Readability for Technical Documentation: Clarity First
Readability formulas measure sentence and word length, not precision. See two scored examples and a practical way to use scores on technical docs.
Technical writers are often told to hit a grade level. For documentation, that target can mislead. A formula can tell you a sentence is long. It cannot tell you whether the instruction is correct or complete.
Scores below come from this site's calculator, run on 9 October 2026. The sample text was written for this post.
What the formulas measure
Flesch published his Reading Ease formula in 1948. The Flesch-Kincaid Grade Level came from a 1975 US Navy study of training manuals. Both use the same two inputs: words per sentence and syllables per word.
Gunning Fog and SMOG count words of three or more syllables. Coleman-Liau and ARI count letters. None of them reads for meaning.
Example 1: removing the term does not help much
Configure the webhook endpoint to receive POST requests from the payment service.
Grade 8.8.
Set up a web address that the payment service can send messages to when something happens.
Grade 7.6.
The plain version is four words longer and about one grade lower. It also loses "webhook" and "POST," the words a developer would search for and need to type. For this reader, the first sentence is the clearer one.
Example 2: splitting the steps helps a lot
To rotate the signing key without interrupting service, first generate a replacement key in the console, then add it to the configuration file alongside the existing key, deploy the change to every instance, and finally remove the original key once all instances report the new version.
One sentence, 46 words. Grade 22.6.
You can rotate the signing key without downtime. First, generate a new key in the console. Add it to the configuration file next to the old key. Deploy the change to every instance. When all instances report the new version, remove the old key.
Five sentences, 44 words. Grade 4.7.
Every technical term survives: signing key, console, configuration file, instance. The gain came from giving each step its own sentence.
What to do instead of chasing a grade
- Keep exact terms. Use the names in your product and API. Use one name for one thing.
- Define a term once, where it first appears, and link to a glossary.
- One step per sentence. Use a numbered list for procedures.
- Put conditions first. "If the build fails, check the log" is easier than the reverse.
- Use headings and lists so readers can scan to the part they need.
- Do not add claims. A rewrite must not say more than the original did.
How to use a score
Use it as a flag, not a goal.
- Score the page in the readability checker.
- Look at the red sentences, which are over 25 words. Most of them hold several steps.
- Split them. Leave the technical terms alone.
- Ask someone to follow the page and complete the task. That test tells you more than any score.
If syllable counts look wrong for your product names, compare with a letter-based formula. Our post on Coleman-Liau explains how it works, and the formula guide compares all six.
How we checked
Both examples were scored on this site's calculator. The formula history comes from the 1948 and 1975 sources linked above. An earlier version of this post cited two studies we could not find. They have been removed.
Frequently asked questions
What readability score should technical documentation have?
There is no standard score for technical docs. Formulas measure sentence length and word length, and they cannot judge precision. Use the score to find long sentences, then check the result with real readers doing real tasks.
Should I replace technical terms to lower the grade?
Usually not. A developer expects the exact term and may search for it. Keep the term, define it once, and shorten the sentences around it.
Which formula is best for technical writing?
None is proven best. Coleman-Liau and ARI count letters, so they avoid syllable-counting errors on unusual terms. Whichever you pick, use the same one every time so your numbers compare.