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Gemini to Anthropic API Converter

Paste a Google Gemini generateContent request or response and get the equivalent Anthropic Messages JSON, systemInstruction, functionCall, finishReason and usageMetadatamapped field by field into Claude's system / messages / content-block shape. Runs entirely in your browser: no key, no upload, no signup.

By Induwara AshinsanaUpdated Jul 12, 2026
Convert a Gemini requestto Anthropic Messages
Payload type

Paste a Gemini request body. It is parsed in your browser, nothing is uploaded.

Written to the Anthropic model field. Confirm the tier fits your use case.

Used only when Gemini maxOutputTokens is absent, Anthropic requires max_tokens.

Output format
Messages
3
Fields mapped
6
Tool blocks
1
Notes / warnings
0
Converted Anthropic Messages request
{
  "model": "claude-sonnet-4-6",
  "system": "You are terse.",
  "messages": [
    {
      "role": "user",
      "content": [
        {
          "type": "text",
          "text": "Weather in Colombo?"
        }
      ]
    },
    {
      "role": "assistant",
      "content": [
        {
          "type": "tool_use",
          "id": "toolu_0",
          "name": "get_weather",
          "input": {
            "city": "Colombo"
          }
        }
      ]
    },
    {
      "role": "user",
      "content": [
        {
          "type": "tool_result",
          "tool_use_id": "toolu_0",
          "content": "{\"tempC\":31}"
        }
      ]
    }
  ],
  "max_tokens": 1024,
  "top_k": 40,
  "tools": [
    {
      "name": "get_weather",
      "description": "Get weather",
      "input_schema": {
        "type": "object",
        "properties": {
          "city": {
            "type": "string"
          }
        },
        "required": [
          "city"
        ]
      }
    }
  ]
}

Field-by-field mapping

GeminiAnthropicStatusDetail
—model: claude-sonnet-4-6MappedYou pick the target Claude model; Gemini requests have no model in the body.
systemInstructionsystem (top-level string)HoistedJoined part text into Anthropic's top-level system field (not a message).
contentsmessagesRenamedrole:"model" → "assistant"; each part → a content block (text / image / tool_use / tool_result).
tools[].functionDeclarations[]tools[]Renamedparameters → input_schema; name + description kept at the tool top level.
generationConfig.maxOutputTokens: 1024max_tokens: 1024RenamedCarried over, Anthropic requires max_tokens on every request.
generationConfig.topK: 40top_k: 40Renamed1:1, Anthropic supports top_k sampling.

Mapping follows the official Google Gemini generateContent and Anthropic Messages references, sources are listed below the tool. The converted request targets https://api.anthropic.com/v1/messages (header anthropic-version: 2023-06-01).

How it works

The converter is a deterministic transformation of a published schema. There is no model call. It reads your Gemini generateContent payload, applies a fixed set of rules transcribed from the official Google and Anthropic API references, and emits the equivalent Anthropic Messages JSON. Every rule is a static mapping, so the same input always produces the same output, and three worked examples are reconciled field-by-field on every load.

Requests are rebuilt turn by turn:

  1. System prompt. The top-level systemInstruction.parts[].text is hoisted into Anthropic's top-level system string. Unlike OpenAI, Claude keeps the system prompt outside the messages array.
  2. contents → messages. Order is preserved. role:"model" becomes assistant; user stays user. Every message's content is an array of blocks: a text part becomes {type:"text"} and an inlineData part becomes {type:"image",source:{type:"base64"}}.
  3. functionCall → tool_use. A model functionCall{name,args} becomes an assistant {type:"tool_use",id,name,input} block. The args object stays a JSON object in input, Claude does not stringify arguments. Gemini calls carry no id, so a stable toolu_0, toolu_1… is synthesized in order.
  4. functionResponse → tool_result. A user-turn functionResponse{name,response} becomes a {type:"tool_result",tool_use_id,content} block inside a user message, linked back to the matching synthesized tool_use id.
  5. tools & toolConfig. tools[].functionDeclarations[] becomes tools[] with parameters moved to input_schema (upper-case Type enums like STRING are lower-cased to JSON Schema). functionCallingConfig.mode: AUTO→{type:"auto"}, ANY→{type:"any"} (or {type:"tool",name} for one allowed function), NONE→{type:"none"}.
  6. generationConfig. maxOutputTokens → max_tokens (injected from the fallback box when absent, because Anthropic requires it), temperature → temperature(clamped to 1.0, Anthropic's maximum), topP → top_p, topK → top_k (1:1, Claude supports top-k, unlike OpenAI), and stopSequences → stop_sequences.

