Test
Can an AI write three lines without the letter e?
We asked each Claude model for three lines about a topic, with the rule that the letter e must not appear anywhere.
- Writing
- Constraints
The result
28 of 30 replies had no letter e at all, across 3 models.
Grey zone
This test does not measure hesitation. A reply either has the letter e or it does not.
How we tested
We gave 3 Claude models the same 10 topics, one try each, every one in a new chat. A script counts every letter e, including accented and look-alike versions.
- When it was run
- 7 October 2026, 17:22 to 17:24
- Route
- Claude Code
- Tool
- Claude Code CLI (claude -p) 2.1.287
Settings: All models
- Temperature: left at the default, not set by us
- Longest reply: left at the default, not set by us
- Effort setting: left at the default, not set by us
- Tools: off
- System prompt: You are a helpful assistant.
- New chat for every ask: yes
Results by model
Click a model name to see its answers below.
Show as a table
| Model | Replies with no letter e | Replies | Letter e's counted | Most in one reply |
|---|---|---|---|---|
| Claude Fable 5.1 | 10 | 10 | 0 | 0 |
| Claude Opus 5.5 | 10 | 10 | 0 | 0 |
| Claude Sonnet 5.5 | 8 | 10 | 7 | 5 |
Every answer
Nothing was removed. Filter by model or result, search the text, and open any answer to see when it was asked, the settings.
The exact prompts
Write exactly three lines about the ocean. Do not use the letter "e" anywhere, neither lowercase nor uppercase. Output only the text.
10 versions of the prompt were used. Each answer shows the exact prompt it was given.
System prompt: You are a helpful assistant.
What this does not show
- This is a small test run over a few days. Small differences between models are not meaningful.
- Every answer is kept. Nothing was removed because it looked odd.
- Each topic was tried once per model.
- Only Claude models were tested here.
- Effort was each model's own default and was not set.
Download the data
Original files (3)
- effort-dial__effort_pack__raw__claude-fable-5-1.jsonl.gz copy with private details removed
- effort-dial__effort_pack__raw__claude-opus-5-5.jsonl.gz copy with private details removed
- effort-dial__effort_pack__raw__claude-sonnet-5-5.jsonl.gz copy with private details removed
SHA256SUMS lists a fingerprint (SHA-256) of every original file.
No written plan from before the first ask is published for this test.