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llm-echo 0.5

Blog · Watch/Read · (gathered 2026-10-21)

  • Simon Willison released llm-echo 0.5, a debug plugin for his llm tool, which provides a mock “echo model” that simply repeats back prompts instead of engaging a real LLM.
  • The core functionality of llm-echo is to act as a placeholder LLM for testing purposes, outputting the input prompt and simulated metadata.
  • Version 0.5 introduces an enhancement to its simulated token usage counts, now accurately accounting for tool calls, system prompts, and reasoning tokens.
  • This plugin is practical for developers to test and debug LLM applications locally, avoiding the costs and latency of actual LLM API calls during the development phase.