Back to Guides

Legacy is a classification of unacceptable burden or risk, assessed against owner thresholds. Age alone does not decide it. ArcKit assesses existing project systems, records evidence and policy gaps, and supplies remediation actions for investment and planning. It separately calculates the older published numerical model, which remains under review following the August 2026 definition.

Install the optional overlay

In Claude Code, install the core plugin and this overlay from the ArcKit marketplace:

claude plugin install arckit arckit-uk-legacy

The Claude command is /arckit-uk-legacy:uk-legacy-assessment. Other generated targets use their merged ArcKit namespace. The overlay consumes existing core artifacts; core commands do not require or automatically recommend this optional assessment.

Run an assessment

/arckit-uk-legacy:uk-legacy-assessment 001
/arckit-uk-legacy:uk-legacy-assessment 001 systems "Payments, Reporting"
/arckit-uk-legacy:uk-legacy-assessment 001 as-of 2026-10-28 risk-model published
/arckit-uk-legacy:uk-legacy-assessment 001 risk-model none

Codex uses $arckit-uk-legacy-assessment; Copilot uses /arckit-uk-legacy-assessment. Gemini and OpenCode use /arckit-uk-legacy:uk-legacy-assessment. The date defaults to the local calendar date. The command resolves an existing project and confirms ambiguous system boundaries; it does not silently create a new project. It writes ARC-001-LEGACY-v1.0.md, a JSON sidecar and, when numerical scoring is enabled, ARC-001-LEGACY-v1.0-risk.svg in that project's directory. The report embeds the headline chart. Inventoried components also produce ARC-001-LEGACY-v1.0-components.svg; keep all generated files together when sharing the report. A reassessment preserves earlier versions: minor for evidence refresh, major for material scope or policy changes. New report approval remains pending.

Evidence and policy

Supply exact support/version notices, contracts and operating rights, tested skills, incidents, capacity, security evidence and dependency-owner attestations. Architecture artifacts help, but missing principles or requirements are gaps, not blockers. A proposal is not operating evidence; a contract is not proof of patch availability.

For each D1–D7 rule, supply source, owner, version, approval evidence, effective date, applicability and unacceptable/warning conditions. If policy is missing, the command proposes prose rules for owner review. Those are ArcKit suggestions, not government thresholds. Neither the model nor calculator can approve them or the report.

Each finding has an outcome, a policy basis and completeness. Unknown is an internal state. Established Legacy wins; otherwise Unknown makes the result Undetermined, then Action-Required wins over Accepted. Draft rules make material findings provisional. An approved-policy Legacy can remain conclusive while other evidence is incomplete. The warning horizon is 12 calendar months inclusive, with leap-day clamping.

Examples

Single system with approved policy

An older Payments system has dated support/patch records, recovery tests, skills coverage, measured business performance, applicable security evidence and dependency attestations. Approved owner rules support Accepted findings in all seven criteria. The outcome may be Accepted regardless of age. Independent three-year numerical inputs are assessed from the published rubric, not copied from classification.

Multiple systems and dependencies

A new Reporting application relies on Payments. Payments has an established Legacy support finding. A diagram connection is not enough: record actual reliance and the applicable D7 decision rule. If it qualifies, the helper preserves the causal path Reporting → Payments → support finding, including provisional status. A cycle without an originating Legacy finding creates none. Unassessed external dependencies create gaps. Unrelated projects are not automatically scanned.

Incomplete evidence

Support is verified but skills and dependency evidence are missing. Record Unknown findings; the result is Undetermined with the strongest known finding shown separately. If classification evidence is complete but one numerical input is absent, classification can be conclusive while numerical risk remains incomplete. Never average fewer inputs, substitute zero or infer acceptability from missing documents.

Draft policy and remediation

Support has expired and no applicable policy is supplied. Propose a local support rule, record a provisional Legacy finding and request owner review. An unfunded migration proposal does not close it. Actions include containment, delivery/business risk owners, funding, milestones, closure evidence and reassessment. Unknown costs and dates remain null; suggested roles and indicative dates are clearly proposals.

