diff --git a/.claude/settings.json b/.claude/settings.json
new file mode 100644
index 00000000..20a491c5
--- /dev/null
+++ b/.claude/settings.json
@@ -0,0 +1,10 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(mkdir -p /home/feyishola/Desktop/mydev/opensource/starkpulse-frontend/apps/backend/src/contributor-registry/dto)"
+    ],
+    "additionalDirectories": [
+      "/home/feyishola/Desktop/mydev/opensource/starkpulse-frontend/apps/backend/src/contributor-registry"
+    ]
+  }
+}
diff --git a/apps/backend/src/app.module.ts b/apps/backend/src/app.module.ts
index 01bd26d2..e58483ca 100644
--- a/apps/backend/src/app.module.ts
+++ b/apps/backend/src/app.module.ts
@@ -54,6 +54,7 @@ import { SignalsModule } from './signals/signals.module';
 import { AnalyticsModule } from './analytics/analytics.module';
 import { AppConfigModule } from './config/config.module';
 import { CrowdfundModule } from './crowdfund/crowdfund.module';
+import { ContributorRegistryModule } from './contributor-registry/contributor-registry.module';
 import { AuditModule } from './audit/audit.module';
 import { AuditLogInterceptor } from './audit/interceptors/audit-log.interceptor';
 import { SorobanEventsModule } from './soroban-events/soroban-events.module';
@@ -123,6 +124,7 @@ import { VestingWalletModule } from './vesting-wallet/vesting-wallet.module';
     SearchModule,
     FeatureFlagsModule,
     CrowdfundModule,
+    ContributorRegistryModule,
     AppConfigModule,
     AuditModule,
     SorobanEventsModule,
diff --git a/apps/backend/src/common/rate-limit/rate-limit.config.ts b/apps/backend/src/common/rate-limit/rate-limit.config.ts
index f86d0e62..aca2cf47 100644
--- a/apps/backend/src/common/rate-limit/rate-limit.config.ts
+++ b/apps/backend/src/common/rate-limit/rate-limit.config.ts
@@ -309,3 +309,15 @@ export function getAnalyticsReadThrottleOverride() {
     default: getRateLimitSettings().analyticsRead,
   };
 }
+
+export function getRegistryReadThrottleOverride() {
+  return {
+    default: getRateLimitSettings().crowdfundRead,
+  };
+}
+
+export function getRegistryWriteThrottleOverride() {
+  return {
+    default: getRateLimitSettings().portfolioWrite,
+  };
+}
diff --git a/apps/backend/src/contributor-registry/contributor-registry.controller.ts b/apps/backend/src/contributor-registry/contributor-registry.controller.ts
new file mode 100644
index 00000000..8b226b5a
--- /dev/null
+++ b/apps/backend/src/contributor-registry/contributor-registry.controller.ts
@@ -0,0 +1,144 @@
+import { Body, Controller, Get, Param, Post } from '@nestjs/common';
+import { ApiOperation, ApiParam, ApiResponse, ApiTags } from '@nestjs/swagger';
+import { Throttle } from '@nestjs/throttler';
+import {
+  getRegistryReadThrottleOverride,
+  getRegistryWriteThrottleOverride,
+} from '../common/rate-limit/rate-limit.config';
+import { ContributorRegistryService } from './contributor-registry.service';
+import {
+  ContributorResponseDto,
+  NonceResponseDto,
+  RegisterContributorDto,
+  RegisterWithSigDto,
+  RegistrationXdrResponseDto,
+  ReputationResponseDto,
+  SubmitResponseDto,
+} from './dto/contributor-registry.dto';
+
+@ApiTags('contributor-registry')
+@Controller('contributor-registry')
+export class ContributorRegistryController {
+  constructor(private readonly svc: ContributorRegistryService) {}
+
+  // ── Registration ──────────────────────────────────────────────────────────────
+
+  @Post('register')
+  @Throttle(getRegistryWriteThrottleOverride())
+  @ApiOperation({
+    summary: 'Register a contributor (direct)',
+    description:
+      'In mock mode: immediately stores the contributor and returns a placeholder XDR. ' +
+      'In real mode: builds an unsigned Soroban transaction XDR that the contributor ' +
+      'must sign with their Stellar wallet and submit independently.',
+  })
+  @ApiResponse({
+    status: 201,
+    description: 'Registration XDR built (or contributor stored in mock mode)',
+    type: RegistrationXdrResponseDto,
+  })
+  @ApiResponse({ status: 400, description: 'Contract not configured or invalid input' })
+  @ApiResponse({ status: 409, description: 'Contributor already registered or handle taken' })
+  register(@Body() dto: RegisterContributorDto): Promise<RegistrationXdrResponseDto> {
