# ReAct prompting

**Source:** https://promtable.com/glossary/react-prompting

> ReAct interleaves reasoning steps with tool actions, letting a model think, act, observe, and repeat until it answers.

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ReAct interleaves reasoning steps with tool actions, letting a model think, act, observe, and repeat until it answers.

ReAct ("Reason + Act") is a prompting pattern where the model alternates between writing a reasoning step ("Thought"), taking an action against a tool ("Action", e.g. a search or calculator call), and reading the result ("Observation"), looping until it has enough to answer. Unlike pure chain-of-thought, which reasons without external grounding, ReAct lets the model fetch facts mid-reasoning — reducing hallucination and enabling multi-step tasks like research, browsing, and database lookups. It is the backbone of most tool-using agents. Reliability comes from a clear action schema, a hard step cap, and an observation format the model can parse.

## When to use

- Agents that must call tools (search, code, APIs) to answer.
- Multi-step tasks where facts must be fetched, not recalled.
- Reducing hallucination by grounding each step in real observations.

## When not to use

- Closed-book questions the model can answer directly — the action loop is overhead.
- Latency-critical paths; each Thought-Action-Observation cycle is a round trip.

## Example

```
Input: Q: Who won the 2022 final and what was the score? Thought: I should search. Action: search[...] Observation: ...
Output: After one search-observe loop the model answers with the grounded result instead of guessing.
```

## Common mistakes

- No step cap — the loop runs away on hard or ambiguous queries.
- Free-text actions the runtime can't parse; define a strict action schema.
- Using ReAct when chain-of-thought (no tools) already suffices.

## Related terms

- [tree-of-thought](https://promtable.com/glossary/tree-of-thought)
- [chain-of-thought](https://promtable.com/glossary/chain-of-thought)
- [few-shot-prompting](https://promtable.com/glossary/few-shot-prompting)
- [prompt-engineering](https://promtable.com/glossary/prompt-engineering)

## Sources

- [ReAct (Yao et al., 2022)](https://arxiv.org/abs/2210.03629)

*Last updated: 2026-06-02*
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Original page: https://promtable.com/glossary/react-prompting
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