JSON Parse Error - Unterminated String on Write Tool

[JacquesvanWyk]

Description

Model: kimi-k2.5-free
Tool Affected: write (file write)
Error: JSON Parse error: Unterminated string
Summary
Large content strings (>4-5KB) with code blocks cause JSON parsing failures when using the write tool.
Reproduction

1. Attempt to write file with content containing:
   • Markdown with SQL code blocks (triple backticks)
   • Unicode box-drawing characters (│ ├ └)
   • Length > 4000 characters
2. JSON parser fails with "Error message: JSON Parse error: Unterminated string]"
   Suspected Causes

• String length exceeding parser buffer
• Improper escaping of nested quotes or backticks
• Multibyte character handling issues
  Workaround
  Split content into smaller chunks (<3KB each) or use edit tool for incremental writes.
  Environment
• Platform: darwin/macOS
• Working with: Technical documentation, SQL schemas, code examples

Plugins

No response

OpenCode version

1.1.40

Steps to reproduce

No response

Screenshot and/or share link

No response

Operating System

macOS Tahoe Version 26.2

Terminal

Ghostty

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Incomplete JSON when writing out files #5890: Incomplete JSON when writing out files - Reports similar JSON parsing errors with incomplete output when writing files
• Error Writing Large Files (at least with Kimi K2.5) #10967: Error Writing Large Files (at least with Kimi K2.5) - Specifically mentions Kimi K2.5 model with large file writes causing JSON parsing failures
• [BUG] openai/gpt-5.2-codex Error message: JSON Parse error: Unterminated string errors #10755: openai/gpt-5.2-codex 'Error message: JSON Parse error: Unterminated string' errors - Similar JSON parsing errors with unterminated strings during normal usage
• JSON Parse error: Unterminated string with openrouter/kimi-k2 #1278: JSON Parse error: Unterminated string with openrouter/kimi-k2 - Earlier report of the same unterminated string error with Kimi model

Feel free to ignore if none of these address your specific case.

[rekram1-node]

can u provide a prompt to reproduce?

[JacquesvanWyk]

can u provide a prompt to reproduce?