+    return this.svc.buildRegistrationXdr(dto);
+  }
+
+  @Post('register-with-sig')
+  @Throttle(getRegistryWriteThrottleOverride())
+  @ApiOperation({
+    summary: 'Gasless contributor registration (testnet signing + submission)',
+    description:
+      'The contributor signs a SorobanAuthorizationEntry off-chain (no XLM required). ' +
+      'The server (relayer) builds the transaction, attaches the signed entry, and ' +
+      'submits it — paying the network fees. ' +
+      'Obtain the current nonce first via GET /contributor-registry/nonce/:address.',
+  })
+  @ApiResponse({
+    status: 201,
+    description: 'Transaction submitted successfully',
+    type: SubmitResponseDto,
+  })
+  @ApiResponse({ status: 400, description: 'Invalid signed auth entry or contract not configured' })
+  @ApiResponse({ status: 409, description: 'Contributor already registered or handle taken' })
+  registerWithSig(@Body() dto: RegisterWithSigDto): Promise<SubmitResponseDto> {
+    return this.svc.registerWithSignature(dto);
+  }
+
+  // ── Lookups ───────────────────────────────────────────────────────────────────
+
+  @Get('wallet/:address')
+  @Throttle(getRegistryReadThrottleOverride())
+  @ApiOperation({
+    summary: 'Look up contributor by Stellar wallet address',
+    description: 'Returns contributor profile. Result is cached for 60 seconds.',
+  })
+  @ApiParam({ name: 'address', example: 'GABC1234...', description: 'Stellar public key (G...)' })
+  @ApiResponse({
+    status: 200,
+    description: 'Contributor profile',
+    type: ContributorResponseDto,
+  })
+  @ApiResponse({ status: 404, description: 'Contributor not found' })
+  getByAddress(@Param('address') address: string): Promise<ContributorResponseDto> {
+    return this.svc.getContributorByAddress(address);
+  }
+
+  @Get('github/:handle')
+  @Throttle(getRegistryReadThrottleOverride())
+  @ApiOperation({
+    summary: 'Look up contributor by GitHub handle',
+    description: 'Returns contributor profile. Result is cached for 60 seconds.',
+  })
+  @ApiParam({ name: 'handle', example: 'octocat', description: 'GitHub username' })
+  @ApiResponse({
+    status: 200,
+    description: 'Contributor profile',
+    type: ContributorResponseDto,
+  })
+  @ApiResponse({ status: 404, description: 'Contributor not found' })
+  getByGithub(@Param('handle') handle: string): Promise<ContributorResponseDto> {
+    return this.svc.getContributorByGithub(handle);
+  }
+
+  // ── Reputation ────────────────────────────────────────────────────────────────
+
+  @Get('reputation/:address')
+  @Throttle(getRegistryReadThrottleOverride())
+  @ApiOperation({
+    summary: 'Read contributor reputation score and tier',
+    description:
+      'Returns the on-chain reputation score and derived tier. ' +
+      'Result is cached for 60 seconds to reduce RPC load.',
+  })
+  @ApiParam({ name: 'address', example: 'GABC1234...', description: 'Stellar public key (G...)' })
+  @ApiResponse({
+    status: 200,
+    description: 'Reputation data',
+    type: ReputationResponseDto,
+  })
+  @ApiResponse({ status: 404, description: 'Contributor not found' })
+  getReputation(@Param('address') address: string): Promise<ReputationResponseDto> {
+    return this.svc.getReputation(address);
+  }
+
+  // ── Nonce ─────────────────────────────────────────────────────────────────────
+
+  @Get('nonce/:address')
+  @Throttle(getRegistryReadThrottleOverride())
+  @ApiOperation({
+    summary: 'Get registration nonce for off-chain signing',
+    description:
+      'Returns the current per-address nonce required when building the ' +
+      'SorobanAuthorizationEntry for register_contributor_with_sig. ' +
+      'Cached for 5 seconds only — always fetch immediately before signing.',
+  })
+  @ApiParam({ name: 'address', example: 'GABC1234...', description: 'Stellar public key (G...)' })
+  @ApiResponse({
+    status: 200,
+    description: 'Current nonce',
+    type: NonceResponseDto,
+  })
+  getNonce(@Param('address') address: string): Promise<NonceResponseDto> {
+    return this.svc.getNonce(address);
+  }
+}
diff --git a/apps/backend/src/contributor-registry/contributor-registry.module.ts b/apps/backend/src/contributor-registry/contributor-registry.module.ts
new file mode 100644
