skeletongraph

SkeletonGraph

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Coding agents burn tokens reading whole files to find one function. SkeletonGraph indexes your repo with tree-sitter — no LLM — and hands the agent the exact function to edit, over MCP.

Index once (no LLM) → fuse lexical + semantic + structural signals → return the exact function, served to your agent over MCP.

SkeletonGraph is a retrieval engine purpose-built for coding agents, not a general RAG library retrofitted onto code. It parses a repository into function-level structure, a cross-file call graph, and PageRank centrality with zero LLM calls — deterministic, cheap, and instant to rebuild after every edit. At query time it resolves the symbols an issue names, walks the call graph outward, and reranks a BM25 recall pool by structural confirmation so the agent lands on the right function on the first try, instead of grepping and re-reading its way there. Its leaner operating point, sg-rerank (the product default), skips the dense leg entirely and still delivers the best file and function recall of any method we benchmarked it against — at the lowest token cost of any of them.

The thesis: code-context tools have mostly been validated as a token-optimization game — how few tokens can you spend. SkeletonGraph re-centers the question on retrieval quality — did the agent land on the correct function — of which lower token cost turns out to be a consequence, measurable only end-to-end inside a real agent loop, not in an offline benchmark.

Results

All numbers below are regenerated from the released run artifacts (python -m eval.scripts.make_paper_figures). The full verified ledger, including withdrawn claims, is in docs/paper/FINDINGS.md.

1. Controlled retrieval ablation (react loop, open-weight model, 100 tasks)

Identical action space for every arm; only the retrieval backend changes. The none arm gets no code access at all and establishes the memorization floor.

arm	pass@1	file recall@1	function hit	tokens (k)	turns	$/task
sg-fusion	42.0%	.737	57%	180	21.9	.052
bm25	41.0%	.642	43%	264	24.6	.074
graphify (knowledge graph)	41.0%	.223	9%	275	25.6	.078
grep	39.0%	.647	0%	282	22.4	.079
aider (repo-map)	36.7%	—	—	1,126	18.1	.160
none (no retrieval)	35.0%	—	—	345	23.6	.066

sg-fusion is the top arm, the cheapest arm, and the only one that localizes to the function (57% vs grep's 0% — lexical search is file-granular by construction). Against the closed-book floor of 35.0%, retrieval is worth +7 points here.

sg-rerank's recall/cost profile is reported separately in the agent-free intrinsic retrieval ablation in docs/paper/skeletongraph.tex (Table 2, §5.1) — best MRR/recall@10 short of full fusion, at the lowest index cost.

2. Deployment: SkeletonGraph vs native Claude Code (MCP, Docker-verified)

The product itself — SG as an MCP server driving Claude Code (sonnet) against Claude Code on its own tools. 100 paired SWE-bench Verified tasks:

arm	pass@1	file recall@1	turns	$/task
native (Claude's own Grep/Read)	74/100	.663	14.5	.434
sg-fusion (SkeletonGraph MCP)	75/100	.836	11.4	.371

Equivalent solve rate at −14.6% cost and −21.4% turns. The saving is not spread evenly — it lives almost entirely in the tail:

cost percentile	native	+SG	change
50th (median task)	$0.255	$0.260	+1.9%
90th	$1.010	$0.752	−25.6%
95th (worst tasks)	$1.559	$0.896	−42.5%

Retrieval does nothing for the typical task and removes over 40% of the cost of the worst ones. Paired bootstrap 95% CI on the mean: [−25.3%, −1.2%]; McNemar on pass@1: p = 1.0 (no difference).

3. The ceiling: what structural retrieval cannot do

sg-fusion runs all three non-LLM retrieval paradigms at once — lexical (BM25), semantic (code embeddings), and topological (call graph). Crossing memorization (standard vs. decontaminated benchmark) against location cues (original vs. prose-stripped issue text) shows the limit:

condition	cost	file recall native → SG
SWE-Verified, raw	−32.2%	.661 → .861
SWE-Verified, prose-only	−21.1%	.717 → .711 (no edge)
SWE-rebench (unseen repos), raw	−26.4%	.500 → .639
SWE-rebench, prose-only	−31.3%	.394 → .439

Two things happen at once. The retrieval advantage collapses — on prose-only issues it disappears entirely — and the lexical baseline falls in parallel, so this is a property of the whole category, not of one implementation. Yet the cost saving persists in every condition, including the one where retrieval quality is identical to the baseline. Retrieval quality is therefore not the mechanism producing the saving; bounding how far the agent wanders before it commits is.

