Simplified Technical English (ASD-STE100)

ASD-STE100 is a controlled-language standard built by the aerospace and defense industry (ASD, the AeroSpace and Defense Industries Association of Europe) to stop maintenance technicians from misreading English instructions. The standard removes the two biggest sources of misreading: words with more than one meaning, and sentences with more than one possible structure.

This skill borrows that same discipline for a different reader: an AI agent or a downstream system that has to parse an English string — an error message, a tool description, an inter-agent instruction, a status report — without a human in the loop to resolve ambiguity. If a maintenance technician can misread "close the valve" as an adjective ("the valve that is near") instead of a command, so can a language model.

When to Use This Skill

• An agent's output (explanation, instruction, log message, tool description) reads as dense, jargon-heavy, or ambiguous.
• Text will be consumed by another agent, a translation pipeline, or a non-native English reader, and misparsing has a real cost.
• You are writing a prompt, system message, or tool description and want to remove ambiguity before a model ever sees it.
• You want a before/after comparison showing exactly which rule was violated and how the rewrite fixes it. Ask for it — the default output is the rewritten text alone (see Output Format).

This skill is not for creative or marketing copy — STE is deliberately flat and literal. Do not apply it to text where voice, nuance, or persuasion is the point.

Two Modes

Pick a mode before rewriting. If the user does not say which, infer it from the text type. Keep the choice internal unless the user asks for the rule table (see Output Format).

Strict — procedures, error messages, tool and function descriptions, inter-agent instructions, safety text. Anywhere a wrong reading has a cost. Apply every rule below, including the hard length caps and one-word-one-meaning discipline.

STE-flavored — READMEs, PR descriptions, changelogs, explanatory prose. Apply the structural rules in full and treat the lexical rules as advisory (see Core Rewrite Rules for that split). In practice that means keeping the sentence length caps, active voice, simple tenses, no phrasal verbs, no semicolons, no nominalization and no marketing adjectives, while dropping the one-word-one-meaning lockdown: prose needs some range, and a strict rewrite of prose reads as a personality transplant rather than a clarification.

The two modes and the structural/lexical split are the same distinction seen from two directions. The split says which rules this skill can verify without ASD's dictionary. The modes say which of them to enforce for a given kind of text.

Source and Scope

This skill encodes the rule categories of ASD-STE100 Issue 9 (Jan 2025): 53 writing rules across 9 sections covering word choice, grammar, sentence structure, and style, backed by a dictionary of ~900 approved words (one meaning, one part of speech each) and ~1,200 words to avoid with suggested replacements. See references/writing-rules.md for the full rule summary and citations.

It does not reproduce ASD's ~900-word approved dictionary verbatim. ASD-STE100 is free to obtain, but it is not free to redistribute: Issue 9, page 2 states that "no reproduction or publication of it, in whole or in part, shall be made without the written authority of an officer of ASD," and grants free reproduction rights only to eight listed categories (ASD/AIA/AIAC member associations and their member companies and customers, member-state defence ministries, A4A, airworthiness authorities, and universities and research institutes for educational purposes). This project is in none of them, so the dictionary stays out of this repo.

Instead, this skill applies the underlying principle (pick the plainest, most common word available and use it the same way every time) rather than checking against a fixed word list. When exact ASD-approved wording matters (e.g. actual aircraft maintenance documentation), get the standard and check word-by-word against the real dictionary. Request it from the official downloads page — note that this is a request form that emails you a link, not a direct download.

Core Rewrite Rules

STE's rules divide into two kinds, and this skill can only fully deliver one of them. Structural rules are self-contained: they describe sentence shape, and you can apply them from the description alone. Lexical rules are defined entirely by the official ~900-word dictionary, which this skill deliberately does not reproduce (see Source and Scope). Without that dictionary, the lexical rules degrade from a checkable standard into a preference for plain words.

Apply the structural rules with confidence. Apply the lexical rules as a direction of travel, and say so in your output rather than implying dictionary compliance you cannot verify.

Structural rules — apply these

Lexical rules — direction of travel only

Simple tenses — apply with one exception

STE permits infinitive, imperative, simple present, simple past, simple future, and past participle as adjective. It excludes present perfect and other compound forms: "we received the report", not "we have received the report".

Aircraft manuals never need present perfect, so the exclusion costs the standard nothing. Other text is not always so lucky. "The job has completed" (and its output is available now) and "the job completed" (at some past point) are different statements, and status text frequently needs the first. Where the compound form carries information the simple form cannot — current relevance, or a hedge as in "may have failed" — keep it and flag the departure. Elsewhere, follow the rule.

Scan Checklist

These six habits cover most of what makes machine-written English hard to parse. Each one is mechanical: you can point at the exact word or punctuation mark that breaks the rule, with no judgment call. Scan for all six before you rewrite anything.

