In one paragraph
Simplified Technical English exists because a maintenance instruction written in one country is read by a technician in another, often in a second or third language, sometimes under time pressure and occasionally in conditions where misreading it is dangerous. ASD-STE100 is the standard that addresses that, and it has two parts that only work together. Part 1 is 53 writing rules across nine sections, covering words, verbs, sentences, procedures, descriptive text, safety instructions and punctuation. Part 2 is a controlled dictionary of roughly 2,000 entries, each approved word carrying the part of speech and the specific meaning it is approved for, and each non-approved word carrying the alternative to use instead. People arriving at the standard tend to read the rules and skim the dictionary. The dictionary is the part that changes how you write.
If you already know why this matters and want to get an AI system to actually produce compliant text, how to make an LLM write in Simplified Technical English is the more direct guide.
The two parts
The rules are organised into nine sections. Section 1 covers word choice and technical nouns. Section 2 covers multi-word nouns. Section 3 covers verbs, which is where the standard is at its most restrictive. Section 4 covers sentence construction, section 5 procedural writing, section 6 descriptive writing, section 7 safety instructions. Section 8 covers punctuation and the rules for counting words, and section 9 covers writing practices that apply throughout.
The dictionary lists approved words with their approved part of speech and meaning, and non-approved words with their approved alternatives. An approved word is not approved generally. It is approved as a specific part of speech, carrying a specific meaning. "Follow" is approved, meaning to come after or go after. Using it to mean comply with an instruction is a deviation, and the approved word for that is "obey".
Approved meanings and spelling are based on American English.
What surprises people
The vocabulary is smaller than expected, and narrower. Ordinary, unremarkable words are frequently not approved, and the ones that are often carry a single permitted sense.
Verbs lose most of their tenses. Six verb forms are permitted. Present perfect, past perfect and both progressive forms are out, which removes a great deal of how technical writing is habitually constructed. "The panel has been removed" and "the system is checking the input" are both deviations.
The passive voice is nearly gone. Procedures are always active or imperative. Descriptive text permits the passive only where the agent is genuinely unknown, which is a narrower exception than it first appears.
There is a hard word limit. Twenty words for a procedural sentence, warning or caution. Twenty-five for descriptive text and for notes. Six sentences maximum in a paragraph.
The semicolon is prohibited outright. Every other standard punctuation mark is permitted. The semicolon is not, whatever the relationship between the clauses.
Counting words is itself specified. A number with its unit counts as one word. An abbreviation counts as one. A hyphenated group counts as one. A parenthetical remark counts as one word of its sentence, and separately as its own sentence for its internal count. Those rules exist because without them the length limits would be arguable.
What it is not
It is not a style guide. It is a specification, and its rules are testable.
It is not a complete grammar reference and cannot be used alone. It is meant to sit alongside the technical publication specifications and directives that already apply to your documentation.
It does not cover everything. Abbreviations, text formatting, numbering, and units of measurement are outside its scope, and are left to whatever other specifications apply.
It is not automatically satisfied by writing simply. Plain English and STE overlap and are not the same thing. Text can be clear, short and entirely non-compliant.
Who uses it
It originated in aerospace and defence technical documentation, which is still where it is most often contractually required. The discipline travels further than that, and organisations outside those sectors adopt it wherever documentation is read by non-native English speakers or where ambiguity carries a real cost.
It is also becoming interesting for a reason it was not designed for. A controlled language standard is a specification a machine can be held to, which makes it one of the few concrete answers to the problem of verifying that generated text conforms to anything. That is the subject of deterministic work belongs either side of the model call.
ASD has taken a position on that use. Its Maintenance Group's June 2026 white paper accepts AI as a support for STE writing and translation, on the conditions that the standard takes priority, a person stays responsible for the text, and AI-assisted content is declared as such with its limits stated.
Where to start
Read the 53 rules with their worked examples, which is a shorter exercise than it sounds. Then take one of the published prompts and run a page of your own documentation through it, because the abstract rules become concrete the moment they are applied to writing you recognise. For the mechanics of getting an LLM to actually produce compliant output, see how to make an LLM write in Simplified Technical English.
If you need the standard itself, obtain it directly from ASD(opens in a new tab); it is free to request. ASD's June 2026 white paper on STE and AI(opens in a new tab) states the Maintenance Group's position on the use of AI with the standard; this guide is consistent with it. This site publishes commentary on the rules and does not reproduce the standard.