SWE-Verified rows are restricted to the same 15 tasks as the prose run so raw and prose are paired. That subset is not representative of the full 100 (SG saves −32.2% on it vs −14.6% overall) — do not compare it against the n=100 figure.

4. Deployment finding: slow MCP servers are structurally excluded

Two graph/LSP-based competitors wired as MCP servers never participated at all. Claude Code's headless (-p) mode finalizes its tool manifest within ~2 seconds of launch and never updates it; servers needing real bootstrap time (a language server, a Node CLI + index) finish their handshake just past that window and are silently absent for the entire run — confirmed via session-init transcripts and each server's own logs showing it was ready seconds later.

This is a deployment-mode result, not a retrieval-quality one, and we report no performance comparison for those systems: with zero tool calls, any such number would measure their absence rather than their retrieval. A separately wired zero-LLM graph competitor connected cleanly with all 14 tools visible, yet the agent never invoked one across 10 tasks, defaulting to native grep every time. Fast connection and actual adoption are prerequisites that retrieval quality cannot substitute for.

SkeletonGraph is wrapper-first: it returns a full context packet or exposes a retrieval index (AST skeletons + call graph + local summaries + optional embeddings) so the IDE agent or CLI can choose targets.

SkeletonGraph has two product surfaces:

• SG IDE: MCP context server for Cursor, Claude Code, Copilot, Codex, Antigravity, Windsurf, and other agentic IDEs.
• SG CLI: terminal pipeline for route, prepare, dry-run, provider execution, and cost-aware model selection.

Why SkeletonGraph

Most coding agents spend expensive turns discovering the repo:

search -> read file -> read neighbor -> read tests -> realize the target

SkeletonGraph moves that work into a deterministic graph pipeline:

prompt -> (optional) retrieval planner -> classify task -> find target nodes -> expand graph -> assemble packet

The goal is not only lower token cost. The useful product outcomes are:

• fewer exploratory file reads
• faster first useful answer
• better target/test/blast-radius context
• transparent routing reasons
• lower model overkill for routine tasks
• reusable packets for IDEs, CLIs, and other agents

Install

pip install skeletongraph           # core: indexing, MCP server, CLI (no API key needed)
pip install "skeletongraph[llm]"    # + litellm for sg run --execute / sg summarize --tier cloud
pip install "skeletongraph[all]"    # everything

Quick Start: SG IDE

Use this path when you already work inside Cursor, Claude Code, Copilot, Codex, Antigravity, or another MCP-capable coding environment.

cd your-project
sg init
sg build
sg doctor

sg init writes the MCP config and the agent instruction file for the selected IDE. SG IDE does not require an API key. Your IDE subscription/model still does the reasoning and editing; SkeletonGraph supplies the packet or retrieval signals for efficient target selection.

Supported IDE setup targets include:

IDE	Integration	Model switching
Cursor	MCP + rules	manual in IDE
Claude Code	MCP + CLAUDE.md	/model command
GitHub Copilot	MCP + instructions	manual in IDE
Codex	MCP + AGENTS.md	manual in agent
Antigravity	MCP + rules	manual in IDE
Windsurf	MCP + rules	manual in IDE

Quick Start: SG CLI

Use this path when you want a terminal-first context and model-routing pipeline.

cd your-project
sg build
sg route "fix the auth token validation bug"
sg prepare "fix the auth token validation bug" --out .skeletongraph/context.md
sg run "fix the auth token validation bug" --dry-run

sg route, sg prepare, and sg run --dry-run do not need an API key.