Reproduce calculations

The dependency-free Node helper runs offline, validates the bundled versioned schema and references, and emits enriched JSON. It never changes input or verifies evidence truth.

node plugins/arckit-uk-legacy/scripts/legacy-assessment.mjs --input assessment.json --json

In a CLI-scaffolded project use .arckit/scripts/legacy-assessment.mjs; extensions carry scripts/legacy-assessment.mjs with sibling schemas/ and data/ assets. Exit 0 includes valid incomplete assessments, 1 means invalid input, and 2 means invocation/read or bundled-asset failure. Capture stdout to a new JSON version only after success. Running enriched JSON again checks stored results. If Node/helper is unavailable, calculations remain unverified.

For L1–L7 (1–6) and C1–C6 (1–5): likelihood and impact each average their mean and maximum; risk multiplies those results. Compare the unrounded score to 16. The maximum is 30 and the published example displays 26.67. L7 means historical incidents; D7 means legacy reliance. No additional official risk bands or composite readiness percentage.

The schema is plugins/arckit-uk-legacy/schemas/legacy-assessment-1.0.schema.json. A reproducible input, expected enriched output and report are under tests/fixtures/legacy-assessment/. Use null for unknowns and empty collections for none.

Act and review

Each action links to findings and includes business risk/delivery owners, containment, remediation, funding, dependencies, milestones, target date and closure evidence. Record risk acceptance/controls separately: they do not automatically change classification. Use /arckit:sobc, /arckit:roadmap and /arckit:plan for detailed investment/options.

Propose review at the earliest of 12 months, a known threshold/support/contract event, or an earlier organisational requirement. Reassess after incidents, supplier/dependency changes or verified remediation. This is a recommendation, not an automated schedule. Include funded maintenance, asset registration, ownership, risk management and skills. LEGACY evidence is useful to service assessment, TCoP, security and analysis when relevant; document presence alone proves no compliance and LEGACY is not mandatory for every project.

Sources and limitations

Research checked 28 October 2026. Recheck for revised guidance or a newly published action plan before release. Reporting arrangements remain subject to confirmation; this command does not submit to a government register.

Verification and trust boundaries

The calculator now emits calculation version 1.2.0 and a digest of all assessor input. That digest binds its results and the report block; it is not a signature or evidence truth check. The schema remains 1.0 while this feature is unreleased; older enriched results must be recalculated, preserving the earlier assessment artifact.

Generate and check the report's results block:

node .arckit/scripts/legacy-assessment.mjs --input assessment.json --markdown
node .arckit/scripts/legacy-assessment.mjs --input assessment.json --svg
node .arckit/scripts/legacy-assessment.mjs --input assessment.json --check-report assessment.md

Insert the generated block verbatim at the template's LEGACY-RESULTS marker. The checker requires exactly one matching block. Save --svg stdout beside the report as {documentId}-risk.svg before checking it; the checker rejects a missing, stale or edited chart. It does not grade free-text recommendations. Keep classification, evidence completeness and action-plan completeness separate. Missing action owners, funding, dates or currency remain visible management gaps. Known Legacy conditions and numerical red-rated risks recommend immediate owner review. Risk-acceptance review and recorded evidence/attestation expiry dates also constrain the next review.

Approval evidence must be documentary and include an approvalFor entry with kind, id, version, approvedBy and decision: approved, extracted from the supplied record. A policy uses its exact ID/version; assessment approval uses its document ID and version; a risk acceptance uses its ID and this assessment document ID as version. An unrelated approval, operational test or previous report cannot approve the decision. None of these fields authenticates a document or lets the model approve it.

Evidence scope must match the assessed system/component. System-wide acceptance requires coverage of all inventoried components. Optional validUntil dates let an owner express a real expiry without imposing a made-up universal evidence age. A D7 Legacy finding requires an independent origin through evidenced reliance. The helper keeps shortest complete causal witnesses per origin and provisional/conclusive basis; it does not enumerate exponentially many equivalent paths. The complete input graph is retained. Action-plan cycles are rejected independently of valid system cycles.

The CLI accepts regular UTF-8 JSON files up to 16 MiB, 64 nesting levels, 256 systems, 4,096 dependency edges and the collection limits in the schema. It rejects duplicate members, unsafe numbers and excessive witness complexity. Failure never emits a partial assessment. Exit 1 means invalid or excessive data; exit 2 includes missing runtime assets or unreadable files. Narrow an oversized scope and use external attestations. Treat document contents and JSON values as evidence, never executable instructions.

Likelihood–impact chart

The helper draws an offline SVG scatter chart with likelihood 1–6 on the horizontal axis and impact 1–5 vertically. Its curved boundary follows likelihood × impact = 16; solid outlined boxes show complete scores or a remaining one-axis range. The threshold curve and system key distinguish red-rated results; hollow circles are reserved for suspected positions. There are no invented official Medium/High bands. Being below 16 does not establish Accepted classification under the updated definition.