index 00000000..81316c6e
--- /dev/null
+++ b/apps/backend/src/contributor-registry/contributor-registry.module.ts
@@ -0,0 +1,13 @@
+import { Module } from '@nestjs/common';
+import { AppCacheModule } from '../cache/cache.module';
+import { StellarModule } from '../stellar/stellar.module';
+import { ContributorRegistryController } from './contributor-registry.controller';
+import { ContributorRegistryService } from './contributor-registry.service';
+
+@Module({
+  imports: [AppCacheModule, StellarModule],
+  controllers: [ContributorRegistryController],
+  providers: [ContributorRegistryService],
+  exports: [ContributorRegistryService],
+})
+export class ContributorRegistryModule {}
diff --git a/apps/backend/src/contributor-registry/contributor-registry.service.ts b/apps/backend/src/contributor-registry/contributor-registry.service.ts
new file mode 100644
index 00000000..c7ef98d1
--- /dev/null
+++ b/apps/backend/src/contributor-registry/contributor-registry.service.ts
@@ -0,0 +1,499 @@
+import {
+  BadRequestException,
+  ConflictException,
+  Injectable,
+  Logger,
+  NotFoundException,
+} from '@nestjs/common';
+import {
+  Address,
+  BASE_FEE,
+  Contract,
+  Keypair,
+  Networks,
+  TransactionBuilder,
+  nativeToScVal,
+  rpc,
+  scValToNative,
+  xdr,
+} from '@stellar/stellar-sdk';
+import {
+  SorobanRpcError,
+  SorobanErrorCode,
+} from '../stellar/services/soroban-rpc-client.service';
+import { CacheService } from '../cache/cache.service';
+import { config } from '../lib/config';
+import { SorobanRpcClientService } from '../stellar/services/soroban-rpc-client.service';
+import {
+  ContributorResponseDto,
+  NonceResponseDto,
+  RegisterContributorDto,
+  RegisterWithSigDto,
+  RegistrationXdrResponseDto,
+  ReputationResponseDto,
+  SubmitResponseDto,
+} from './dto/contributor-registry.dto';
+
+const CONTRIBUTOR_CACHE_TTL = 60_000; // 1 minute — profiles change infrequently
+const REPUTATION_CACHE_TTL = 60_000; // 1 minute — can change via on_notify but short enough
+const NONCE_CACHE_TTL = 5_000; // 5 seconds — time-sensitive for off-chain signing
+
+const CACHE_PREFIX_ADDRESS = 'contributor-registry:address';
+const CACHE_PREFIX_GITHUB = 'contributor-registry:github';
+const CACHE_PREFIX_REPUTATION = 'contributor-registry:reputation';
+const CACHE_PREFIX_NONCE = 'contributor-registry:nonce';
+
+interface MockContributor {
+  address: string;
+  githubHandle: string;
+  reputationScore: number;
+  registeredAt: string;
+}
+
+@Injectable()
+export class ContributorRegistryService {
+  private readonly logger = new Logger(ContributorRegistryService.name);
+
+  // In-memory store used when USE_MOCK_TRANSACTIONS=true (default in development)
+  private readonly mockContributors = new Map<string, MockContributor>();
+  private readonly mockGithubIndex = new Map<string, string>(); // lowercase handle → address
+  private readonly mockNonces = new Map<string, number>(); // address → nonce
+
+  constructor(
+    private readonly cacheService: CacheService,
+    private readonly sorobanRpcClient: SorobanRpcClientService,
+  ) {}
+
+  // ── Helpers ──────────────────────────────────────────────────────────────────
+
+  private get useMock(): boolean {
+    return config.featureFlags.useMockTransactions;
+  }
+
+  private get contractId(): string | null {
+    return config.stellar.contracts.contributorRegistry;
+  }
+
+  private get networkPassphrase(): string {
+    return config.stellar.network === 'mainnet' ? Networks.PUBLIC : Networks.TESTNET;
+  }
+
+  private tierFromScore(score: number): string {
+    if (score >= 100) return 'Core';
+    if (score >= 50) return 'Architect';
+    if (score >= 10) return 'Builder';
+    return 'Novice';
+  }
+
+  private requireContractId(): string {
+    const id = this.contractId;
+    if (!id) {
+      throw new BadRequestException(
+        'Contributor registry contract address is not configured (STELLAR_CONTRACT_CONTRIBUTOR_REGISTRY)',
+      );
+    }
+    return id;
+  }
+
+  private relayerKeypair(): Keypair {
+    return Keypair.fromSecret(config.stellar.serverSecret.reveal());
+  }
+
+  // ── Registration ─────────────────────────────────────────────────────────────
+
+  /**
+   * Direct registration — requires the contributor's own authorization.