To call a provider:

sg config --cli-provider anthropic
$env:ANTHROPIC_API_KEY = "..."
sg run "fix the auth token validation bug" --execute

To test locally without a paid provider key:

ollama pull qwen3-coder:latest
ollama serve
sg config --cli-provider local
sg run "fix the auth token validation bug" --dry-run
sg run "fix the auth token validation bug" --execute

Local execution is intended for cheap pipeline testing. Use provider models for quality benchmarks unless the benchmark is specifically for local models.

Model Dependency, Prewarming, and Keeping the Index Fresh

SG downloads two small embedding models on first use, both via sentence-transformers (a hard dependency, not optional):

• jinaai/jina-embeddings-v2-base-code (SG_DENSE_MODEL) — the semantic leg of fusion/sg_search. Loaded on sg warm or on an agent's first dense-retrieval query. Loads with trust_remote_code=True (Jina ships custom modeling code on the HF Hub) — this executes code from that model repo, same as any trust_remote_code model.
• all-MiniLM-L6-v2 (SG_EMBED_MODEL) — a smaller, separate model used only as a confidence-score tiebreaker at index time. Downloads automatically on the first sg build, not on sg warm.

Both need internet access the very first time each is used on a machine — after that, both are cached locally (Hugging Face's model cache, plus SG's own content-hash caches: .skeletongraph/dense_cache for the dense leg, .skeletongraph/embeddings.npz for the confidence tiebreaker) — so later builds are incremental: only functions whose text actually changed get re-embedded.

Prewarm before launching an agent, so that cost lands during setup instead of on the agent's first real search:

sg build                 # parse + structural index (no LLM, fast)
sg warm --path .          # prebuild BM25 + dense caches (one-time; minutes on CPU)
sg warm --path . --mode rerank   # skip the dense leg entirely (no embedding cost)

Without this, the first sg_search call an agent makes pays the cold-encode cost inline — on a large repo this can exceed the dense retrieval leg's internal timeout (SG_DENSE_TIMEOUT_S, 20s by default), in which case it silently degrades to a 2-signal (lexical + structural) result rather than failing outright. Prewarming avoids relying on that fallback altogether.

Keeping the index current as files change — two options, pick based on how you work:

sg update --path .        # one-shot: re-index only files that changed since last build
sg watch --path .         # background daemon: auto-reindexes on save (needs `pip install "skeletongraph[daemon]"`)

sg watch is the hands-off option for active development — it debounces rapid saves and calls the same incremental update path as sg update, so editing a file is reflected in the index without a manual rebuild.

Model Routing

SkeletonGraph separates IDE-facing model labels from CLI provider model names.

For IDEs, model tiers are recommendations:

Tier	Typical use
SLM	docs, explanations, simple lookup
MLM	normal coding, debugging, tests, review
LLM	architecture, broad migrations, low-confidence tasks

For CLI execution, SkeletonGraph can route to provider model names:

sg config --cli-provider anthropic
sg config --cli-provider openai
sg config --cli-provider google
sg config --cli-provider local

Dynamic routing uses task mode, confidence, candidate count, token size, and complexity. Code-changing work keeps an MLM floor by default so cost savings do not come from making weak models edit code unsafely. Retrieval planning can use small models to propose targets over AST/summaries before the heavy model runs.

IDE Integration

After sg init and sg build, register SG as an MCP server and write IDE hooks:

sg install --ide claude-code   # Claude Code: hooks + MCP server + CLAUDE.md rules
sg install --ide cursor        # Cursor: MCP + .cursor/rules/skeletongraph.mdc + hooks
sg install --ide cline         # Cline / Roo: MCP config + rules block
sg install --ide copilot       # GitHub Copilot: MCP + copilot-instructions.md
sg install --ide windsurf      # Windsurf: MCP + .windsurfrules
sg install                     # auto-detect all installed IDEs

After install, restart your editor. SkeletonGraph runs as a background MCP server (sg serve --path .) that the IDE connects to automatically.

