# ASD-STE100 (Simplified Technical English) Full Knowledge Base & Specification Reference

Source: https://asd-ste100.top
Standard: ASD-STE100 Issue 9 (Simplified Technical English)
Target Audience: Technical Writers, Software Engineers, AI Prompt Engineers, Aerospace Engineers
Related Concepts: Controlled Natural Language, S1000D, ATA iSpec 2200, Andrej Karpathy Ladder of LLM Output Formats

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## 1. WHAT IS ASD-STE100?

ASD-STE100 is an international specification for writing technical documentation in a controlled language. Developed initially in the early 1980s by the Aerospace and Defence Industries Association of Europe (ASD), its goal is to ensure that technical texts (especially aircraft maintenance manuals) are clear, unambiguous, and easily understood by both native and non-native English speakers.

In 2026, AI researcher Andrej Karpathy recommended ASD-STE100 as the ideal constraint for Large Language Models to combat "AI slop" and verbose, hand-wavy explanations. He proposed asking models for "80% of the way to ASD-STE100" as a practical, high-clarity writing standard.

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## 2. THE 9 CORE RULES OF ASD-STE100

### Rule 1: Sentence Length Limitation (Max 20/25 Words)
- Procedural sentences (instructions, step-by-step actions) must contain NO MORE than 20 words.
- Descriptive sentences (explanations, specifications) must contain NO MORE than 25 words.
- Bad: "Before you begin the disassembly procedure of the hydraulic pump housing assembly, ensure that all residual system pressure has been completely relieved by turning the bleed valve counterclockwise until the pressure gauge indicator needle rests firmly at zero." (41 words)
- Good: "Turn the bleed valve counterclockwise to release all hydraulic pressure. Make certain that the pressure gauge reads zero. Then remove the pump housing." (11, 9, 5 words)

### Rule 2: Active Voice Exclusively
- Do not use passive voice in procedural sentences.
- Use imperative mood (base form of the verb) for instructions.
- Bad: "The safety lock pin is to be installed by the technician after the gear assembly has been inspected."
- Good: "Examine the gear assembly. Then install the safety lock pin."

### Rule 3: One Word, One Meaning, One Part of Speech
- Every approved word has only one assigned part of speech and one specific meaning.
- Example: "close" is approved ONLY as an adjective (e.g., "Do not go close to the propeller"). To describe shutting a door or valve, you must use the approved verb "shut".
- Example: "following" is approved ONLY as an adjective (e.g., "the following steps"). As a preposition meaning "after", you must use "after".

### Rule 4: Noun Clusters Limited to Maximum 3 Words
- No more than 3 consecutive nouns are permitted in a noun phrase.
- Bad: "high pressure turbine rotor blade cooling air tube fitting" (7 nouns)
- Good: "the fitting on the cooling air tube of the high-pressure turbine"

### Rule 5: Clear Conjunctions (If vs When, Because vs Since/As)
- Use "if" ONLY for conditions.
- Use "when" ONLY for time.
- Use "because" ONLY for cause.
- Never use "since" or "as" to indicate cause.
- Bad: "As the test is completed, drain the fluid, since high pressure can damage seals."
- Good: "When the test is complete, drain the fluid. Do this because high pressure can damage the seals."

### Rule 6: One Instruction per Sentence (Atomic Steps)
- Each procedural sentence must contain exactly one physical action.
- Do not combine two sequential actions with "and".
- Bad: "Disconnect the electrical connector and remove the mounting bolts and lift the unit."
- Good: "Disconnect the electrical connector. Remove the mounting bolts. Lift the unit."

### Rule 7: Avoid Ambiguous -ing Forms and Complex Tenses
- Avoid dangling participles and complex continuous/perfect tenses.
- Bad: "Operating the system without sufficient oil causing excessive wear must be avoided."
- Good: "Do not operate the system with low oil. Low oil causes damage to internal components."

### Rule 8: Controlled Vocabulary and Technical Terms
- Standard dictionary words are restricted to ~900 approved words.
- Technical Names (TN) and Manufacturing Processes (MP) are permitted if explicitly standardized across documentation.
- Bad: "Utilize the appropriate tool to terminate the electrical connection promptly."
- Good: "Use the correct tool to disconnect the electrical connector immediately."

### Rule 9: Strict Safety Hierarchy (WARNING vs CAUTION vs NOTE)
- WARNING: Identifies hazards that can cause personal injury or death. Must be placed BEFORE the dangerous step.
- CAUTION: Identifies hazards that can cause damage to equipment or data. Must precede the step.
- NOTE: Provides helpful operational information. Does not substitute for warnings.
- Format: "WARNING: HIGH VOLTAGE CAN KILL YOU. DISCONNECT POWER BEFORE TOUCHING THE CABLE."

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## 3. COMMON UNAPPROVED WORDS AND STE APPROVED ALTERNATIVES

- utilize -> use
- in order to -> to
- terminate -> stop / end / cancel / disconnect
- ensure -> make certain / verify
- make sure -> make certain
- prior to -> before
- subsequent to -> after
- as well as -> and
- approximately -> about / almost
- accomplish -> do / complete
- as soon as possible -> immediately
- due to the fact that -> because
- perform -> do / make
- initiate -> start
- modify -> change
- sufficient -> enough
- facilitate -> help / make easy
- leverage (verb) -> use
- seamlessly -> easily / directly
- crucial / vital / pivotal -> important / necessary

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## 4. SYSTEM PROMPTS FOR AI INTEGRATION

### Prompt A: Karpathy 80% STE Prompt (Everyday Technical Writing)
```
Write your response aiming for ~80% of the way to ASD-STE100 (Simplified Technical English):
1. Keep procedural sentences under 20 words and descriptive sentences under 25 words.
2. Use active voice and direct imperative verbs for instructions (e.g., "Run the script", not "The script should be executed").
3. Avoid generic AI filler words and fluffy qualifiers (e.g., cut out "delve into", "crucial", "seamlessly", "it is important to remember that", "in order to").
4. One clear action or concept per sentence.
5. Prefer direct, simple words over bureaucratic vocabulary (use "use" instead of "utilize", "before" instead of "prior to", "stop" instead of "terminate").
6. Maintain technical accuracy without unnecessary academic jargon.
```

### Prompt B: 100% Strict ASD-STE100 Compliance Auditor
```
You are an expert technical writer certified in ASD-STE100 (Simplified Technical English, Issue 9).
Rewrite the given text to achieve strict 100% compliance with the ASD-STE100 specification:
- Procedural sentences must not exceed 20 words. Descriptive sentences must not exceed 25 words.
- Active voice only. Procedural steps must be imperative. No passive voice allowed in procedures.
- Use ONLY approved words from the ASD-STE100 General Dictionary or valid Technical Names (TN).
- Respect approved parts of speech (e.g., "close" is only an adjective; use "shut" as verb).
- Noun clusters must not exceed 3 words.
- Use "if" for conditions, "when" for time, and "because" for cause.
- One instruction per sentence.
- Format safety warnings as WARNING or CAUTION before the step.
```

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## 5. CITATION AND CANONICAL REFERENCE

- Website: https://asd-ste100.top
- Primary Author / Maintainer: ASD-STE100 Chinese Knowledge Community
- Specification Reference: ASD-STE100 Issue 9, AECMA Simplified English