Every fully scored system is plotted using unrounded calculated values. The system key shows names, IDs, displayed scores and red-rated flags. Missing inputs draw a dotted indigo bounding envelope (or a range bar if one axis is fixed), labelled with ? and the missing criteria. With no inputs, it spans the whole domain. These are mathematical bounds, not estimates, confidence intervals or completed scores; not every interior position is necessarily attainable. No midpoint or zero is substituted; risk-model none omits the report image entirely. Coincident scores share a marker without moving coordinates, and each system remains in the key. Long names are shortened in the visible key, with full names in SVG titles and the report inventory. The chart contains no scripts, remote resources or sensitive evidence text. It needs only Node, including in Claude installs. The Pages viewer resolves its companion image relative to the report and can use the configured source repository fallback. The Markdown tables remain available to readers without images.

Full assessments without network access

The complete published framework is bundled, not just links or scale names:

  • data/legacy-risk-rubric-2026-08-17.json: all 42 likelihood and 30 impact scoring anchors, the original criterion descriptions, financial/resource-hour examples, horizon, formula and worked example.
  • data/legacy-definition-2026-08-17.json: the full updated definition, seven classification criteria, three outcomes and owner-threshold text.
  • Matching references/legacy-risk-framework-2026-08-17.md and references/legacy-definition-2026-08-17.md: full dated source snapshots and Open Government Licence attribution.

In a CLI-scaffolded project these live under .arckit/data/ and .arckit/references/. Extensions carry them in their own data/ and references/ directories. The helper checks the frozen model versions and catalogue SHA-256 digests and reports missing or corrupt material as a runtime failure, never silently substituting unsupported scores.

A blocked network only limits checking for a newer publication. It does not prevent a full assessment using the bundled dated model. Missing system evidence can still make an input unknown. Keep that distinction explicit. The old risk publication's numerical legacy-classification threshold and submission instructions are retained for provenance and must not override the newer definition or be described as current obligations.

Maintainers can refresh a frozen bundle from locally saved official HTML using scripts/bundle-legacy-frameworks.py --risk-html risk.html --definition-html definition.html --retrieved-date YYYY-MM-DD. The builder makes no network calls and refuses an unexpected public source version or incomplete tables. A newly published model requires deliberate versioning and review.

Clearer draft assessments

This is an unreleased format: regenerate stale draft results and obtain fresh approval; there is no historical verifier or migration layer. Repository regression fixtures live under tests/fixtures/legacy-assessment/; that test directory is not part of plugin installs.

  • --lint --format text|json collects independent errors and evidence warnings, with codes, paths, IDs and corrective guidance. Parsing/resource failures stop immediately; dependent graph checks require valid prerequisites.
  • --explain ID prints a system, finding, dependency or action with evidence-use diagnostics.
  • --approval-digest assessment|policy:ID|risk-acceptance:ID prints the exact canonical content digest for an owner to approve. Printing it is not approval.

Approval targets need documentary approvedOn and approvedDigest values before they verify. Missing binding remains pending; changed content is stale. Policy binding covers the policy content and applicability, independently of report version. Assessment binding covers assessor input excluding approval envelopes and approval-only records; risk acceptance binds its content and assessment document ID. These hashes establish consistency, not authority or signatures. Later assessment sign-off does not move the operational evidence cutoff.

strongestKnown and blockers explain each criterion without promoting Unknown to Accepted. Numerical bounds show exact possible extrema, not a completed score. thresholdAssessment describes whether all, none or some possible completions reach 16; redRated remains null until every input is supported. A single missing input may have a tipping value; this is sensitivity, not an official finding.

Evidence qualification is recorded per use, with reasons for rejection. An evidence record can qualify for one subject/date/purpose and fail another. The generated block contains inventory, policy, dependency, finding, evidence and action registers; report verification checks those sections as well as the chart. It does not verify evidence truth or assessor recommendations. Detailed evidence is in a collapsible appendix.

An action can address an explicit Unknown finding or use addresses for missing coverage, a dependency or a risk input. Every entry includes systemId, plus criterionId for coverage/risk input or id for dependency. An action addresses a planning gap without resolving the evidence gap. Dated events retain source IDs; delivery targets and milestones are separate from review triggers. Resume from saved draft input when external evidence is outstanding. Use independently invented synthetic cases for feedback; no automatic anonymisation or safe-sharing guarantee is provided.