MCP Tools

Six tools are exposed to the IDE agent. Use these instead of grep/glob/file reads:

Tool	When to call	Returns
sg_overview	Session start — once per session	Constraints + top-N functions (by PageRank) + recent turns + index stats
sg_search "query"	Primary retrieval — almost every prompt	Top-3 matches with body excerpts + summaries + 1-hop callers; top-4..N as signatures + summaries. One call usually enough — no need to chain.
sg_get "fqn"	When the exact FQN is known	Signature + summary + 1-hop callers + callees
sg_expand "target"	When more body is needed than sg_search returned	Full function body / file / line range (token-capped)
sg_constraint list / propose	Before proposing changes	Confirmed + proposed project rules
sg_log	Reviewing recent session turns	Last-N turn summaries with files touched

Smart context routing. On each UserPromptSubmit, SG classifies the prompt (architecture / explain / decision / debug / test / review / general) and includes the matching MD file from .skeletongraph/ — e.g. architecture.md only for design/refactor queries, project.md only for "what is this codebase" queries. Constraints + session digest + relevant functions are always injected.

Cold start. If no .skeletongraph/ index exists when an MCP tool is called, SG auto-builds on first invocation (see auto_build_on_query in config).

CLI Reference

Indexing & status

Command	Purpose
sg init [--agent cursor]	Configure project, IDE preset, MCP, constraints
sg index	Full index (alias for sg build)
sg index --incremental	Only re-index changed files
sg build	Full index with detailed output
sg update	Incremental update
sg status	Show index status
sg doctor	Check index, routing, provider, Ollama readiness
sg overview	Project skeleton: top functions, constraints, session
sg install [--ide <name>]	Write IDE hooks + MCP config

Retrieval

Command	Purpose
sg search "query"	BM25 + graph search (no API key)
sg get "fqn"	Get function signature, summary, callers
sg expand "target"	Expand function body / file / line range

Constraints & session

Command	Purpose
sg constraint list	List all constraints
sg constraint propose "text"	Add a proposal
sg constraint confirm <id>	Promote proposal → decisions.md
sg constraint remove <id>	Remove a constraint
sg constraint aggregate	Import from IDE rule files
sg log [--last-n 10]	Show recent session turns

Summarization

Command	Purpose	API key
sg summarize --tier local	Ollama Tier-0.5 (free, on-device)	no
sg summarize --tier cloud	Cloud LLM Tier-1	provider key
sg summarize --tier cloud --force	Re-summarize all functions	provider key

Model routing & execution

Command	Purpose	API key
sg route "task"	Show task mode, tier, recommended model	no
sg run "task" --dry-run	Plan routed execution	no
sg run "task" --execute	Call configured provider	provider or local
sg config [--agent cursor]	Configure IDE and CLI models	no
sg config --cli-provider anthropic	Set CLI execution provider	no

Background indexing

Command	Purpose
sg watch	Daemon: auto-reindex files on save

Provider output from sg run --execute is written to .skeletongraph/runs/. Evaluation is currently done externally via SWE-bench harness — see docs/swe_bench_runbook.md.

Python API

from skeletongraph.engine import SGEngine

engine = SGEngine(project_root=".")
result = engine.query("fix the content-length bug", delivery="cli")

print(result.context_text)
print(result.query_mode)
print(result.model_tier)
print(result.recommended_model)
print(result.routing_reason)

Architecture

src/skeletongraph/
  parser/       AST extraction
  graph/        dependency graph and ranking
  storage/      .skeletongraph persistence
  retrieval/    classification, resolution, model routing
  assembly/     context packet construction
  session/      memory and dedup
  server/       MCP server
  llm/          LiteLLM wrapper for optional CLI execution
  cli/          Click commands
  engine.py     unified query pipeline

Evaluation

The architecture/pipeline blueprint and evaluation plan are in:

docs/blueprint.md
docs/evaluation.md

SkeletonGraph should be evaluated on both quality and cost:

• target recall and packet completeness
• missed tests/callers
• first useful answer latency
• file reads after SG context
• pass rate
• cost per passing task
• dynamic routing overkill/underpower rate
• IDE compliance with SG-first context usage

Cost savings are only meaningful when reported with pass rate.

License

MIT