diff --git a/packages/hydrojudge/src/check.ts b/packages/hydrojudge/src/check.ts
deleted file mode 100644
index 1223c6dab..000000000
--- a/packages/hydrojudge/src/check.ts
+++ /dev/null
@@ -1,35 +0,0 @@
-import { findFileSync } from '@hydrooj/utils/lib/utils';
-import checkers from './checkers';
-import compile from './compile';
-import { SystemError } from './error';
-import { CheckConfig, Execute } from './interface';
-
-const testlibSrc = findFileSync('@hydrooj/hydrojudge/vendor/testlib/testlib.h');
-
-export async function check(config: CheckConfig): Promise<[number, number, string]> {
-    if (!checkers[config.checker_type]) throw new SystemError('Unknown checker type {0}', [config.checker_type]);
-    const {
-        code, status, score, message,
-    } = await checkers[config.checker_type](config);
-    if (code) throw new SystemError('Checker returned {0}.', [code]);
-    return [status, score, message];
-}
-
-export async function compileChecker(getLang: Function, checkerType: string, checker: string, copyIn: any): Promise<Execute> {
-    if (['default', 'strict'].includes(checkerType)) {
-        return { execute: '', copyIn: {}, clean: () => Promise.resolve(null) };
-    }
-    if (!checkers[checkerType]) throw new SystemError('Unknown checker type {0}.', [checkerType]);
-    if (checkerType === 'testlib') copyIn['testlib.h'] = { src: testlibSrc };
-    const s = checker.replace('@', '.').split('.');
-    let lang;
-    let langId = s.pop();
-    while (s.length) {
-        lang = getLang(langId, false);
-        if (lang) break;
-        langId = `${s.pop()}.${langId}`;
-    }
-    if (!lang) throw new SystemError('Unknown checker language.');
-    // TODO cache compiled checker
-    return await compile(lang, { src: checker }, copyIn);
-}
diff --git a/packages/hydrojudge/src/checkers.ts b/packages/hydrojudge/src/checkers.ts
index 91bca0cd4..9cb9a3c24 100644
--- a/packages/hydrojudge/src/checkers.ts
+++ b/packages/hydrojudge/src/checkers.ts
@@ -1,6 +1,6 @@
 /* eslint-disable no-template-curly-in-string */
 import { STATUS } from '@hydrooj/utils/lib/status';
-import { SystemError } from './error';
+import { FormatError, SystemError } from './error';
 import { CheckConfig } from './interface';
 import { run } from './sandbox';
 import { parse } from './testlib';
@@ -9,10 +9,9 @@ type Checker = (config: CheckConfig) => Promise<{
     status: number,
     score: number,
     message: string,
-    code?: number,
 }>;
 
-const checkers: Record<string, Checker> = {
+const checkers: Record<string, Checker> = new Proxy({
     async default(config) {
         const { stdout } = await run('/usr/bin/diff -BZ usrout answer', {
             copyIn: {
@@ -196,6 +195,11 @@ const checkers: Record<string, Checker> = {
         }
         return parse(stderr, config.score);
     },
-};
+}, {
+    get(self, key) {
+        if (!self[key]) throw new FormatError('Unknown checker type {0}', [key]);
+        return self[key];
+    },
+});
 
 export = checkers;
diff --git a/packages/hydrojudge/src/compile.ts b/packages/hydrojudge/src/compile.ts
index 679461917..669cceb05 100644
--- a/packages/hydrojudge/src/compile.ts
+++ b/packages/hydrojudge/src/compile.ts
@@ -1,11 +1,13 @@
 import { LangConfig } from '@hydrooj/utils/lib/lang';
 import { STATUS } from '@hydrooj/utils/lib/status';
-import { CompileError } from './error';
+import { findFileSync } from '@hydrooj/utils/lib/utils';
+import checkers from './checkers';
+import { CompileError, FormatError } from './error';
 import { Execute } from './interface';
 import { CopyInFile, del, run } from './sandbox';
 import { compilerText } from './utils';
 