Responses wrap candidates[0] into a Messages object: {type:"message",role:"assistant",content,stop_reason,stop_sequence,usage}. Part text becomes {type:"text"} blocks, functionCall parts become tool_use blocks, and finishReason maps to stop_reason (STOP→end_turn, MAX_TOKENS→max_tokens; forced tool_use when a tool_use block is present; SAFETY/RECITATION→end_turn, flagged). usageMetadata maps to usage, promptTokenCount→input_tokens, candidatesTokenCount→output_tokens. Fields with no clean target, totalTokenCount, responseSchema, safetySettings, extra candidates, cachedContent, are listed in the notes panel, never silently dropped.

Worked examples

1, request with a tool call and tool response

  1. In: systemInstruction {"parts":[{"text":"You are terse."}]},
  2. contents: user "Weather in Colombo?",
  3. model functionCall get_weather{"city":"Colombo"},
  4. user functionResponse get_weather{"tempC":31},
  5. tools: get_weather, generationConfig {"maxOutputTokens":1024,"topK":40}
  6. —
  7. Out: model "claude-sonnet-4-6", system "You are terse.",
  8. max_tokens 1024, top_k 40,
  9. messages:[{"role":"user","content":[{"type":"text","text":"Weather in Colombo?"}]},
  10. {"role":"assistant","content":[{"type":"tool_use","id":"toolu_0",
  11. "name":"get_weather","input":{"city":"Colombo"}}]},
  12. {"role":"user","content":[{"type":"tool_result","tool_use_id":"toolu_0",
  13. "content":"{\"tempC\":31}"}]}]
  14. tools:[{"name":"get_weather","input_schema":{...}}]
  15. Check: input stays an OBJECT (not stringified); toolu_0 links result to call.

2, response mapping (MAX_TOKENS → max_tokens)

  1. In: candidates:[{"content":{"role":"model",
  2. "parts":[{"text":"It is 31°C in Colombo."}]},
  3. "finishReason":"MAX_TOKENS","index":0}],
  4. usageMetadata {"promptTokenCount":18,"candidatesTokenCount":9,
  5. "totalTokenCount":27}, modelVersion "gemini-2.5-flash"
  6. —
  7. Out: {"type":"message","role":"assistant","model":"gemini-2.5-flash",
  8. "content":[{"type":"text","text":"It is 31°C in Colombo."}],
  9. "stop_reason":"max_tokens","stop_sequence":null,
  10. "usage":{"input_tokens":18,"output_tokens":9}}
  11. Check: MAX_TOKENS → max_tokens; totalTokenCount 27 surfaced as a note
  12. (Anthropic has no total_tokens field); modelVersion → model.

3, edge cases (handled deliberately, no crash)

  1. Non-object input (array / "hi" / null) → a friendly, specific error, no output.
  2. maxOutputTokens absent → max_tokens injected from the fallback box (flagged Required-now).
  3. temperature 1.5 → clamped to 1.0 (Anthropic max), flagged Range-changed.
  4. functionResponse with no preceding functionCall → a fresh toolu_N id + a flag.
  5. Uppercase parameter Type enums (STRING, OBJECT) → lower-cased JSON Schema + a flag.
  6. candidateCount 3 → only candidates[0] converts; the extra 2 are flagged, not dropped silently.

Frequently asked questions

Sources & references

The mapping rules were last cross-checked against the official Gemini and Anthropic references on 2026-07-12. This page is reviewed whenever either provider ships a breaking request- or response-schema change.

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Comments & feedback

Spotted a bug or want an improvement? Tell us, our team reviews every comment, and good ideas get built. Comments are public and anonymous.

Found a field that maps wrong, or want another provider pair added?

Email me at [email protected] , most fixes ship within 24 hours.