interface-matrix

An Agent Skill for Claude Code, Codex, Cursor and any harness that reads skills/ from disk: it builds an N² interface matrix — a design structure matrix (DSM) — from a Markdown component and interface inventory, and runs the interface-management gap analysis a sparse interface list hides.

What it does

The input is one Markdown file with a Components table and an Interfaces table, written by you or by an agent from a transcript, spec or code read. Each interface row names a producer, a consumer and four attributes: flows, format, trigger, owner.

The script builds the directed graph of the stated interfaces, partitions it (strongly connected components, then a topological order of the condensation) and reports what the list does not say out loud: interface rows with missing attributes, rows whose producer or consumer is still ?, internal components nothing feeds, outputs nothing consumes, isolated components, feedback loops, and every ordered component pair nobody has stated either way. With --source FILE it also reports the lines of the source document that no cell cites.

The output is one Markdown report on stdout: numbered sections plus the matrix itself, row feeds column. Nothing is inferred and no gap is filled in for you — a gap stays a gap until a human resolves it.

Who it is for

Systems engineers, architects and technical leads planning or auditing a system of roughly eight or more components, at the point where the components are known and the work packages have not been cut yet. It is also pass 3 of the seven-pass decomposition pipeline shipped by macblackstuff/system-adoption-pipeline, and it works on its own.

Example

From skills/interface-matrix, write this to example.md:

## Components

| Component | Kind | Notes |
|---|---|---|
| Ingest |  | pulls raw events |
| Store |  | event store |
| Scorer |  | scores events |
| Analyst | external | reads the digest |

## Interfaces

| Producer | Consumer | Flows | Format | Trigger | Owner | Source | Status |
|---|---|---|---|---|---|---|---|
| Ingest | Store | raw event rows | ndjson file | nightly cron | platform | S:L42 |  |
| Store | Scorer | event batches | ? | ? | platform | S:L44 |  |
| ? | Analyst | weekly digest | ? | ? | ? |  |  |

Then run scripts/interface_matrix.py:

python3 scripts/interface_matrix.py example.md

Eight sections come back. The summary, the two finding tables and the matrix:

## 1. Summary

- components: 4 (3 internal, 1 external)
- specified interfaces: 1
- interfaces with gaps: 1
- explicit none: 0
- missing-component candidates: 1
- unstated pairs: 10
- feedback loops: 0
- self-dependencies: 0
- superseded rows: 0 (interfaces 0, components 0)

## 2. Missing-component candidates

| line | producer | consumer | flows |
|---|---|---|---|
| line 16 | ? | Analyst | weekly digest |

## 3. Interface gaps

| line | producer | consumer | missing |
|---|---|---|---|
| line 15 | Store | Scorer | Format, Trigger |

## 8. Matrix

Row feeds column. Legend: `X` specified, `g` gap, `-` none, blank unstated, `S` self.

           1  2  3  4  
  1 Ingest  .     X    
  2 Analyst    .       
  3 Store         .  g 
  4 Scorer           . 

Three stated rows, and the report names one unowned digest producer, one interface missing its format and trigger, a component nothing feeds, an output nothing consumes, and ten component pairs nobody has ruled in or out.

Install

Harness	Command	Notes
skills CLI	npx skills add macblackstuff/interface-matrix	Pick agents and scope interactively.
Claude Code	npx skills add macblackstuff/interface-matrix --skill interface-matrix -g -a claude-code -y --copy	Verified in CI.
Codex	npx skills add macblackstuff/interface-matrix --skill interface-matrix -g -a codex -y --copy	Verified in CI.
Cursor	npx skills add macblackstuff/interface-matrix --skill interface-matrix -g -a cursor -y --copy	Verified in CI.
Gemini CLI	npx skills add macblackstuff/interface-matrix --skill interface-matrix -g -a gemini-cli -y --copy	Verified in CI.
GitHub Copilot	npx skills add macblackstuff/interface-matrix --skill interface-matrix -g -a github-copilot -y --copy	Verified in CI.
opencode	npx skills add macblackstuff/interface-matrix --skill interface-matrix -g -a opencode -y --copy	Verified in CI.
Any harness that reads skills/ from disk	cp -R skills/interface-matrix /path/to/your/skills/	Every path inside the skill is relative to its own folder, so the destination does not matter.

