Blog
Mert Özen's blog posts on software development, backend, frontend, and DevOps.
Claude or ChatGPT? A Job-by-Job Comparison for Developers and Knowledge Workers
Choose between Claude and ChatGPT by the job and with your own task set, not by asking which is better; the business defaults and team plan prices of the two products are very close, and the real difference is between personal and business accounts. Concept mapping as of 15 November 2026, research, documents, files, browser and background work, portability with MCP and SKILL.md, a privacy and plan table, and a decision for the Bookstore team.
Privacy and Data Controls in ChatGPT: Model Training, Temporary Chat, Memory and Business Plans
On personal ChatGPT plans "Improve the model for everyone" is on by default, and turning it off only affects new chats; Business, Enterprise and Edu data is not used for training by default. The feedback and Daybreak exceptions, voice recordings, 30-day deletion, how Temporary Chat is kept, business boundaries, Space and dots as of 15 November 2026, a masking practice for KVKK and the rule list of Bookstore's support team.
Images and Voice in ChatGPT: Image Generation, Image Inputs and ChatGPT Voice
Use image generation in ChatGPT for ideas and drafts and image inputs to find where to look; do the measuring and the final diagram with code, and clean customer data out of screenshots. gpt-image-2 and Images 2.6 as of 15 November 2026, two different official statements about the Free plan, targeted edit prompts, an accessibility review of the basket screen, Live voice, the retirement of Advanced and Standard voice on 11 December 2026 and the cost of ChatGPT Voice on the desktop.
Space, Pages, Sites and Visualizations in ChatGPT: Documents and Sharing After Canvas
Canvas was replaced by writing blocks in the chat and by ChatGPT Space, which teams edit together; in Space linked files keep their own permissions, but content copied onto a page is visible to everyone who can see it. Pages and slides, inherited access, visualizations as snapshots, access options, limits and 2027 hosting prices of Sites in public beta as of 15 November 2026, and which job belongs where for Bookstore.
Big Tasks with ChatGPT Work: File Analysis, Document/Deck/Sheet Creation, Scheduled Tasks and Dots
When you give ChatGPT Work a big task, write the outcome, the constraints and the verification criteria, and ask for the plan first; refine the file with annotations and check the numbers against the source. Subagents, document/deck/sheet previews, scheduled tasks triggered by time or app events, dots access and custom rules as of 15 November 2026, and Bookstore's third-quarter sales CSV with a table of correct answers.
Web Search, Deep Research and Browser in ChatGPT: Cited Research and Getting Things Done on the Web
In ChatGPT, use web search for a single current fact, deep research in Work for a multi-source report and Browser for actions on a site; in all three, web content is untrusted input and a citation is an address, not evidence. Deep research drawing on Work usage and its editable plan as of 15 November 2026, permissions of the cloud browser, the built-in browser and the browser extension, sites that need a sign-in, and a source check table for Bookstore.
Plugins, Skills, Apps and MCP in ChatGPT: Moving from Custom GPTs to Plugins
Custom GPTs retire on 11 December 2026; when migrating to a plugin, instructions become a skill, knowledge files become reference files and connected apps move into the plugin, while custom actions, the selected model and sharing settings do not move. Plugin, skill and app concepts, plugins being limited to the user's existing access, remote MCP in ChatGPT on the web through plugins, and a plan to move Bookstore's quote GPT with an MCP plugin.
ChatGPT Projects: Keeping Sources, Project Instructions and Chats Together
In ChatGPT, open a project for work that continues over time, produces several outputs and relies on the same files, and start a separate chat inside it for each distinct output; one giant chat mixes old versions into answers. Chats, Sources and project instructions, the 5, 25 and 40 file limits by plan as of 15 November 2026, project-only memory, local projects on desktop, and a Bookstore product documentation project.
Personalizing ChatGPT: Custom Instructions, Base Style and Tone, Memories and Temporary Chat
In ChatGPT, personal preferences go into custom instructions and team rules into a project and AGENTS.md; memory is only a recall layer, and deleting a chat does not delete a saved memory. Base style and tone, the 1,500- and 5,000-character custom instructions as of 15 November 2026, the difference between ChatGPT and Codex memory, Computer History, Temporary Chat, and which rule goes where for the Bookstore team.
Choosing Models and Reasoning Effort in ChatGPT: GPT-6 Sol, Astra, Luna and Terra
The rule for choosing a model in ChatGPT is to start with the default effort and raise it only for multi-step work with trade-offs; the Thinking setting in Chat and the Power presets in Work and Codex are separate controls. The GPT-6 menu as of 15 November 2026, which jobs Astra, GPT-6.1 Sol, Terra and Luna suit, Max and Ultra, the GPT-5.5 retirement, and a method for comparing a Bookstore campaign analysis at two settings.
Getting Started with ChatGPT in 2026: Chat, ChatGPT Work and Codex Modes, Surfaces and Plans
In ChatGPT, use Chat for questions and short drafts, ChatGPT Work for a reviewable file or a multi-step result, and Codex for code and tests; Work and Codex share the same usage limit and credits. Cloud and local work, the web, desktop, mobile and Slack/Teams surfaces, the Free, Go, Plus, Pro, Business and Enterprise plans as of 15 November 2026, feature maturity labels, and choosing a mode for the Bookstore team.