+   *
+   * Mock mode: stores the contributor immediately and returns a placeholder XDR.
+   * Real mode: builds an unsigned Soroban transaction and returns the XDR for
+   * the contributor to sign with their Stellar wallet before submitting.
+   */
+  async buildRegistrationXdr(dto: RegisterContributorDto): Promise<RegistrationXdrResponseDto> {
+    if (this.useMock) {
+      return this.mockRegister(dto);
+    }
+
+    const contractId = this.requireContractId();
+    const account = await this.sorobanRpcClient.getAccount(dto.address);
+    const contract = new Contract(contractId);
+
+    const tx = new TransactionBuilder(account, {
+      fee: BASE_FEE,
+      networkPassphrase: this.networkPassphrase,
+    })
+      .addOperation(
+        contract.call(
+          'register_contributor',
+          new Address(dto.address).toScVal(),
+          nativeToScVal(dto.githubHandle, { type: 'string' }),
+        ),
+      )
+      .setTimeout(30)
+      .build();
+
+    const simulation = await this.sorobanRpcClient.simulateTransaction(tx);
+    const preparedTx = rpc.assembleTransaction(tx, simulation).build();
+
+    return {
+      unsignedXdr: preparedTx.toXDR(),
+      networkPassphrase: this.networkPassphrase,
+    };
+  }
+
+  /**
+   * Gasless / meta-transaction registration — server acts as the relayer.
+   *
+   * The contributor signs a SorobanAuthorizationEntry off-chain (no XLM needed).
+   * The server builds the transaction, attaches the signed entry, and submits
+   * using the relayer account (STELLAR_SERVER_SECRET) which pays the fees.
+   *
+   * Mock mode: stores the contributor immediately and returns a mock receipt.
+   */
+  async registerWithSignature(dto: RegisterWithSigDto): Promise<SubmitResponseDto> {
+    if (this.useMock) {
+      return this.mockRegisterWithSig(dto);
+    }
+
+    const contractId = this.requireContractId();
+    const relayer = this.relayerKeypair();
+    const relayerAccount = await this.sorobanRpcClient.getAccount(relayer.publicKey());
+    const contract = new Contract(contractId);
+
+    // The `signature` parameter is arbitrary bytes attached for auditability;
+    // the cryptographic proof lives in the SorobanAuthorizationEntry.
+    const signatureBytes = dto.signatureHex
+      ? Buffer.from(dto.signatureHex, 'hex')
+      : Buffer.alloc(64, 0);
+
+    const tx = new TransactionBuilder(relayerAccount, {
+      fee: BASE_FEE,
+      networkPassphrase: this.networkPassphrase,
+    })
+      .addOperation(
+        contract.call(
+          'register_contributor_with_sig',
+          nativeToScVal(dto.githubHandle, { type: 'string' }),
+          new Address(dto.address).toScVal(),
+          xdr.ScVal.scvBytes(signatureBytes),
+        ),
+      )
+      .setTimeout(30)
+      .build();
+
+    const simulation = await this.sorobanRpcClient.simulateTransaction(tx);
+
+    // Assemble (applies resource fee and simulation-derived soroban data)
+    const preparedTx = rpc.assembleTransaction(tx, simulation).build();
+
+    // Replace the simulation's unsigned auth entry with the contributor's signed one
+    const signedAuthEntry = xdr.SorobanAuthorizationEntry.fromXDR(
+      dto.signedAuthEntryXdr,
+      'base64',
+    );
+    preparedTx
+      .toEnvelope()
+      .v1()
+      .tx()
+      .operations()[0]
+      .body()
+      .invokeHostFunctionOp()
+      .auth([signedAuthEntry]);
+
+    // Relayer signs to authorize the fee payment
+    preparedTx.sign(relayer);
+
+    const result = await this.sorobanRpcClient.sendTransaction(preparedTx);
+
+    this.logger.log(
+      `Gasless registration submitted: address=${dto.address} handle=${dto.githubHandle} hash=${result.hash}`,
+    );
+
+    return {
+      transactionHash: result.hash,
+      status: result.status === 'PENDING' ? 'PENDING' : 'SUCCESS',
+    };
+  }
+
+  // ── Lookups ───────────────────────────────────────────────────────────────────
+
+  async getContributorByAddress(address: string): Promise<ContributorResponseDto> {
+    return this.cacheService.getOrSet(
+      `${CACHE_PREFIX_ADDRESS}:${address}`,
+      () => this.fetchContributorByAddress(address),
