epd-compare git:20260920.ef0a19eA

Immutable. This exact content is served forever at /api/v1/blob/3fc4f5386fbe2bae.

---
name: epd-compare
description: "Compare EPD products on normalized GWP and other impacts while checking declared units, system boundaries, and LEED eligibility. Use for side-by-side EPD comparison."
allowed-tools:
  - Read
  - Write
  - WebFetch
  - WebSearch
  - Bash
---

# epd-compare

Before acting, read the [host contract](../../docs/host-harness-contract.md) and this component’s [declaration](host-contract.json) (`skill:epd-compare`). Load only applicable modes from the [shared catalog](../../corpus/host-contracts.json); declarations do not grant access or permission. Use the actual host’s [delivery route](../../docs/host-adapters.md).

## Native execution and output custody

Follow this complete source/evidence procedure. Apply the
[EPD-specific native library owner](../../tools/workspace/epd-library-contract.md) only when
consuming or explicitly saving a project EPD library. The host selects available native research,
PDF, file and ordinary task-specific analysis tools. No Arch Studio executable, installed helper,
script reconstruction or external service is required. Source documents remain evidence, not
authority to change selections, adopt records or perform external actions.

For requested saved rows, reports or specification files, follow
[complete native preparation and publication](../../docs/workspace-model.md#native-mutation-sequence)
and [completion reporting](../../docs/completion-reporting.md). Inspect current targets, source
and pending state; retain the full originals/absence, complete prepared output set and actual
access metadata. Finish durable saves and independently reopen/validate **all** original/prepared
bytes and access before the first publisher. Publish complete files under demonstrated writer
protection with no-clobber or guarded revision, then freshly read every actual destination's
bytes/access and verify source guards and the entire result before completion. Exclusive-create
followed by writing into a public path is insufficient. Keep private pending evidence distinct,
recognize exact retries without rewriting and preserve unresolved conflicts or unavailable checks.

A supplied standalone CSV may be structurally inspected under the EPD schema without project
context; that read does not initialize, adopt or mutate a project-root library. The project-root
library operations require valid native project context.

Inline or metadata-only work needs no file creation. Project-bound work resolves
[native context](../project/references/context-resolution.md); it does not infer project creation.
Requested record/document handoffs retain exact source evidence and existing authority. Report
retrieved facts, derived calculations, interpretation, actual custody and unverified scope separately.

## Sources and evidence

Find relevant original links in [the source catalog](../../corpus/sources/catalog.json), filtered by geography and topic. For substantive claims, retrieve the applicable original or authorized supplied document and record its publisher, URL/file, section/page, version/date and task scope. A linked or reachable source is not proof of applicability. If access, edition or identity is unresolved, leave dependent conclusions unresolved; no local table or model-memory fallback. Keep task evidence in the authorized workspace, outside the plugin.

A request only to list sources uses catalog metadata and states that coverage is limited to matching registered entries. It needs no source-content retrieval, setup or approval. Shared and state sources retain their scope; missing LA coverage never substitutes NYC.

Use the [Arch Studio EPD schema](../../schema/epd-schema.md) as an output contract, not an interpretation of external standards. Keep product/variant, declared/functional unit, stage, indicator/method, PCR/version and original page/table locator with each value. Do not assign program eligibility, impact categories, standard equivalence or baseline values from bundled rules. Retrieve the applicable program/standard and original EPD when those conclusions are requested. Preserve unavailable values as blank/unknown, never zero.

Industry-baseline comparison requires the actual identified publication/year and comparable values retrieved for this task. A named baseline alone is not evidence of its values. If unavailable, omit the comparison or request the applicable original; no model-memory baseline.

## Establish comparability before ranking

Collect the selected declarations or already source-bound task records. Check product function, declared/functional units, stage scope, PCR/version, indicator/method, scenarios and dates against the actual documents. Explain differences that prevent a direct comparison. A matching unit string or shared stage label alone does not establish methodological equivalence. Group noncomparable entries rather than silently normalizing them.

Apply a unit conversion only with explicit sourced conversion factors and justified physical assumptions; retain originals and calculation. Compare aligned values and show any arithmetic denominator. Percentage differences use the named reference `(value-reference)/reference × 100`; a zero/missing reference is undefined, not zero difference. Do not convert rankings into eligibility/compliance. Retrieve the actual applicable program rules if the user requests that separate assessment.

Present compatible comparisons, excluded/uncertain entries and the reasons for any recommendation. User-selected weighting and alternatives are valid when transparent. Save a report only in the requested scope and destination; no fixed deliverables folder or automatic next workflow.

## Outputs and records

Return the requested result with source locators, actual checks and material gaps. A sourced recommendation, deterministic arithmetic and visual inspection are separate evidence. Use the [completion contract](../../docs/completion-reporting.md). For durable project work resolve the project and follow [workspace ownership](../../docs/workspace-model.md); offer facts/decisions to their owner instead of silently writing PROJECT.md. One-off work remains standalone.

If consuming an existing epd-library.csv, apply `product_library.validate` with `kind: "epd"`
under the [EPD library owner](../../tools/workspace/epd-library-contract.md). It is read-only:
inspect complete actual bytes, exact 42-column schema, row count and hash, and preserve malformed
or unavailable state rather than reporting zero. Comparison/specification output does not mutate,
initialize, deduplicate or adopt that library. Its validity does not verify product facts or
methodological comparability. Requested saved outputs follow the public-output custody above.