What is mantis-structural-index?

A source-code index that maps meaningful code units and their relationships, such as which functions call another function. It stores this information so an agent can look up code structure while studying a pinned or live codebase.

Use it before architecture summaries or other discovery work on a repository. It helps locate callers of a symbol, identify where a function starts and ends, and understand call sites.

It reduces the need to rediscover callers and function boundaries by searching through files repeatedly. This gives code research better structural context without replacing normal text search.

mantis-structural-index — Skill by google

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add skills/google/mantis/mantis-structural-index

Any agent

npx skills add google/mantis --skill mantis-structural-index

Clone the repo

git clone --depth 1 https://github.com/google/mantis

Made for: Claude Code, Codex.

Per session 55 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 8,881 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5	$0.00055	$0.08881
Opus 5	$0.00028	$0.04441
Sonnet 5	$0.00011	$0.01776
Haiku 4.5	$0.00006	$0.00888

Measured 2d ago against content hash 5a65e5589084, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

mantis-structural-index scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

mantis-structural-index/SKILL.md · 747 lines

How it starts

The opening of the file, as written. The whole thing — 747 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Structural Code Index Builder

This is an optional first-class stage in the Pass Lifecycle Contract. It runs immediately after the snapshot is pinned (Block D), before the first code-reading analysis stage (summarize/architecture). It only needs CODE_ROOT + SNAPSHOT_ID and must not depend on architecture/KB.

System Goal

Structural Code Index Builder. Builds a content-addressed semantic-unit index from source code using capability-based per-partition backend selection, degrading gracefully to grep. Provides find_callers(symbol), get_function_boundary(file, line), and call-site awareness to improve LLM reasoning quality during discovery — supplementing (never replacing) grep-based call-site discovery with structural data. The index is composed from independent semantic compilation units, persisted as a manifest + SQLite catalog, and exposed through a bounded query helper.

Command Definition

Command: /mantis-structural-index
Description: Build a content-addressed semantic-unit index from source code under CODE_ROOT.
Arguments (optional; supplied by the orchestrator, consumed by Block A): --snapshot_root/--snapshot_id/--state_root. All absent → MODE-OFF/legacy mode (reads source from the current directory, writes index to ./workspace/kb/structural_index/).

Input/Output Contract

Reads:
- workspace/.mantis_state.json (to read active_snapshot for provenance checking and snapshot-aware rebuild logic).
- workspace/kb/structural_index/manifest.json (to check snapshot_id for reuse-on-match idempotency — primary check).
- workspace/kb/structural_index.jsonl (backward-compat provenance check if manifest absent).
- workspace/kb/structural_index/units/ (content-addressed cache for incremental unit reuse).
- workspace/kb/structural_index/native/ and sidecar provenance.json files (prebuilt index attachments and metadata manifests).
- CODE_ROOT source files (via generated helper script — the script parses all source files under CODE_ROOT).
Writes:
- workspace/kb/structural_index/manifest.json (STATE-RELATIVE — atomic commit point, written LAST).
- workspace/kb/structural_index/catalog.sqlite (STATE-RELATIVE — query-optimized serving store).
- workspace/kb/structural_index/units/ (STATE-RELATIVE — content-addressed immutable unit outputs).
- workspace/kb/structural_index/shards/ (STATE-RELATIVE — partitioned serving data for large corpora).
- workspace/kb/structural_index/native/ (STATE-RELATIVE — prebuilt index attachments: SCIP, Kythe, LSIF).
- workspace/kb/structural_index/tmp/ (STATE-RELATIVE — temporary objects during build).
- workspace/kb/structural_index.jsonl (STATE-RELATIVE — compatibility pointer; full export below threshold).
- workspace/helpers/build_structural_index.py (STATE-RELATIVE — the builder helper script).
- workspace/helpers/query_structural_index.py (STATE-RELATIVE — the query helper script).
Preconditions:
- Source files must exist under CODE_ROOT. If CODE_ROOT is not resolved (MODE-OFF and no readable active_snapshot), build against the current directory with snapshot_id set to "unknown". Do NOT skip — this is the standalone-efficiency case.
Inert until wired: This skill returns an empty index until a caller invokes it (the harness, mantis-plan, or mantis-researcher). It never fails — it simply returns an empty index if tools are unavailable or source cannot be parsed.
Idempotency Guarantee:
- Read-only on CODE_ROOT. Writes only to STATE-RELATIVE paths. Re-running with the same CODE_ROOT and SNAPSHOT_ID reuses the existing index (manifest snapshot_id match) rather than rebuilding — except in MODE-OFF, where it always rebuilds. Individual semantic units are reused across snapshots when their content-addressed cache keys match (incremental rebuild).

Read the full file on GitHub · 747 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2d ago First seen · 747 lines · 55 tokens per session scan A 5a65e5589084

Subscribe to this mod's changes

mantis-structural-index is a skill published in the GitHub repository google/mantis (853 stars, last pushed 5d ago), licensed Apache-2.0. It adds 55 tokens to every session and 8,881 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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mantis-structural-index

Getting it into your agent

What it costs to keep this loaded

Grade A, and why

Nothing flagged

How it starts

Structural Code Index Builder

System Goal

Command Definition

Input/Output Contract

What this file has done since we first saw it

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