+      CONTRIBUTOR_CACHE_TTL,
+    );
+  }
+
+  async getContributorByGithub(githubHandle: string): Promise<ContributorResponseDto> {
+    return this.cacheService.getOrSet(
+      `${CACHE_PREFIX_GITHUB}:${githubHandle.toLowerCase()}`,
+      () => this.fetchContributorByGithub(githubHandle),
+      CONTRIBUTOR_CACHE_TTL,
+    );
+  }
+
+  // ── Reputation ────────────────────────────────────────────────────────────────
+
+  async getReputation(address: string): Promise<ReputationResponseDto> {
+    return this.cacheService.getOrSet(
+      `${CACHE_PREFIX_REPUTATION}:${address}`,
+      () => this.fetchReputation(address),
+      REPUTATION_CACHE_TTL,
+    );
+  }
+
+  // ── Nonce ─────────────────────────────────────────────────────────────────────
+
+  async getNonce(address: string): Promise<NonceResponseDto> {
+    const nonce = await this.cacheService.getOrSet(
+      `${CACHE_PREFIX_NONCE}:${address}`,
+      () => this.fetchNonce(address),
+      NONCE_CACHE_TTL,
+    );
+    return { address, nonce };
+  }
+
+  // ── Private mock implementations ──────────────────────────────────────────────
+
+  private mockRegister(dto: RegisterContributorDto): RegistrationXdrResponseDto {
+    if (this.mockContributors.has(dto.address)) {
+      throw new ConflictException(`Contributor ${dto.address} is already registered`);
+    }
+    if (this.mockGithubIndex.has(dto.githubHandle.toLowerCase())) {
+      throw new ConflictException(`GitHub handle '${dto.githubHandle}' is already taken`);
+    }
+
+    this.mockContributors.set(dto.address, {
+      address: dto.address,
+      githubHandle: dto.githubHandle,
+      reputationScore: 0,
+      registeredAt: new Date().toISOString(),
+    });
+    this.mockGithubIndex.set(dto.githubHandle.toLowerCase(), dto.address);
+
+    this.logger.log(`[mock] Registered contributor address=${dto.address} handle=${dto.githubHandle}`);
+
+    return {
+      unsignedXdr: 'MOCK_UNSIGNED_XDR',
+      networkPassphrase: this.networkPassphrase,
+    };
+  }
+
+  private mockRegisterWithSig(dto: RegisterWithSigDto): SubmitResponseDto {
+    if (this.mockContributors.has(dto.address)) {
+      throw new ConflictException(`Contributor ${dto.address} is already registered`);
+    }
+    if (this.mockGithubIndex.has(dto.githubHandle.toLowerCase())) {
+      throw new ConflictException(`GitHub handle '${dto.githubHandle}' is already taken`);
+    }
+
+    const nonce = this.mockNonces.get(dto.address) ?? 0;
+    this.mockContributors.set(dto.address, {
+      address: dto.address,
+      githubHandle: dto.githubHandle,
+      reputationScore: 0,
+      registeredAt: new Date().toISOString(),
+    });
+    this.mockGithubIndex.set(dto.githubHandle.toLowerCase(), dto.address);
+    this.mockNonces.set(dto.address, nonce + 1);
+
+    this.logger.log(
+      `[mock] Gasless-registered contributor address=${dto.address} handle=${dto.githubHandle}`,
+    );
+
+    return {
+      transactionHash: `mock_tx_${Date.now()}`,
+      status: 'SUCCESS',
+      ledger: Math.floor(Math.random() * 1_000_000) + 50_000_000,
+    };
+  }
+
+  // ── Private real-chain fetchers ────────────────────────────────────────────────
+
+  private async fetchContributorByAddress(address: string): Promise<ContributorResponseDto> {
+    if (this.useMock) {
+      const contributor = this.mockContributors.get(address);
+      if (!contributor) {
+        throw new NotFoundException(`Contributor with address ${address} not found`);
+      }
+      return { ...contributor, tier: this.tierFromScore(contributor.reputationScore) };
+    }
+
+    const contractId = this.requireContractId();
+    const relayer = this.relayerKeypair();
+    const account = await this.sorobanRpcClient.getAccount(relayer.publicKey());
+    const contract = new Contract(contractId);
+
+    const tx = new TransactionBuilder(account, {
+      fee: BASE_FEE,
+      networkPassphrase: this.networkPassphrase,
+    })
+      .addOperation(contract.call('get_contributor', new Address(address).toScVal()))
+      .setTimeout(30)
+      .build();
+
+    let simulation: rpc.Api.SimulateTransactionResponse;
