Go CLI that summarizes a codebase for LLM coding agents. It builds a type-checked call graph, extracts the API surface with doc comments, derives package-level architecture, computes metrics, and renders it all as markdown or a versioned JSON schema — with token budgeting so the output fits a context window.

Go only, for now.

Installation

Install a binary via

go install github.com/jomolungmah/witc/main/cmd@latest

Then copy a skill file to agent folder of your choosing, here's an example for OpenCode:

mkdir -p ~/.config/opencode/skills/witc \                                                                                                │
curl -sSL https://raw.githubusercontent.com/jomolungmah/witc/refs/heads/main/.opencode/skill/witc/SKILL.md -o ~/.config/opencode/skills/w
itc/SKILL.md

Also make sure that ~/go/bin is in your $PATH so installed binary will be accessible in your shell.

Usage

witc summarize [path]                  # default: current directory
witc summarize ./myproject -o summary.md
witc summarize . --format json         # versioned JSON (see docs/json-schema.md)
witc summarize . --detail low          # exported API surface only
witc summarize . --max-tokens 4000     # cap output to ~4000 tokens
witc summarize . --no-structure        # omit the file tree
witc summarize . --include-tests       # include _test.go files

Features

Type-checked call graph

Built with go/packages and full type information, so calls resolve to their declared functions and methods:

• Callees resolve to a single shared node — scanner.Scan() and the declared Scan are one function, not two.
• Methods are identified by receiver, e.g. pkg.(*Processor).Process.
• Standard-library and third-party calls are classified by import path and counted as external, instead of guessed from names.

(If a module can't be type-checked, witc falls back to an AST-only graph.)

API surface with documentation

• Structs (fields + methods), interfaces, and functions with their signatures.
• The first sentence of each doc comment (package, type, function, method), which is usually worth more to an agent than the signature alone.
• Exported symbols are listed first; unexported helpers are collapsed at lower detail levels.

Architecture overview

• Entry points (functions nothing in the module calls, plus main).
• A per-package line with its doc, type/function counts, and the in-module packages it depends on (a call-derived package dependency graph).
• External package dependencies per package.

Metrics

• Total functions and internal/external call counts.
• Average fan-out, most-called function (max fan-in), highest fan-out.
• Longest call chain (cycle-guarded) and high-coupling functions.

Output control for context windows

• --detail low|medium|high selects how much to emit.
• --max-tokens N caps the estimated size; the least important sections are dropped first and the API surface is truncated by call-graph centrality (types and exported functions kept first), with a note of what was omitted.

Flags

Flag	Default	Description
--output, -o	stdout	Write output to a file
--format	markdown	Output format: markdown or json
--detail	high	low (API only), medium (+call graph, metrics, architecture), high (everything)
--max-tokens	0	Cap estimated output size in tokens (0 = unlimited)
--no-structure	false	Omit the file tree
--include-tests	false	Include _test.go files
--exclude-generated	false	Skip Go files marked as generated
--no-progress	false	Disable the stderr progress bar/spinner (auto-off when stderr isn't a terminal)
--verbose, -v	false	Log call-graph build phase timings and per-package counts to stderr
--vv	false	Very verbose: also trace the go/packages driver (go list) invocations and timing

Debugging a slow build

The call-graph step type-checks the whole dependency tree, so on a large repo it can dominate runtime. Use -v to see where the time goes — package load time and the total number of packages type-checked (including transitive dependencies):

witc: loading packages from /path/to/repo ...
witc: loaded 6 module package(s), 172 total incl. dependencies, in 346ms
witc:   walked .../internal/formatter: 4 file(s), +75 edge(s), +42 func node(s) in 0s
witc: built call graph: 92 func node(s), 142 edge(s), 334 external call(s) in 0s

For the most granular view, --vv additionally traces every underlying go list invocation with its individual timing, so you can see which driver call is slow.

Output sections

Markdown output (at --detail high) contains, in order:

1. Structure — file tree (unless --no-structure)
2. Architecture — entry points and the package dependency overview
3. Packages — API surface with docs and inline calls
4. Call Graph — function relationships, entry points, leaf functions
5. Metrics — counts, fan-in/out, coupling
6. Call Flow Summary / Execution Flow — natural-language traces
7. Package Dependencies — external packages used per package

The JSON format emits the same information under a documented, versioned schema — see docs/json-schema.md.

Installation

go install github.com/jomolungmah/witc/cmd/witc@latest

Skill

This repository ships a skill for coding agents at .opencode/skill/witc/SKILL.md (opencode). It tells an agent to run witc summarize to orient itself in an unfamiliar Go codebase before reading or editing.