1. Synonym rotation — the same thing gets several names in one document ("the user", "the customer", "the client"). The reader cannot tell whether they are one thing or three. Fix: pick one name, use it every time.
2. Hedge stacking — helper verbs and qualifiers pile up until the sentence asserts nothing ("it is important to note that this may potentially help to improve"). Fix: state the claim, or delete it.
3. Nominalization — an action frozen into a noun ("perform an analysis of", "provides assistance to"). Fix: use the verb ("analyze", "helps").
4. Marketing adjectives — words that claim quality instead of showing it: seamless, robust, powerful, cutting-edge, effortless, blazing-fast. Fix: delete, or replace with the measurement that earns the claim.
5. Run-on sentences — several ideas joined by semicolons or em dashes. Fix: one idea per sentence.
6. Soft phrasal verbs — spin up, reach out, dive into, kick off. Fix: use the single plain verb (start, contact, read, begin).

Process

1. Pick the mode (Strict or STE-flavored). Say which only when the user asked for the rule table — see Output Format.
2. Read the input text once for meaning — do not start rewriting before you understand what it must still say afterward.
3. Walk it sentence by sentence. Flag every rule violation from the Core Rewrite Rules tables and every habit from the Scan Checklist. In STE-flavored mode, flag the lexical rules but do not enforce them. For a mechanical first pass over the structural rules, run scripts/ste-lint.py (stdin or file args, --json for structured output); it checks semicolons, sentence length, phrasal verbs, nominalization, marketing adjectives, synonym rotation, dangling-conjunction in supported list items, passive voice, and compound tenses, and by design never flags hedges or modality. --baseline N tolerates N hard violations (for adopting on existing docs); --disable rule1,rule2 silences named rules.
4. Rewrite each flagged sentence to fix the violation while preserving the original meaning exactly. If a rewrite would drop necessary precision (a safety condition, a scope qualifier, a number), keep the longer phrasing and flag it instead of silently simplifying.
   • Check modality before you commit to a rewrite. Hedges ("may", "could", "sometimes", "is likely to") carry the author's confidence, and confidence is content. A shorter sentence that upgrades a hedge to a fact is not a simplification — it is a different claim. This is the most common way a well-intentioned STE rewrite goes wrong, because hedges are exactly what a length cap tempts you to cut.
   • Never add a fact the source did not state. A rewrite that reads better because it supplies a cause, a frequency, or a mechanism has stopped being a rewrite.
5. Output the rewritten text (see Output Format). Keep the mode choice and the rule analysis internal unless the user asked to see them.
6. If the input already complies, say so — do not force changes onto compliant text.

Output Format

Default: the rewritten text, and nothing else. Most callers want a result they can paste straight into a tool description, an error string, or a prompt. Print the simplified text on its own. Do not add a preamble about this skill, a mode announcement, a violation count, a summary of what changed, a rule table, or a closing offer to explain further.

The one permitted addition: if step 4 kept a longer phrasing on purpose, add a single line after the text, prefixed Kept as-is:, naming the phrase and the precision that would have been lost. Omit the line when there is nothing to report.

On request: the rule table. When the user asks to see the reasoning — "show the diff", "which rules did it break", "explain the changes", "before/after" — output this table instead:

| Rule violated | Original | Simplified |
|---|---|---|
| Present perfect tense | "We have received your request." | "We received your request." |
| Noun cluster (4+ words) | "the agent task queue priority handler" | "the handler that sets task-queue priority" |

Mode: Strict. 7 violations found.

Follow the table with a one-line note on anything you deliberately did not simplify, and why (usually: simplifying would lose required precision).

Boundaries

Will:

• Rewrite ambiguous or dense English into short, single-meaning, active-voice sentences.
• Return the rewritten text alone by default, and name the rules it applied when the user asks.
• Preserve every fact, condition, and scope qualifier in the original.
• Preserve the strength of every hedge, and add no claim the source did not make.
• Suggest a one-line glossary entry for domain terms that must stay.

Will not:

• Reproduce ASD's official ~900-word dictionary as if it were memorized verbatim — always treat the official download as the source of truth for exact approved wording.
• Simplify creative, marketing, or persuasive copy where voice and nuance are the point.
• Silently drop a safety condition, exception, or scope qualifier to shorten a sentence — it will flag the trade-off instead.
• Convert "may have failed" into "failed", or "could be caused by X" into "X is the cause" — losing a hedge changes the claim.
• Guarantee an aerospace/defense-grade STE-compliant document. This is a general-purpose clarity tool inspired by STE, not a certified STE authoring tool.
• Make weak content true or useful. STE fixes the form of a text, not its substance. A hollow paragraph rewritten under these rules becomes a clean, short, well-punctuated hollow paragraph. If the text has nothing to say, no rewrite fixes that — say so instead of polishing it.
• Shorten past the point of clarity. Cutting words is not the goal. Removing ambiguity is the goal. Past a certain point compression starts costing the reader time rather than saving it, so stop when the sentence is unambiguous, not when it is shortest.

Additional Resources

• references/writing-rules.md — fuller summary of the 9 rule sections and dictionary structure, with citations to the official standard and secondary sources.
• examples/before-after.md — worked examples, including official STE examples and agent-output examples built for this skill.
• scripts/ste-lint.py — deterministic, stdlib-only linter for the structural rules, including dangling-conjunction in supported list items, plus a synonym-rotation check (one word, one meaning) scoped per file. Exit 1 when hard violations exceed --baseline (default 0); advisory findings (passive voice, compound tenses) never fail the run; --disable silences named rules. It never flags hedges or modality: those are content, not style, and --selftest asserts that "may have failed" passes clean.