+    try {
+      simulation = await this.sorobanRpcClient.simulateTransaction(tx);
+    } catch (err) {
+      if (err instanceof SorobanRpcError && err.code === SorobanErrorCode.SIMULATION_FAILED) {
+        throw new NotFoundException(`Contributor with address ${address} not found`);
+      }
+      throw err;
+    }
+
+    if (!simulation.result) {
+      throw new NotFoundException(`Contributor with address ${address} not found`);
+    }
+
+    return this.parseContributorData(simulation.result.retval);
+  }
+
+  private async fetchContributorByGithub(githubHandle: string): Promise<ContributorResponseDto> {
+    if (this.useMock) {
+      const address = this.mockGithubIndex.get(githubHandle.toLowerCase());
+      if (!address) {
+        throw new NotFoundException(`Contributor with GitHub handle '${githubHandle}' not found`);
+      }
+      // Re-use the address fetcher (no extra network call in mock mode)
+      return this.fetchContributorByAddress(address);
+    }
+
+    const contractId = this.requireContractId();
+    const relayer = this.relayerKeypair();
+    const account = await this.sorobanRpcClient.getAccount(relayer.publicKey());
+    const contract = new Contract(contractId);
+
+    const tx = new TransactionBuilder(account, {
+      fee: BASE_FEE,
+      networkPassphrase: this.networkPassphrase,
+    })
+      .addOperation(
+        contract.call(
+          'get_contributor_by_github',
+          nativeToScVal(githubHandle, { type: 'string' }),
+        ),
+      )
+      .setTimeout(30)
+      .build();
+
+    let simulation: rpc.Api.SimulateTransactionResponse;
+    try {
+      simulation = await this.sorobanRpcClient.simulateTransaction(tx);
+    } catch (err) {
+      if (err instanceof SorobanRpcError && err.code === SorobanErrorCode.SIMULATION_FAILED) {
+        throw new NotFoundException(`Contributor with GitHub handle '${githubHandle}' not found`);
+      }
+      throw err;
+    }
+
+    if (!simulation.result) {
+      throw new NotFoundException(`Contributor with GitHub handle '${githubHandle}' not found`);
+    }
+
+    return this.parseContributorData(simulation.result.retval);
+  }
+
+  private async fetchReputation(address: string): Promise<ReputationResponseDto> {
+    if (this.useMock) {
+      const contributor = this.mockContributors.get(address);
+      if (!contributor) {
+        throw new NotFoundException(`Contributor with address ${address} not found`);
+      }
+      return {
+        address,
+        reputationScore: contributor.reputationScore,
+        tier: this.tierFromScore(contributor.reputationScore),
+      };
+    }
+
+    const contractId = this.requireContractId();
+    const relayer = this.relayerKeypair();
+    const account = await this.sorobanRpcClient.getAccount(relayer.publicKey());
+    const contract = new Contract(contractId);
+
+    const tx = new TransactionBuilder(account, {
+      fee: BASE_FEE,
+      networkPassphrase: this.networkPassphrase,
+    })
+      .addOperation(contract.call('get_reputation', new Address(address).toScVal()))
+      .setTimeout(30)
+      .build();
+
+    let simulation: rpc.Api.SimulateTransactionResponse;
+    try {
+      simulation = await this.sorobanRpcClient.simulateTransaction(tx);
+    } catch (err) {
+      if (err instanceof SorobanRpcError && err.code === SorobanErrorCode.SIMULATION_FAILED) {
+        throw new NotFoundException(`Contributor with address ${address} not found`);
+      }
+      throw err;
+    }
+
+    if (!simulation.result) {
+      throw new NotFoundException(`Contributor with address ${address} not found`);
+    }
+
+    const score = Number(scValToNative(simulation.result.retval) as bigint);
+
+    return { address, reputationScore: score, tier: this.tierFromScore(score) };
+  }
+
+  private async fetchNonce(address: string): Promise<number> {
+    if (this.useMock) {
+      return this.mockNonces.get(address) ?? 0;
+    }
+
+    const contractId = this.contractId;
+    if (!contractId) {
+      return 0;
+    }
+
+    const relayer = this.relayerKeypair();