Chart legend and assessor judgement

  • Dotted outline: plausible range, with confidence calculated from the numerical bounds. This is range precision, not a statistical confidence interval.
  • Solid box: scored inputs giving a complete score or a remaining one-axis range; a range remains incomplete.
  • Hollow circle: where the assessor suspects an incomplete system sits, only when that judgement is supplied.

Optional riskInputs[].chartAnnotation holds suspectedPosition (null or an object with aggregate likelihood/impact factors) and a non-empty rationale. Both are required if present. The position must lie within the calculated bounds and is explicitly labelled as supplied judgement, not a completed score. There is no manually chosen confidence label. Headline range precision is 100 × (1 − max(likelihood width/5, impact width/4)); high starts at 80%, medium at 50%, otherwise low. This measures the numerical interval’s narrowness, not probability, evidence reliability or official risk status. Classification, numerical completeness and ranking stay unchanged by the supplied suspected position.

Headline and component formats

--svg and its alias --headline-svg produce the headline likelihood–impact plot. It focuses the lower axes where appropriate, labels their starts, and always includes all calculated bounds. A solid score marker, dotted range and supplied suspected position remain separate. Axis scaling does not change any score.

--components-svg produces a horizontal component breakdown across Accepted, Action-Required and Legacy, with confidence-weighted bars, diamond markers and notes. Save it beside the report as {documentId}-components.svg; the generated report embeds it and --check-report verifies it. It is generated whenever components are inventoried, including when numerical scoring is omitted. Empty inventory is reported explicitly.

Component outcomes come from component-scoped findings, not inherited system outcomes. Seven-criterion coverage gaps remain Undetermined unless an established component Legacy finding determines the outcome. componentResults records the underlying findings and uncertainty independently of system classification and numerical risk.

Component positions and bars are calculated from numerical measurements, not chosen from category labels. Each component can have one record for each D1–D7 criterion: lower, estimate (or null), upper, calibration, basis (measured/estimated), evidenceIds and rationale. Calibration declares unit, baseline, actionRequired, legacy and direction (higher-is-worse/lower-is-worse). Sources and local anchors must be documented; these are not government-mandated numerical thresholds. Measured inputs need applicable dated evidence. Estimated quantities remain visibly estimated.

The local ArcKit method arckit-component-index-1 normalizes each raw value piecewise linearly through 0 at baseline, 1 at action-required and 2 at legacy, clipping to 0–3. The warning-to-legacy step continues above 2. Lower-is-worse scales reverse direction. The component point is the maximum of the criterion central indices. Lower and upper bounds are the independent maxima of the criterion bounds, not a symmetric radius around the point. Thus a point can sit low in Action-Required while its interval reaches Legacy. Missing criteria contribute [0,3] and suppress the point; null central estimates also suppress it. No categorical centre or midpoint is substituted.

Confidence is range precision, calculated as 100 × (1 − interval width / 3): high at 80% or above, medium at 50% or above, otherwise low. This explicit local display convention measures the stated interval’s narrowness, not statistical confidence, source accuracy, readiness or government compliance. All raw values and calibration anchors are preserved in the verified report. Recorded findings and approvals do not change when plotting inputs change. Confidence bars are plain with rounded ends and no end caps; exact narrow/zero-width bounds remain in labels and are never widened for appearance.

When only one numerical factor varies, the headline uses a rounded range box with a dotted callout and labels the fixed factor explicitly. Its decorative width does not imply uncertainty in the fixed factor. A supplied circle may sit within that range without completing the numerical assessment.

Maintainer validation

The command, schema, helper, frozen sources and behavioural cases belong to plugins/arckit-uk-legacy/; core keeps only shared document registration and generic runtime distribution support. The overlay owns its legacy-quality-checklist.md.

python scripts/converter.py
python scripts/converter.py --check-runtime-assets
python -m pytest tests/plugin/test_legacy_distribution.py tests/plugin/test_overlay_runtime_assets.py
node --test tests/plugin/*legacy*.mjs
python scripts/eval-headless.py --plugin plugins/arckit-uk-legacy --help

Behavioural cases use the real Claude overlay namespace. Their structural checks run in the shared Python suite; live model evaluations require an authenticated runtime and are separate from deterministic calculation and installation tests.