Anthropic¶
What the anthropic/default files change, laid over the default rules for every anthropic: model. Every rule not listed here reads as it does by default. These models also have files of their own: anthropic/claude-fable-5-1, anthropic/claude-opus-5, anthropic/claude-opus-5-5, anthropic/claude-sonnet-5-5. Any other anthropic: model reads the default rules and this page's changes.
wording¶
Released 2026-10-07; a pin reads it as wording = "1.0.0" under [lint.rules].
Writing for anthropic/default
Current Claude models overtrigger on loud emphasis.
- Drop capitals and exclamation marks: Opus 4.5 to 5.5 and Sonnet 4.6 overtrigger on them.
Sources: Anthropic, Prompting best practices; Anthropic, Prompting Claude Fable 5, Sonnet 5, Opus 4.8 and Opus 5; Anthropic skills repository, prompt-audit guide.
From anthropic/default, 1.0.0.
| Rule | Finds | Default | On anthropic: models |
|---|---|---|---|
wording/capitals |
Emphasis in capitals | info | warn on claude-opus-4-5, claude-opus-4-6, claude-sonnet-4-6, claude-opus-5, claude-opus-5-5; info on the rest |
wording/exclamation-marks |
Repeated exclamation marks | info | warn on claude-opus-4-5, claude-opus-4-6, claude-sonnet-4-6, claude-opus-5, claude-opus-5-5; info on the rest |
instructions¶
Released 2026-10-07; a pin reads it as instructions = "1.0.0" under [lint.rules].
Writing for anthropic/default
Current Claude models follow a plain instruction with its reason better than a bare one.
- Say what to do instead of what not to do; keep a prohibition for a real business rule, with its reason.
- Give the reason with the rule: Claude generalises from the reason to cases the rule never names.
Sources: Anthropic, Prompting best practices; Anthropic, Prompting Claude Fable 5, Sonnet 5, Opus 4.8 and Opus 5; Anthropic skills repository, prompt-audit guide.
From anthropic/default, 1.0.0.
| Rule | Finds | Default | On anthropic: models |
|---|---|---|---|
instructions/default-when-unsure |
Makes a tool the default when in doubt | info | warn on claude-opus-4-5, claude-opus-4-6, claude-sonnet-4-6, claude-opus-5, claude-opus-5-5; info on the rest |
reasoning¶
Released 2026-10-07; a pin reads it as reasoning = "1.0.0" under [lint.rules].
Writing for anthropic/default
Thinking is a setting on current Claude models: effort and the thinking mode, not prose.
- Set effort in the request instead of writing 'think step by step' or 'don't overthink'.
- Do not ask Fable 5 or 5.1, Opus 5 or 5.5, or Sonnet 5.5 to show their reasoning: their safeguards refuse it. Ask for a short justification after the answer instead.
Sources: Claude API docs: Extended thinking, Effort, Refusals; Anthropic, Prompting best practices; Anthropic skills repository, prompt-audit guide.
From anthropic/default, 1.0.0.
| Rule | Finds | Default | On anthropic: models |
|---|---|---|---|
reasoning/show-reasoning |
Asks to see the model's reasoning | warn | error on claude-fable-5, claude-fable-5-1, claude-opus-5, claude-opus-5-5, claude-sonnet-5-5; warn on the rest |
output¶
Released 2026-10-07; a pin reads it as output = "1.0.0" under [lint.rules].
Writing for anthropic/default
Fable 5.1 and Sonnet 5.5 narrate progress between tool calls; the request settings decide where updates go.
- Ask for progress updates in the request (display 'updates') rather than writing 'hold all findings' or 'don't narrate'.
- Ask for JSON with structured outputs or a strict tool, not with 'output ONLY valid JSON'.
Sources: Claude API docs: Structured outputs, Errors, thinking display; Anthropic, Prompting Claude Sonnet 5.5; Anthropic skills repository, prompt-audit guide.
From anthropic/default, 1.0.0.
| Rule | Finds | Default | On anthropic: models |
|---|---|---|---|
output/hold-progress |
Holds back progress updates | info | warn on claude-fable-5-1, claude-sonnet-5-5; info on the rest |