# Tool Result

> The data returned to a model after an external tool call completes.

- Category: Tools & Protocols
- Stage: Established
- Also called: Observation, Tool output
- Canonical: https://www.joelcsaji.com/ai-dictionary/tool-result

## Plain English

It is what the agent sees after it acts.

## Example

A shell tool returns a failing TypeScript error, and the agent decides what to fix next.

## Why it matters

Tool results are the ground truth that keeps agents anchored to reality.

## Related

- [Agent Loop](https://www.joelcsaji.com/ai-dictionary/agent-loop)
- [Trace](https://www.joelcsaji.com/ai-dictionary/trace)
- [Grounding](https://www.joelcsaji.com/ai-dictionary/grounding)

## Sources

- [OpenAI: Function Calling](https://developers.openai.com/api/docs/guides/function-calling)
- [Anthropic: Building Effective Agents](https://www.anthropic.com/engineering/building-effective-agents)