Last updated: March 25, 2026
Big-3 focus: this guide compares Claude Code, Codex, and Gemini Pro across software delivery tasks. Select a domain below to see which agent is currently best suited for the work.
Best for repo-wide synthesis when plans depend on broad code and docs context.
Stronger when planning output needs tighter, cleaner specification writing.
Handles large-context debugging and cross-system discovery with minimal setup.
Faster for narrower probes where quick iteration matters more than total context size.
Best for fast UI iteration with strong spatial output quality.
Useful when design implementation must follow a large design system or brand corpus.
Most natural UX and marketing voice control for user-facing copy embedded in UI flows.
Best backup when tone must be aligned against very large reference material sets.
Fastest loop for responsive components, state wiring, and interface-level polish.
Useful when frontend tasks lean into strict correctness and backend-adjacent logic.
Most deterministic implementation depth for complex logic and secure backend decisions.
Better fallback when clarity, speed, and iterative feedback are higher priority.
Strongest for rigorous infra authoring across Terraform, Docker, and Kubernetes.
Strong when AWS work depends on ingesting large docs and mapping context accurately.
Best for E2E and user-journey testing where browser behavior matters.
Stronger for backend-heavy unit test rigor and edge-case coverage depth.
Fastest at surgical diff reading and actionable, line-level review feedback.
Better when a large PR needs repo-wide dependency and impact tracing.
Best at deep exploit-path logic, race conditions, and hard failure modes.
Useful for broad security sweeps when scanning large repos and policy docs together.
Gemini wins broad-scope diagnosis, while Claude wins fast iterative fixes near active diffs.
Best fallback when you need deterministic, anti-thrashing repair behavior.
Most capable for system-level docs and runbooks that depend on broad context.
Best for tighter API specs and concise, readable docs within focused scopes.
Use Gemini first when the job starts with reading, synthesizing, and organizing large amounts of product, repo, or reference material before code is written.
Investigations
Gemini reads the widest context window with the least setup friction.
Best when logs, docs, and multiple subsystems need to be inspected together before narrowing the next step.
Planning
Gemini is strongest when scope depends on whole-repo pattern recognition.
Use it to turn messy existing systems into implementation paths, migration plans, and refactor maps.
Documentation
Gemini produces the best system-level docs once it can ingest the full operating context.
Ideal for runbooks, architecture overviews, and internal references that depend on broad system understanding.
Claude Code (`claude-4.6-sonnet`)
Better when the planning task becomes a tighter writing problem: cleaner specs, sharper acceptance criteria, and shorter follow-up loops.
Interface work is where the Big-3 consolidation leans hardest on Claude: design translation, frontend implementation, UX copy, and browser-facing QA all fit its fastest loop.
Designing
Claude is strongest for design translation and UI iteration.
`claude-4.6-sonnet` gets closest to live UI preview workflows through fast spatial reasoning and Artifact-style iteration.
Copywriting
Copywriting belongs with interface work, not planning.
Claude is the cleanest for UX text, landing page copy, and product tone without stiff code-shaped phrasing. Keep Codex away from this layer when tone and empathy matter.
Frontend
Claude stays best for responsive UI and component flow.
It handles React, CSS, state wiring, and visual polish in the same quick loop as the copy and design work.
QA / Testing
Claude wins when testing means real user flows.
Best for Playwright, Cypress, and browser-facing assertions where selectors and async behavior need to match the actual UI.
Gemini Pro (`gemini-3.1-pro`)
Best fallback for huge brand books, design systems, or message libraries that need to be absorbed before rewriting UI or copy.
Codex (`gpt-5.3-codex`)
Useful when frontend tasks turn into strict implementation cleanup or backend-oriented test coverage rather than user-facing polish.
When the work turns into deeper implementation logic, infrastructure correctness, or hard security reasoning, Codex becomes the most reliable default.
Backend
Codex thinks more and writes less.
That makes it the strongest Big-3 choice for custom logic, low-level reasoning, and secure implementation paths.
Infrastructure
Codex still wins raw infra authoring.
It is the cleanest option for Terraform, Docker, Kubernetes, and generally rigorous system configuration.
Security Audit
Security rewards the deepest exploit-path logic.
Codex is the Big-3 leader for race conditions, cryptography misuse, and logic flaws that are easy for lighter models to miss.
Claude Code (`claude-4.6-sonnet`)
Strong fallback for backend tasks that still need faster iteration or explanation-heavy collaboration rather than the strictest implementation discipline.
Gemini Pro (`gemini-3.1-pro`)
Strong for AWS-heavy work when service knowledge and broad documentation context matter more than raw infra syntax alone.
Validation is where Claude’s speed matters again: PR review, UX-aware testing, and fast iteration against active code changes all benefit from the shortest loop.
Code Review
Claude is best for surgical diff reading and line-level feedback.
It is fastest at catching logical edge cases without turning a routine review into a heavy architecture exercise.
QA / Testing
Claude is the strongest default for browser and interaction testing.
Use it when test intent is close to real user behavior instead of pure backend coverage math.
Gemini Pro (`gemini-3.1-pro`)
Better when a large PR needs wider impact analysis across a big codebase rather than only line-by-line review speed.
Codex (`gpt-5.3-codex`)
Strong backup for backend-heavy test suites where strict edge-case coverage matters more than front-end flow realism.
Reliability work is the one stage where a single winner is less honest than the bug shape itself: Claude wins quick review loops, Gemini wins large-scope diagnosis, and Codex is strongest when you need methodical anti-thrashing execution.
Claude lead
Best for fast bug isolation close to an active diff or recently changed code.
Gemini lead
Best for architectural failures spread across logs, docs, and many moving files.
Codex fallback
Best when the first-pass agent is thrashing and you need a stricter, less creative repair loop.