+    const account = await this.sorobanRpcClient.getAccount(relayer.publicKey());
+    const contract = new Contract(contractId);
+
+    const tx = new TransactionBuilder(account, {
+      fee: BASE_FEE,
+      networkPassphrase: this.networkPassphrase,
+    })
+      .addOperation(contract.call('get_registration_nonce', new Address(address).toScVal()))
+      .setTimeout(30)
+      .build();
+
+    try {
+      const simulation = await this.sorobanRpcClient.simulateTransaction(tx);
+
+      if (!rpc.Api.isSimulationSuccess(simulation) || !simulation.result) {
+        return 0;
+      }
+
+      return Number(scValToNative(simulation.result.retval) as bigint);
+    } catch {
+      // Not initialized or address has no nonce yet — safe default
+      return 0;
+    }
+  }
+
+  // ── XDR parsers ────────────────────────────────────────────────────────────────
+
+  private parseContributorData(retval: xdr.ScVal): ContributorResponseDto {
+    const data = scValToNative(retval) as {
+      address: string;
+      github_handle: string;
+      reputation_score: bigint;
+      registered_timestamp: bigint;
+    };
+
+    const score = Number(data.reputation_score);
+
+    return {
+      address: data.address,
+      githubHandle: data.github_handle,
+      reputationScore: score,
+      tier: this.tierFromScore(score),
+      // Soroban timestamps are Unix seconds; convert to ISO string
+      registeredAt: new Date(Number(data.registered_timestamp) * 1000).toISOString(),
+    };
+  }
+}
diff --git a/apps/backend/src/contributor-registry/dto/contributor-registry.dto.ts b/apps/backend/src/contributor-registry/dto/contributor-registry.dto.ts
new file mode 100644
index 00000000..8c8f6d6d
--- /dev/null
+++ b/apps/backend/src/contributor-registry/dto/contributor-registry.dto.ts
@@ -0,0 +1,132 @@
+import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
+import { IsNotEmpty, IsOptional, IsString, Matches } from 'class-validator';
+
+const GITHUB_HANDLE_PATTERN = /^[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,37}[a-zA-Z0-9])?$/;
+const GITHUB_HANDLE_MESSAGE =
+  'githubHandle must be a valid GitHub username (1-39 alphanumeric or hyphen characters, no leading/trailing hyphens)';
+
+export class RegisterContributorDto {
+  @ApiProperty({
+    example: 'GABC1234...',
+    description: 'Stellar public key of the contributor (G...)',
+  })
+  @IsString()
+  @IsNotEmpty()
+  address: string;
+
+  @ApiProperty({
+    example: 'octocat',
+    description: 'GitHub username of the contributor',
+  })
+  @IsString()
+  @IsNotEmpty()
+  @Matches(GITHUB_HANDLE_PATTERN, { message: GITHUB_HANDLE_MESSAGE })
+  githubHandle: string;
+}
+
+export class RegisterWithSigDto {
+  @ApiProperty({
+    example: 'GABC1234...',
+    description: 'Stellar public key of the contributor (G...)',
+  })
+  @IsString()
+  @IsNotEmpty()
+  address: string;
+
+  @ApiProperty({
+    example: 'octocat',
+    description: 'GitHub username of the contributor',
+  })
+  @IsString()
+  @IsNotEmpty()
+  @Matches(GITHUB_HANDLE_PATTERN, { message: GITHUB_HANDLE_MESSAGE })
+  githubHandle: string;
+
+  @ApiProperty({
+    description:
+      'Base64-encoded SorobanAuthorizationEntry signed by the contributor off-chain. ' +
+      'Must authorize register_contributor_with_sig(github_handle, address, nonce).',
+    example: 'AAAAAQAAAA...',
+  })
+  @IsString()
+  @IsNotEmpty()
+  signedAuthEntryXdr: string;
+
+  @ApiPropertyOptional({
+    description:
+      'Hex-encoded raw Ed25519 signature bytes to pass as the contract `signature` parameter. ' +
+      'Defaults to 64 zero bytes when omitted (the auth entry is the real proof).',
+    example: 'deadbeef...',
+  })
+  @IsString()
+  @IsOptional()
+  signatureHex?: string;
+}
+
+export class ContributorResponseDto {
+  @ApiProperty({ example: 'GABC1234...' })
+  address: string;
+
+  @ApiProperty({ example: 'octocat' })
+  githubHandle: string;
+
+  @ApiProperty({ example: 42 })
+  reputationScore: number;
+
+  @ApiProperty({ enum: ['Novice', 'Builder', 'Architect', 'Core'], example: 'Builder' })
+  tier: string;
+
+  @ApiProperty({ example: '2026-01-01T00:00:00.000Z' })
+  registeredAt: string;
