ISO 24495-3 Technical Plain Language

ISO 24495-3:2026 - Plain Language (Science and Technical Communication)

Proxy status: These rules are this project's own proxies for the standard's principles, not its text. Following them is never a claim of ISO conformance.

Extends ISO 24495-1:2023 for software architecture, technical documentation, algorithm explanations, code reviews, and scientific analysis.

Scope & Execution Boundaries

1. Thinking Block Exemption:

   • Internal architectural analysis, code reasoning, and mental trace blocks (the thought and thinking tags) are 100% exempt from plain language constraints.
   • Reason freely within thinking blocks. Apply plain language rules strictly to final user-facing technical text.

2. Code & Data Preservation Immunity:

   • Code blocks, stack traces, abstract syntax tree (AST) dumps, terminal commands, and exact line quotes are completely immune to sentence length and simplification constraints. Never alter, abbreviate, or mangle working code or logs to fit text constraints.

3. Document Design Applies Here Too:

   • A technical document is a document, so iso-24495-5 loads alongside this skill. Part 5 governs headings, navigation, chunking, signalling, and readers who cannot see the page.
   • It loads for a document, not for every explanation. A code review comment and a chat answer are explanations, and the rules below still govern them.
   • Where the two appear to conflict, follow the resolution named in the rules below.

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Quantitative Rules & Hard Constraints (User-Facing Output)

1. Progressive Disclosure Ordering: Structure every technical explanation in these stages, in this order:

   1. System Purpose: High-level operational intent (1 sentence).
   2. Architecture & Data Flow: Diagram (Mermaid) or summary table. Rule 4 governs the diagram's text alternative, and Part 5 governs the table. Required where the explanation covers how more than one component relates to another. A single mechanism needs none, and neither does a sequence of steps that an ordered list already presents in order. A diagram nobody needs is the decoration Part 5 forbids.
   3. Implementation Detail: Concrete code snippet with exact file citations.

   These stages order an explanation, and Part 5's three levels order a document. They are different axes rather than two versions of one, so they do not map one to one. Where the explanation is a document:

   • The purpose sentence supplies the purpose line of Part 5's opening block, and opens its overview where Part 5 calls for one. The block's title, version and named reader are not its to supply, and Part 5 still requires them of the author. That overview also keeps the conclusion, the action required and any essential qualification, which one sentence does not.
   • Stages 2 and 3 sit in the main body, in that order.
   • Part 5's optional detail holds what a reader can skip and still act on. No stage covers it, so nothing is demoted there by default.

   A stage covers what the explanation contains. A runbook explains what to do and a decision record explains a choice, so neither needs stage 2's diagram of components nor stage 3's code. Omit a stage the explanation has no content for, and keep the order of those it has. They also do not exclude what a genre needs beside them: an incident report's timeline sits with the stages rather than inside one.

2. File & Code Citation Standard:

   • Quote exact file locations using markdown links with line numbers: [filename](file:///path/to/file#L10-L20).
   • Never describe code changes or logic without citing the exact file and line range. This governs an explanation of code. A guide describing what a user does needs no citation.

3. Terminology & Acronym Standardisation:

   • Define every acronym or domain-specific term upon first use in parentheses (e.g. "Abstract Syntax Tree (AST)").
   • Use consistent symbol names across text, code snippets, and diagrams.

4. Diagrams and Their Alternatives:

   • Give every diagram a text alternative saying what it shows, not what it is. Part 5 requires that of any image carrying meaning. Stage 2 above offers a diagram as one way to meet it, so this rule says where the alternative goes. A summary table is the other way, and Part 5 already governs it.
   • A Mermaid diagram reaches a listener as its source text, which is not an explanation. So the alternative is prose beside the diagram, never the diagram's own labels.