Some AI coding agents load project-specific instructions before handling your first request so they can work with the repository’s conventions and workflows in mind. That does not usually mean they have read the entire repository: depending on the product, instructions may load at session start, apply only to matching files, or be discovered later as the agent explores the code.
Why an agent may read files before you ask it to edit
A coding agent needs context that a general-purpose model cannot reliably infer, such as project conventions, architecture notes, or required workflows. Instruction files can provide that context before the agent acts. This is why setup or file activity may appear before the agent answers your first prompt.
There are different ways this happens. A product may load applicable instructions at session start, include a scoped rule when it matches the work, or use search and other tools to discover relevant files during repository exploration. Those timings are not interchangeable, and none by itself means that every source file has been read.
What different coding agents document
The behavior varies by product and configuration. These examples describe the cited products’ documentation, not every coding agent or runtime.
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| Product | Documented behavior | What that does not mean |
|---|---|---|
| Cursor | Supports project rules in .cursor/rules, user rules, AGENTS.md, and the legacy .cursorrules. Applied rule contents enter model context at the start; project rules can be scoped or included based on relevance. Cursor’s rules documentation. |
It does not establish that Cursor reads the whole repository at startup. |
| Cursor CLI | Its documentation says the CLI reads root-level AGENTS.md and CLAUDE.md, if present, and applies them alongside .cursor/rules. Cursor CLI rules documentation. |
This statement is specific to Cursor CLI; it should not be generalized to every Cursor experience. |
| Claude Code | Reads applicable CLAUDE.md files at or above the working directory at session start. Subdirectory files load on demand when Claude reads files there. Anthropic’s CLAUDE.md guide. |
Which files apply depends on directory scope and session context; nested files are not all necessarily loaded at startup. |
| Codex CLI | Enumerates instruction files from ~/.codex and directories from the repository root to the current working directory, merges them in order, and injects the resulting instructions before the user prompt. OpenAI’s AGENTS.md guide. |
This describes Codex CLI, not every OpenAI agent runtime. |
| VS Code agent context | Describes context assembled from instructions, referenced files, and tool outputs. A code search can lead an agent to read files that inform a later model request. VS Code’s agent context documentation. | This is an example of iterative discovery, not proof that all editor agents use the same startup process. |
Project instructions are not the same as reading the repository
Instruction files are a selected source of guidance, not a synonym for the codebase. A root-level instruction may apply broadly, while a rule scoped to a path may matter only for work in that part of the project. Other files may enter context only after an agent searches for or opens them. VS Code’s description of search-led context building illustrates this later, tool-driven path.
Working directory also matters. Claude Code’s documented behavior considers files at or above that directory at session start, while nested instruction files are loaded on demand. Codex CLI describes enumerating instruction files along the path from the repository root to the current working directory. If the agent starts in a different directory, the available instructions may differ.
What early context changes—and what it cannot guarantee
Instructions can make project-specific expectations available to the model before it acts. That can help the agent choose an approach that fits the project rather than relying only on generic conventions. But availability is not proof of perfect compliance: an instruction file guides the model; it does not guarantee that every instruction will be followed in every response.
Keep instructions useful and proportionate. OpenAI’s September 11, 2026 guidance cautions against requiring broad documentation or a full repository map for every small change, noting that such a demand is excessive for a typo fix. Prefer concise guidance relevant to recurring work, and use scoped references when only certain tasks need additional detail. OpenAI’s AGENTS.md guidance.
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How to interpret startup file activity
- Instructions appear before the first answer: the product may load applicable project guidance at session start or inject discovered instructions before the prompt.
- A file is read after the agent searches: that is later exploration, not necessarily startup loading.
- Some directories’ rules appear only for certain work: the product may use path scope or relevance-based inclusion.
- The behavior differs between tools: check documentation for the specific product, version, configuration, and working directory rather than assuming a universal policy.
The cited vendor documentation, as represented on October 4, 2026, establishes different mechanisms for Cursor, Cursor CLI, Claude Code, Codex CLI, and VS Code agent context. It does not establish one startup sequence for all coding agents.
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