-export = async function compile(
+export default async function compile(
     lang: LangConfig, code: CopyInFile, copyIn: Record<string, CopyInFile> = {}, next?: Function,
 ): Promise<Execute> {
     const target = lang.target || 'foo';
@@ -24,7 +26,7 @@ export = async function compile(
         );
         if (status !== STATUS.STATUS_ACCEPTED) throw new CompileError({ status, stdout, stderr });
         if (!fileIds[target]) throw new CompileError({ stderr: 'Executable file not found.' });
-        if (next) next({ compilerText: compilerText(stdout, stderr) });
+        next?.({ compilerText: compilerText(stdout, stderr) });
         return {
             execute,
             copyIn: { ...copyIn, [target]: { fileId: fileIds[target] } },
@@ -38,4 +40,25 @@ export = async function compile(
         clean: () => Promise.resolve(null),
         time,
     };
-};
+}
+
+const testlibSrc = findFileSync('@hydrooj/hydrojudge/vendor/testlib/testlib.h');
+
+export async function compileChecker(getLang: Function, checkerType: string, checker: string, copyIn: any): Promise<Execute> {
+    if (['default', 'strict'].includes(checkerType)) {
+        return { execute: '', copyIn: {}, clean: () => Promise.resolve(null) };
+    }
+    if (!checkers[checkerType]) throw new FormatError('Unknown checker type {0}.', [checkerType]);
+    if (checkerType === 'testlib') copyIn['testlib.h'] = { src: testlibSrc };
+    const s = checker.replace('@', '.').split('.');
+    let lang;
+    let langId = s.pop();
+    while (s.length) {
+        lang = getLang(langId, false);
+        if (lang) break;
+        langId = `${s.pop()}.${langId}`;
+    }
+    if (!lang) throw new FormatError('Unknown checker language.');
+    // TODO cache compiled checker
+    return await compile(lang, { src: checker }, copyIn);
+}
diff --git a/packages/hydrojudge/src/interface.ts b/packages/hydrojudge/src/interface.ts
index 1014c4c15..a9f4ce2b4 100644
--- a/packages/hydrojudge/src/interface.ts
+++ b/packages/hydrojudge/src/interface.ts
@@ -9,7 +9,6 @@ export interface Execute {
 
 export interface CheckConfig {
     execute: string;
-    checker_type: string;
     input: CopyInFile;
     output: CopyInFile;
     user_stdout: CopyInFile;
diff --git a/packages/hydrojudge/src/judge/default.ts b/packages/hydrojudge/src/judge/default.ts
index ca55dd038..e570b643e 100644
--- a/packages/hydrojudge/src/judge/default.ts
+++ b/packages/hydrojudge/src/judge/default.ts
@@ -1,7 +1,7 @@
 import { basename } from 'path';
 import { STATUS } from '@hydrooj/utils/lib/status';
-import { check, compileChecker } from '../check';
-import compile from '../compile';
+import checkers from '../checkers';
+import compile, { compileChecker } from '../compile';
 import { runFlow } from '../flow';
 import { Logger } from '../log';
 import { CmdFile, del, run } from '../sandbox';
@@ -48,18 +48,17 @@ function judgeCase(c: NormalizedCase, sid: string) {
             } else if (memory_usage_kb > c.memory * 1024) {
                 status = STATUS.STATUS_MEMORY_LIMIT_EXCEEDED;
             } else {
-                [status, score, message] = await check({
+                ({ status, score, message } = await checkers[ctx.config.checker_type]({
                     execute: ctx.checker.execute,
                     copyIn: ctx.checker.copyIn || {},
                     input: { src: c.input },
                     output: { src: c.output },
                     user_stdout: stdout,
                     user_stderr: stderr,
-                    checker_type: ctx.config.checker_type,
                     score: c.score,
                     detail: ctx.config.detail ?? true,
                     env: { ...ctx.env, HYDRO_TESTCASE: c.id.toString() },
-                });
+                }));
             }
         } else if (status === STATUS.STATUS_RUNTIME_ERROR && code) {
             if (code < 32) message = signals[code];
diff --git a/packages/hydrojudge/src/judge/submit_answer.ts b/packages/hydrojudge/src/judge/submit_answer.ts
index 1b1fb7a54..29b51cb57 100644
--- a/packages/hydrojudge/src/judge/submit_answer.ts
+++ b/packages/hydrojudge/src/judge/submit_answer.ts
@@ -1,7 +1,8 @@
 import { basename } from 'path';
 import { readFile } from 'fs-extra';
 import { STATUS } from '@hydrooj/utils/lib/status';
-import { check, compileChecker } from '../check';
+import checkers from '../checkers';
+import { compileChecker } from '../compile';
 import { runFlow } from '../flow';
 import { del, run } from '../sandbox';
 import { NormalizedCase } from '../utils';
@@ -47,18 +48,17 @@ function judgeCase(c: NormalizedCase, sid: string) {
             fileIds.push(...Object.values(res.fileIds));
         }
         if (status === STATUS.STATUS_ACCEPTED) {
-            [status, score, message] = await check({
+            ({ status, score, message } = await checkers[ctx.config.checker_type]({
                 execute: ctx.checker.execute,
                 copyIn: ctx.checker.copyIn || {},
                 input: { src: c.input },
                 output: { src: c.output },
                 user_stdout: file,
                 user_stderr: { content: '' },
-                checker_type: ctx.config.checker_type,
                 score: c.score,
                 detail: ctx.config.detail ?? true,
                 env: { ...ctx.env, HYDRO_TESTCASE: c.id.toString() },
-            });
+            }));
         }
         await Promise.all(fileIds.map(del)).catch(() => { /* Ignore file doesn't exist */ });
         ctxSubtask.score = Score[ctxSubtask.subtask.type](ctxSubtask.score, score);