IDE Agents vs Terminal CLI Agents: An Honest Decision Guide

IDE agents and terminal/CLI agents are two surfaces for the same model loop, usually shipped by the same vendor. This guide gives you the exact commands, flags, file paths, and cost models for each surface, and a procedure to route any task to the one that fits. The deciding variable is loop length: short, attended, review-heavy work → IDE; long, well-specified, parallel, or unattended → CLI/cloud.

IDE-only affordances

Three capabilities depend on a human watching a cursor; a headless process cannot replicate them.

Inline diffs / hunk-level review — the agent proposes edits as diffs in the file; you accept or reject per hunk before anything lands. Cursor's Agent snapshots edits as Checkpoints so you can roll back without touching Git history.

Tab completion — Cursor Tab suggests code from your recent edits, surrounding code, and linter errors; it predicts multi-line edits, cross-file edits, and jump-in-file (press Tab again to navigate to the next likely edit). Tab is unlimited on all paid Cursor plans. GitHub Copilot code completions and next-edit suggestions are not billed and stay unlimited on paid plans — a different cost basis from agent/chat usage.

Prebuilt semantic index — Cursor splits files into chunks, embeds them as vector embeddings, and stores the embeddings remotely. Semantic search becomes available at ~80% completion and the index auto-syncs every ~5 minutes. Exclusions honor .gitignore and .cursorignore.

CLI / cloud-only affordances

These three capabilities require no human at the cursor: autonomy, parallelism, and unattended execution.

Headless, non-interactive runs are the CLI's signature. Claude Code runs with -p / --print; --output-format accepts text (default), json (includes total_cost_usd + session ID), and stream-json (newline-delimited events). --json-schema enforces structured output (returned in structured_output). --bare skips auto-discovery of hooks, skills, plugins, MCP, memory, and CLAUDE.md — "the recommended mode for scripted and SDK calls." Piped stdin is capped at 10MB (as of v2.1.128). OpenAI Codex CLI mirrors this with codex exec: progress streams to stderr, the final message to stdout; it must run inside a Git repo (override --skip-git-repo-check); --json emits a JSON-Lines event stream; --output-schema <path> enforces a JSON Schema; --sandbox sets the permission level; codex exec resume --last continues a prior run.

Cloud / async PR agents detach work from your machine. GitHub's Copilot coding agent runs in an ephemeral environment powered by GitHub Actions, edits on a branch, runs tests, and opens a PR — capped at a 59-minute execution limit per task. Cursor's Cloud Agents run in sandboxed cloud VMs from an ephemeral checkout. Devin (Cognition, the new identity of Windsurf) is an autonomous cloud agent fused with a desktop editor.

Instruction / "rules" files by surface

Each surface reads configuration from different paths. AGENTS.md is the cross-vendor convergence point — Cursor, Copilot, and others all read it.

Cost models

Two cost classes: completions are cheap-to-free; agent loops are metered per token. A Tab completion or next-edit suggestion costs $0 on a paid plan; an agent loop that re-reads context every turn is billed per input, output, and cached token. The three subscription shapes below differ structurally — the shape determines which surface is cheap for a given workload.