Looks like its when its trying large write

⚙ invalid [tool=write, error=Invalid input for tool write: JSON parsing failed: Text: {"content": "# TownHub - Multi-Town Community Platform\n## Technical Specification Document v1.0\n\n---\n\n## 1. EXECUTIVE SUMMARY\n\nProduct Name: TownHub\nPurpose: Hyperlocal platform connecting residents with local businesses, events, and community information across multiple towns.\nTarget Market: South African towns (initially), with global scalability potential.\nRevenue Model: Freemium SaaS (business subscriptions) + transaction fees + advertising\nTech Stack: Laravel API (Backend) + Nuxt.js (Web) + Flutter (Mobile)\n\n---\n\n## 2. USER PERSONAS & USER STORIES\n\n### 2.1 User Types\n\nType A: Resident (Free User)\n- Discovers local businesses, events, and community updates\n- Can browse, search, review, and engage\n- Can post classifieds (limited free listings)\n- Can RSVP to events\n- Can message businesses\n\nType B: Business Owner\n- Basic tier: Free limited listing\n- Premium tier: R299/month - enhanced profile, analytics, unlimited deals\n- Pro tier: R699/month - booking system, priority placement, customer messaging\n- Enterprise: R999/month - white-label, API access, dedicated support\n\nType C: Town Administrator\n- Manages town settings and content moderation\n- Can broadcast emergency notifications\n- Views town analytics\n- Approves/rejects business claims\n\nType D: Super Admin (Platform Owner)\n- Manages all towns\n- User management across platform\n- Revenue analytics\n- System configuration\n\n### 2.2 Detailed User Stories\n\nAs a Resident:\n1. I want to join my town so I can see local content\n2. I want to search for businesses by category and location\n3. I want to view business details including hours, photos, and reviews\n4. I want to leave reviews and ratings for businesses I've visited\n5. I want to see upcoming events in my town and RSVP\n6. I want to buy/sell items locally through classifieds\n7. I want to receive notifications for events I'm attending\n8. I want to save businesses to favorites\n9. I want to share business listings via WhatsApp/SMS\n10. I want to see which businesses are currently open\n\nAs a Business Owner:\n1. I want to claim my business listing\n2. I want to update my business profile with photos, hours, description\n3. I want to create and manage deals/offers\n4. I want to post events to promote to the community\n5. I want to respond to customer reviews\n6. I want to see analytics on profile views and engagement\n7. I want to receive messages from potential customers\n8. I want to manage my subscription and billing\n9. I want to export customer data (with permissions)\n10. I want to integrate booking/appointment scheduling\n\nAs a Town Admin:\n1. I want to moderate community posts and remove inappropriate content\n2. I want to send broadcast notifications to all residents\n3. I want to approve business registrations in my town\n4. I want to view engagement metrics for my town\n5. I want to feature specific businesses or events\n6. I want to configure town-specific settings (categories, rules)\n7. I want to manage town residents and ban problematic users\n8. I want to export town analytics reports\n\n---\n\n## 3. DETAILED FEATURE SPECIFICATIONS\n\n### 3.1 AUTHENTICATION & USER MANAGEMENT\n\n3.1.1 Authentication System\n- Email/password registration with verification\n- Social login: Google, Facebook, Apple\n- Phone number verification (OTP via SMS)\n- JWT token-based authentication (Sanctum)\n- Password reset via email\n- Session management with refresh tokens\n- Rate limiting on login attempts (5 attempts per 15 minutes)\n\n3.1.2 User Profiles\nFields:\n- id (UUID)\n- email (unique, required)\n- phone_number (unique, optional)\n- first_name (required)\n- last_name (required)\n- avatar_url (nullable)\n- bio (text, max 500 chars, nullable)\n- date_of_birth (nullable)\n- gender (enum: male, female, other, prefer_not_to_say, nullable)\n- town_ids (array, many-to-many)\n- current_town_id (FK, nullable)\n- user_type (enum: resident, business_owner, town_admin, super_admin)\n- is_verified (boolean, default: false)\n- email_verified_at (timestamp)\n- phone_verified_at (timestamp)\n- notification_preferences (JSON)\n- privacy_settings (JSON)\n- created_at, updated_at, deleted_at\n\n3.1.3 User Roles & Permissions\nRoles:\n- resident: Basic browsing and engagement\n- business_owner: Can manage owned businesses\n- town_admin: Can moderate content in assigned towns\n- super_admin: Full platform access\n\nPermissions implemented via Laravel Spatie or custom middleware:\n- view_businesses\n- create_business\n- edit_own_business\n- delete_own_business\n- post_classified\n- create_event\n- moderate_content\n- broadcast_notifications\n- view_analytics\n- manage_subscriptions\n\n### 3.2 TOWN MANAGEMENT\n\n3.2.1 Town Entity\nFields:\n- id (UUID)\n- name (required, unique per country)\n- slug (required, URL-friendly)\n- description (text)\n- country (required, default: ZA)\n- province (required for SA)\n- city/town classification\n- latitude, longitude (for geofencing)\n- radius_km (service area radius)\n- cover_image_url\n- logo_url\n- primary_color, secondary_color (for branding)\n- timezone (default: Africa/Johannesburg)\n- currency (default: ZAR)\n- is_active (boolean)\n- is_featured (boolean)\n- settings (JSON: moderation_rules, posting_limits, etc.)\n- created_by (FK to users)\n- created_at, updated_at\n\n3.2.2 User-Town Relationship\nTable: user_town_memberships\n- id\n- user_id (FK)\n- town_id (FK)\n- role (enum: member, moderator, admin)\n- joined_at (timestamp)\n- is_primary (boolean)\n- notification_enabled (boolean)\n\n3.2.3 Town Joining Logic\n- Users can join multiple towns\n- User selects primary town (default view)\n- Can switch towns via town selector\n- Can discover nearby towns via geolocation\n- Must be approved to join private towns (rare)\n\n### 3.3 BUSINESS DIRECTORY\n\n3.3.1 Business Entity\nFields:\n- id (UUID)\n- name (required, max 255)\n- slug (required, unique per town)\n- description (text, max 5000)\n- short_description (text, max 160, for SEO)\n- town_id (FK, required)\n- owner_user_id (FK, nullable until claimed)\n- category_id (FK, required)\n- subcategory_ids (array of FKs)\n- status (enum: pending, active, suspended, closed)\n- verification_status (enum: unclaimed, pending, verified, rejected)\n\nContact Information:\n- phone_number (required)\n- whatsapp_number (nullable)\n- email (required)\n- website_url (nullable)\n- social_links (JSON: facebook, instagram, twitter, linkedin, tiktok)\n\nLocation:\n- address_line_1 (required)\n- address_line_2 (nullable)\n- suburb (required)\n- postal_code (required)\n- latitude (required)\n- longitude (required)\n- google_place_id (nullable)\n\nBusiness Details:\n- business_type (enum: physical, online, both)\n- year_established (nullable)\n- employee_count (enum: solo, 2-5, 6-10, 11-25, 26-50, 50+)\n- tags (array of strings, max 10)\n\nMedia:\n- logo_url (nullable)\n- cover_image_url (nullable)\n- gallery_images (array of URLs, max 20)\n-.
Error message: JSON Parse error: Unterminated string]

[shmish111]

I had this issue and it's a real PITA because everything stops and it seems opencode doesn't realise. If I tell it the error and tell it to use a sub agent then it will eventually work. I assume it sees the error output from the sub agent but not from itself.

[rekram1-node]

make sure you are on latest, if you installed via brew make sure you are using correct tap:
brew install anomalyco/tap/opencode

This was fixed in 1.1.41

[qingmo]

make sure you are on latest, if you installed via brew make sure you are using correct tap: brew install anomalyco/tap/opencode

This was fixed in 1.1.41

brew info opencode
==> opencode ✔: stable 1.1.50 (bottled)
the problem still appeared when write into file with a large content which are produced by ai model.

temp solution
⚙ invalid [tool=write, error=Invalid input for tool write: JSON parsing failed: Text: {"filePath": "xxxx.md".
Error message: JSON Parse error: Expected '}']
▣ Build · claude-sonnet · 2m 39s
Promot:Do not write all at once; write in batches to avoid writing issues.
it works