Request Block

Mutating logic for inflight headers and JSON bodies.

The request block enables you to perform lightweight transformations on the payload before it gets sent to the upstream provider.

Header Operations

You can arbitrarily set, delete, or filter HTTP headers going to the upstream server.

request {
  set_header "x-trace-id" "trace-123";
  set_header "x-foo" concat("a-", $request.model_mapped);
  
  del_header "x-remove-me";

  # Remove specific values from a header (denylist)
  filter_header_values "anthropic-beta" "context-1m-*";

  # Keep only specific values in a header (allowlist)
  keep_header_values "anthropic-beta" "computer-use-*" "context-management-*";
}

Note: If the same header is set multiple times, the last one wins. Deletions and filter/keep operations apply in order.

filter_header_values

Removes header value items that match any of the given patterns (denylist). Non-matching items are kept.

request {
  filter_header_values "anthropic-beta" "context-1m-*" "fast-mode-*";
  filter_header_values "x-feature-flags" "exp-*" "debug" separator=";";
}

• Syntax: filter_header_values <header> <pattern>... [separator="<sep>"];
• Default separator is ,. Output is normalized (", " for comma, "<sep> " for others).
• Pattern matching supports * wildcards; case-insensitive is not applied (patterns must match the exact case used by the client).
• If all values are removed, the header is deleted.

keep_header_values

Keeps only header value items that match any of the given patterns (allowlist). Non-matching items are removed.

request {
  keep_header_values "anthropic-beta" "computer-use-*" "context-management-*";
  keep_header_values "x-feature-flags" "stable-*" separator=";";
}

• Syntax: keep_header_values <header> <pattern>... [separator="<sep>"];
• Mirror of filter_header_values with inverted logic: patterns select what to keep.
• Same separator and output formatting rules as filter_header_values.
• If no values match, the header is deleted.

Model Mapping

Use model_map to alias or hardcode model names conditionally.

request {
  model_map "gpt-4o-mini" "gpt4o-mini-prod";
  model_map "gpt-4o-mini" $request.model;
  
  model_map_default $request.model;
}

• Maps $request.model to $request.model_mapped.
• Exact match on the from string.
• If no matches occur, model_map_default dictates what $request.model_mapped becomes.

JSON Mutations

Apply lightweight mutations directly to the upstream JSON body.

request {
  json_set "$.stream" true;
  json_set_if_absent "$.instructions" "";
  
  json_rename "$.max_tokens" "$.max_completion_tokens";
  json_wrap_input_text "$.input";
  json_del "$.tools";

  # Populate a JSON array from a downstream request header, then filter it
  json_set_header_values "$.anthropic_beta" "anthropic-beta";
  json_keep_values "$.anthropic_beta" "computer-use-*" "context-management-*";
  json_filter_values "$.anthropic_beta" "context-1m-*";
}

• Supports a subset of object-path JSONPath expressions (e.g. $.a.b.c).
• json_set values support primitives (true, false, null, integers, strings) or expressions (like concat(...)).
• json_wrap_input_text converts a string field into an OpenAI Responses input message list, leaves missing or already-array values unchanged, and rejects other types.
• json_keep_values filters a JSON string array, keeping only values that match any pattern (allowlist). Use after json_set_header_values to restrict a header-sourced array to a known-safe set.
• json_filter_values filters a JSON string array, removing values that match any pattern (denylist).
• Both json_keep_values and json_filter_values support * wildcards, are case-insensitive, and delete the field if no values remain.

Structural Request Mapping

Use req_map to apply heavy, cross-provider schema transformations (such as converting an OpenAI JSON request into a Gemini or Anthropic JSON request).

request { req_map <mode>; }

Use after_req_map when a request JSON mutation must run after the structural mapping step.

request {
  req_map openai_chat_to_anthropic_messages;

  after_req_map {
    json_set "$.anthropic_version" "bedrock-2023-05-31";
    json_del_if_missing "$.tool_choice" "$.tools";
  }
}

• Only request JSON mutation directives are allowed inside after_req_map.
• If no req_map is configured, after_req_map runs after the normal request JSON operations.

Built-in Modes (v0.1)

• openai_chat_to_openai_responses
• anthropic_to_openai_chat
• gemini_to_openai_chat
• openai_chat_to_gemini_generate_content
• openai_chat_to_anthropic_messages