SillyTavern Free API Setup in 2026 (and the "Bad Request" Fix)

By Updated 1 min read

Quick answer

In SillyTavern open API Connections, choose Chat Completion with the Custom (OpenAI-compatible) source, enter https://api.freetheai.org/v1 as the endpoint, your FreeTheAI key, and a model like fta/zai/glm-5.3, then set Prompt Post-Processing to Semi-strict.

Key takeaways

  • Use the base URL ending in /v1; SillyTavern adds /chat/completions itself.
  • Semi-strict Prompt Post-Processing fixes most "Bad Request" errors.
  • Save the setup as a Connection Profile to switch models in one click.

The settings

SillyTavern settings for FreeTheAI
FieldValue
APIChat Completion
Chat Completion SourceCustom (OpenAI-compatible)
Custom Endpoint (Base URL)https://api.freetheai.org/v1
Custom API KeyYour full ftai_... key
Model IDfta/zai/glm-5.3
Prompt Post-ProcessingSemi-strict (alternating roles)

Step by step

  1. Click the plug icon in the top bar to open API Connections.
  2. Set API to Chat Completion and Chat Completion Source to Custom (OpenAI-compatible).
  3. Paste the base URL into Custom Endpoint. Do not add /chat/completions; SillyTavern does that.
  4. Paste your key into Custom API Key, type or pick a model ID, and press Connect.
  5. Set Prompt Post-Processing to Semi-strict.
  6. Do today's check-in and start chatting.

Fixing "API returned an error: Bad Request"

With Prompt Post-Processing set to None, SillyTavern can send a chat that has only the system prompt and the character's greeting, with no message from you. Some models refuse that and answer "Bad Request". Setting Prompt Post-Processing to Semi-strict makes sure every request carries a message from you, and the error goes away.

Other common problems

  • No models appear after connecting: type the model ID by hand, and check that you did today's check-in.
  • Replies cut off: raise Max Response Length in the sampler panel.
  • Unauthorized: paste the full 53-character key; the short prefix in your key list does not work.

Frequently asked questions

What base URL does SillyTavern need?

https://api.freetheai.org/v1. SillyTavern appends /chat/completions itself.

How do I fix "Bad Request" in SillyTavern?

Set Prompt Post-Processing to Semi-strict in API Connections, then try again.

Which model should I use in SillyTavern?

fta/zai/glm-5.3 is the best default. See our comparison of the best free roleplay models for alternatives.

About the author

founded FreeTheAI and builds and runs its API. He answers the support tickets these posts come from.

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