+}
+
+export class ReputationResponseDto {
+  @ApiProperty({ example: 'GABC1234...' })
+  address: string;
+
+  @ApiProperty({ example: 42 })
+  reputationScore: number;
+
+  @ApiProperty({ enum: ['Novice', 'Builder', 'Architect', 'Core'], example: 'Builder' })
+  tier: string;
+}
+
+export class RegistrationXdrResponseDto {
+  @ApiProperty({
+    description:
+      'Base64-encoded unsigned transaction XDR. In mock mode this is a placeholder string; ' +
+      'in real mode sign this with the contributor wallet and submit via a Stellar-compatible client.',
+    example: 'AAAAAQAAAA...',
+  })
+  unsignedXdr: string;
+
+  @ApiProperty({
+    description: 'Network passphrase required when signing the transaction.',
+    example: 'Test SDF Network ; September 2015',
+  })
+  networkPassphrase: string;
+}
+
+export class SubmitResponseDto {
+  @ApiProperty({ example: 'abc123...' })
+  transactionHash: string;
+
+  @ApiProperty({ enum: ['SUCCESS', 'PENDING', 'ERROR'], example: 'SUCCESS' })
+  status: string;
+
+  @ApiPropertyOptional({ example: 50123456 })
+  ledger?: number;
+}
+
+export class NonceResponseDto {
+  @ApiProperty({ example: 'GABC1234...' })
+  address: string;
+
+  @ApiProperty({
+    description:
+      'Current registration nonce for the address. Include this value in the ' +
+      'SorobanAuthorizationEntry scope when signing register_contributor_with_sig.',
+    example: 0,
+  })
+  nonce: number;
+}
diff --git a/memory/MEMORY.md b/memory/MEMORY.md
new file mode 100644
index 00000000..641506d7
--- /dev/null
+++ b/memory/MEMORY.md
@@ -0,0 +1,3 @@
+# Memory Index
+
+- [Project: Contributor Registry API](project_contributor_registry.md) — Backend module wrapping Soroban contributor registry contract with mock+real paths, caching, and gasless registration
diff --git a/memory/project_contributor_registry.md b/memory/project_contributor_registry.md
new file mode 100644
index 00000000..b98bf886
--- /dev/null
+++ b/memory/project_contributor_registry.md
@@ -0,0 +1,30 @@
+---
+name: project-contributor-registry
+description: Backend contributor registry API — NestJS module wrapping the Soroban contributor_registry contract with mock + real paths, caching, and gasless registration
+metadata:
+  type: project
+---
+
+Added `apps/backend/src/contributor-registry/` module implementing the contributor registry backend API.
+
+**Files created:**
+- `dto/contributor-registry.dto.ts` — all request/response DTOs
+- `contributor-registry.service.ts` — service with mock (in-memory Map) and real (SorobanRpcClientService) paths
+- `contributor-registry.controller.ts` — HTTP routes
+- `contributor-registry.module.ts` — NestJS module (imports AppCacheModule + StellarModule)
+
+**Files modified:**
+- `app.module.ts` — registered ContributorRegistryModule
+- `common/rate-limit/rate-limit.config.ts` — added `getRegistryReadThrottleOverride()` (delegates to crowdfundRead) and `getRegistryWriteThrottleOverride()` (delegates to portfolioWrite)
+
+**Routes:**
+- `POST /contributor-registry/register` — direct registration; mock stores immediately, real returns unsigned XDR for client signing
+- `POST /contributor-registry/register-with-sig` — gasless registration; server as relayer attaches client's signed SorobanAuthorizationEntry and submits
+- `GET /contributor-registry/wallet/:address` — lookup by Stellar address (60s cache)
+- `GET /contributor-registry/github/:handle` — lookup by GitHub handle (60s cache)
+- `GET /contributor-registry/reputation/:address` — reputation score + tier (60s cache)
+- `GET /contributor-registry/nonce/:address` — registration nonce for off-chain signing (5s cache)
+
+**Why:** Mock mode is gated by `config.featureFlags.useMockTransactions` (env `USE_MOCK_TRANSACTIONS=true` is the default in dev). Real mode uses `STELLAR_CONTRACT_CONTRIBUTOR_REGISTRY` env var for contract ID.
+
+**How to apply:** When working on this module, note that node_modules are not installed locally — `tsc --noEmit` will show pre-existing errors for the whole project, not just these files. The pattern to verify correctness is code review, not compilation.