Codestral fill-in-the-middle completion

Instructions

Implementation Reference

• src/tools-fn.ts:174-238 (registration)

  Registration of the 'codestral_fim' tool via server.registerTool(). Defines metadata, inputSchema, outputSchema, and the handler callback.

  // ========== codestral_fim ==========
  server.registerTool(
    "codestral_fim",
    {
      title: "Codestral fill-in-the-middle completion",
      description: [
        "Fill-in-the-middle code completion with Codestral.",
        "",
        "Given `prompt` (code preceding the cursor) and `suffix` (code after the cursor),",
        "Codestral writes the middle. Use for editor autocomplete scenarios, code-patching",
        "agents, or structured refactors where you know the target boundaries.",
        "",
        "Default stop tokens: [] — let the model decide. Override with `stop` if needed.",
      ].join("\n"),
      inputSchema: {
        prompt: z.string().min(1).describe("Code preceding the cursor."),
        suffix: z.string().describe("Code after the cursor. Can be empty string."),
        model: FimModelSchema.optional(),
        stop: z.array(z.string()).optional(),
        ...ChatSamplingParams,
      },
      outputSchema: FimOutputShape,
      annotations: {
        title: "Codestral FIM",
        readOnlyHint: true,
        destructiveHint: false,
        idempotentHint: false,
        openWorldHint: true,
      },
    },
    async (input) => {
      try {
        const model = input.model ?? DEFAULT_FIM_MODEL;
        const res = await mistral.fim.complete({
          model,
          prompt: input.prompt,
          suffix: input.suffix,
          temperature: input.temperature,
          maxTokens: input.max_tokens,
          topP: input.top_p,
          randomSeed: input.seed,
          stop: input.stop,
        });
  
        const choice = res.choices?.[0];
        const content = choice?.message?.content ?? "";
        const text =
          typeof content === "string" ? content : JSON.stringify(content);
  
        const structured = {
          text,
          model,
          finish_reason: choice?.finishReason ?? undefined,
          usage: mapUsage(res.usage),
        };
  
        return {
          content: [toTextBlock(text)],
          structuredContent: structured,
        };
      } catch (err) {
        return errorResult("codestral_fim", err);
      }
    }
  );

• src/tools-fn.ts:69-74 (schema)

  Output shape for FIM: text, model, finish_reason, usage.

  export const FimOutputShape = {
    text: z.string(),
    model: z.string(),
    finish_reason: z.string().optional(),
    usage: UsageSchema.optional(),
  };

• src/tools-fn.ts:204-238 (handler)

  Handler function for codestral_fim: calls mistral.fim.complete() with prompt/suffix/model/params, extracts content, returns structured result.

    async (input) => {
      try {
        const model = input.model ?? DEFAULT_FIM_MODEL;
        const res = await mistral.fim.complete({
          model,
          prompt: input.prompt,
          suffix: input.suffix,
          temperature: input.temperature,
          maxTokens: input.max_tokens,
          topP: input.top_p,
          randomSeed: input.seed,
          stop: input.stop,
        });
  
        const choice = res.choices?.[0];
        const content = choice?.message?.content ?? "";
        const text =
          typeof content === "string" ? content : JSON.stringify(content);
  
        const structured = {
          text,
          model,
          finish_reason: choice?.finishReason ?? undefined,
          usage: mapUsage(res.usage),
        };
  
        return {
          content: [toTextBlock(text)],
          structuredContent: structured,
        };
      } catch (err) {
        return errorResult("codestral_fim", err);
      }
    }
  );

• src/shared.ts:97-103 (helper)

  errorResult helper: wraps errors into MCP error response format with tool name prefix.

  export function errorResult(tool: string, err: unknown) {
    const message = err instanceof Error ? err.message : String(err);
    return {
      content: [toTextBlock(`[mistral-mcp:${tool}] ${message}`)],
      isError: true as const,
    };
  }

• src/shared.ts:114-125 (helper)

  ChatSamplingParams: shared Zod schema for temperature/max_tokens/top_p/seed used in the FIM tool's inputSchema.

  export const ChatSamplingParams = {
    temperature: z.number().min(0).max(2).optional(),
    max_tokens: z.number().int().positive().optional(),
    top_p: z.number().min(0).max(1).optional(),
    seed: z
      .number()
      .int()
      .optional()
      .describe(
        "Random seed for deterministic sampling. Maps to Mistral's `random_seed`."
      ),
  };