Response length

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Set up the Response Length evaluator

1

Open Evaluate from your prompt

Open the prompt you want to test and click Evaluate in the prompt header.

2

Select the evaluator

Add the Response Length evaluator from the evaluator menu.

3

Configure the threshold

Give the evaluator a name, link a dataset, and set the length threshold.Choose from the following threshold operators:

Operator	Behavior
less than	Responses must be shorter than your limit. Use this to enforce brevity.
greater than	Responses must be longer than your minimum. Use this to ensure sufficient detail.
equal to	Responses must match an exact length requirement.

4

Select the unit of measure

Choose how length is measured.

Unit	Description
Tokens	Exact token count as returned by the LLM provider. Most accurate for cost and context limit management.
Words	Number of words (sequences of characters separated by whitespace). Easier to reason about for content length.
Characters	Total character count. Best for strict UI or display constraints.

5

Run the evaluation

Click Evaluate to execute the evaluation and see the results.

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When to use

• UI constraints — Ensure responses fit within character limits for display components (chat bubbles, cards, notifications).
• Content consistency — Enforce a consistent level of detail across all responses.
• Brevity enforcement — Prevent the model from generating overly verbose outputs.
• Minimum detail requirements — Ensure responses contain enough information to be useful.
• Token budget management — Work alongside the Cost evaluator to keep token usage in check.

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Next steps