Verify the install from inside the installed folder with scripts/test_interface_matrix.py:

python3 scripts/test_interface_matrix.py    # Ran 83 tests ... OK

Harnesses tested

CI installs the skill with the skills CLI on every push and pull request, once per agent with --copy, and runs the 83 tests from each installed copy. Six agents are covered: claude-code, codex, cursor, gemini-cli, github-copilot and opencode. Five of the six share one user-level skills directory (the skills CLI decides the target; see its documentation for each agent's path), so on a real machine a single installed copy can serve all five. CI still installs and tests each agent separately, in its own throwaway home, so a change to any one agent's target is caught.

The skill itself is harness-neutral: it is a SKILL.md plus standard-library Python, with no agent-specific commands.

Usage

Ask the agent in natural language — the skill's description triggers on planning or auditing a system of roughly eight or more components, and on any request for an N² diagram, a design structure matrix, an interface list, or a gap analysis between components.

Directly from a shell, run from the skill's own directory:

python3 scripts/interface_matrix.py INPUT.md > OUTPUT.md
python3 scripts/interface_matrix.py INPUT.md --sample 0
python3 scripts/interface_matrix.py INPUT.md --source TRANSCRIPT.txt

--sample N sets how many unstated pairs are printed (default 20, 0 = all). --source FILE adds the coverage section over the document the inventory was read from.

How it works

1. Read the input file: the Components table, the Interfaces table and the optional Rules table; everything else is ignored.
2. Classify each interface row: specified, gap, explicit none, missing-component candidate, or superseded.
3. Apply the Rules table, if present, to settle unstated pairs by producer and consumer class.
4. Build the directed graph and partition it into strongly connected components, then a topological order of the condensation.
5. Report the findings: candidates, gaps, boundary checks, feedback loops, partitioned order, unstated pairs, the matrix, the rules audit, and source coverage under --source.

The procedure an agent follows, including the mandatory human review and how to resolve each finding class, is skills/interface-matrix/SKILL.md. Operating it — health checks, every error message and its fix, rollback and escalation — is skills/interface-matrix/references/RUNBOOK.md.

Output format

One Markdown report on stdout.

Section	Contents
1. Summary	Counts: components, specified interfaces, gaps, explicit none, candidates, unstated pairs, loops, self-dependencies, superseded rows.
2. Missing-component candidates	Rows whose producer or consumer is ?.
3. Interface gaps	Rows missing flows, format, trigger or owner, and which.
4. Boundary check	Internal components nothing feeds, outputs nothing consumes, isolated components.
5. Feedback loops	Loop blocks and self-dependencies.
6. Partitioned order	Components in dependency order.
7. Unstated pairs	Ordered pairs stated neither way, sampled per --sample.
8. Matrix	The N² matrix in partitioned order.
9. Class rules	Per rule: pairs settled and matched, dead rules, unclassed components, residue. Only when a Rules table is present.
10. Source coverage	Uncited spans of the source document. Only under --source.

Requirements and limits

Python 3.9 or newer. Standard library only — no dependencies, no virtualenv, no install step. No network access: the script reads the files you name and writes to stdout.

The matrix is N², so the unstated-pair list grows quadratically with the component count; that is why --sample exists. The script never invents a value to close a gap, never breaks a feedback loop, and does not read your source document unless you pass --source. Its findings are only as good as the inventory you write, which is why SKILL.md makes cell-by-cell human review mandatory rather than optional.

Related

• macblackstuff/system-adoption-pipeline — the seven-pass decomposition pipeline this skill is pass 3 of.
• Agent Skills specification — the SKILL.md format this repo implements.

Contributing, security, license

• CONTRIBUTING.md — how to propose a change.
• CODE_OF_CONDUCT.md — Contributor Covenant 2.1.
• SECURITY.md — supported version and private vulnerability reporting.
• LICENSE — MIT. Copyright (c) 2026 macblackstuff.