Advanced Best Practices - Common Mistakes

Developers who adopt Claude Code make recurring mistakes that reduce their productivity by 30 to 60%. This guide documents the 10 most common pitfalls in professional workflows, debugging, and teamwork, with concrete corrections and before/after examples for each case.

Common mistakes related to advanced best practices of Claude Code represent the main obstacles encountered by developers in professional environments. Claude Code adoption in companies exceeds 40% among French-speaking development teams, according to Anthropic. Yet, 7 out of 10 developers reproduce the same anti-patterns in their daily workflows.

How to avoid critical workflow mistakes with Claude Code?

Before detailing each mistake, here is a ranking by severity and frequency. This table allows you to quickly identify the problems to fix as a priority in your advanced best practices.

Key takeaway: Prioritize critical mistakes - they account for 80% of productivity losses.

What are the problems caused by poorly structured context? (Mistake 1)

Severity: Critical - Sending disorganized context to Claude Code is the most widespread and costly mistake.

Context is the fuel of Claude Code. Poorly structured context produces generic, off-topic, or incomplete responses. a prompt with structured context generates responses 3 times more accurate than a raw prompt.

Concretely, the problem occurs when you send a code block without explaining the architecture, constraints, or objective. Claude Code does not guess your intent - it infers from what you provide.

# Incorrect - context absent
$ claude "fix this bug"

# Correct - structured context
$ claude "In the file src/auth/login.ts, the validateToken function
  returns undefined when the JWT expires instead of throwing a TokenExpiredError.
  Stack: Node.js 22, Express 5, jsonwebtoken 9.0.2"

To dive deeper into context management, check the guide on common context management mistakes which covers the most frequent cases.

In practice, structured context includes: the file concerned, the expected behavior, the observed behavior, and the tech stack. These 4 elements reduce back-and-forth by 70%.

Key takeaway: Systematically structure your context into 4 elements - file, expected, observed, tech stack.

How to fix the absence of a CLAUDE.md file? (Mistake 2)

Severity: Critical - Not configuring a CLAUDE.md file is equivalent to using Claude Code without project memory.

CLAUDE.md is the persistent memory file of Claude Code. It stores conventions, critical paths, and preferences for your project. Without it, each new session starts from scratch.

projects configured with a complete CLAUDE.md reduce setup time by 45% per session. In practice, 70% of professional projects do not have one during initial adoption.

# Incorrect - no CLAUDE.md
# The developer repeats the same instructions every session

# Correct - CLAUDE.md at the project root
# CLAUDE.md
## Architecture
- Framework: Next.js 15 (App Router)
- Database: PostgreSQL 16
- ORM: Prisma 5.22
- Tests: Vitest + Testing Library

## Conventions
- Naming: camelCase for variables, PascalCase for components
- Commits: Conventional Commits format
- Comment language: English

Verify that your CLAUDE.md covers at minimum: architecture, naming conventions, and build/test commands. Find specific pitfalls in the CLAUDE.md memory system errors guide.

SFEIR Institute teams observe that adding a CLAUDE.md reduces style divergence by 60% among team members.

Key takeaway: Create a CLAUDE.md from day one - it is the project memory of Claude Code.

Why does debugging without a structured plan waste time? (Mistake 3)

Severity: Warning - Starting a debugging session without a hypothesis or plan consumes on average 3 times more tokens.

Effective debugging with Claude Code follows a precise method. The classic mistake is sending a raw stack trace asking "fix this." Here is the difference between the two approaches.

# Incorrect - raw stack trace without context
$ claude "Error: Cannot read properties of undefined (reading 'map')
  at UserList.tsx:42"

# Correct - hypothesis + context + plan
$ claude "Bug in UserList.tsx:42 - users.map() fails.
  Hypothesis: the users state is not initialized as an empty array.
  Check the initial useState and the return of the /api/users API.
  If confirmed, add a fallback users ?? [] before the .map()"

To master advanced debugging, explore the Claude Code debugging guide which details the complete methodology. In practice, formulating a hypothesis before launching Claude Code divides resolution time by 3.

Key takeaway: Always formulate a hypothesis before debugging - Claude Code validates or invalidates, it does not guess.

How to avoid monolithic prompts? (Mistake 4)

Severity: Critical - A prompt over 500 words sent in a single block produces inconsistent results in 60% of cases.

Monolithic prompts overload the model with too many simultaneous instructions. Claude Code v2.1 processes instructions sequentially - a prompt broken into 3 steps produces a 50% more reliable result.

# Incorrect - monolithic prompt
$ claude "Refactor the auth module, add unit tests,
  migrate to the new API, update the documentation,
  check the permissions and fix the TypeScript types"

# Correct - sequential targeted prompts
$ claude "Step 1: Analyze the src/auth/ module and list the functions
  that use the old v1 API"
# -> Result: 4 functions identified

$ claude "Step 2: Refactor validateToken() to use the v2 API.
  Keep the same return signature"
# -> Result: targeted refactoring

Here is a comparison table of splitting strategies.

Concretely, split each complex task into sub-tasks of 100 words maximum. The advanced Claude Code tips detail other splitting techniques.

Key takeaway: Split your prompts into 100-word steps - accuracy increases by 50%.

Why does ignoring permissions cause production incidents? (Mistake 5)

Severity: Critical - Granting overly broad permissions to Claude Code exposes your environment to uncontrolled modifications.

Claude Code executes system commands. Without safeguards, a poorly formulated instruction can delete files, overwrite Git branches, or modify sensitive configurations. In 2026, 55% of teams have not configured permission restrictions.

// Incorrect - no restriction in settings.json
{
  "permissions": {
    "allow": ["*"]
  }
}

// Correct - granular permissions
{
  "permissions": {
    "allow": ["read", "edit"],
    "deny": ["bash:rm -rf", "bash:git push --force", "bash:drop"],
    "askUser": ["bash:git push", "bash:npm publish"]
  }
}

Configure permissions from installation by following the permissions and security errors guide. In practice, a granular permissions policy prevents 95% of accidental incidents.

The askUser mode is the recommended strategy for high-impact commands. It adds 5 seconds of human validation but prevents accidental deletions.

Key takeaway: Restrict permissions by default and enable askUser for any destructive command.

How to properly integrate Claude Code into a legacy project? (Mistake 6)

Severity: Warning - Launching Claude Code on a legacy project without an onboarding phase produces suggestions incompatible with existing code in 45% of cases.

A legacy project has implicit conventions, obsolete dependencies, and specific patterns. Run a structured onboarding phase before any modification.

# Incorrect - direct modification without onboarding
$ claude "add a search feature to this project"

# Correct - 3-step onboarding
$ claude "Analyze the project structure: list the main folders,
  the framework, the Node.js version, and the component patterns used"

$ claude "Identify the conventions of this project: file naming,
  import style, error handling, state management patterns"

$ claude "Following the identified conventions, add a search feature
  in the existing SearchBar component"

Here is how a structured onboarding impacts quality.

To avoid other startup mistakes, check the common mistakes for first conversations. The SFEIR Institute team recommends spending 5 minutes on onboarding - this investment reduces code review rejections by 40%.

Key takeaway: Invest 5 minutes of onboarding on each legacy project - you will save 30.

What convention conflicts emerge in teams? (Mistake 7)

Severity: Minor - Without a shared CLAUDE.md, each developer configures Claude Code differently, creating style inconsistencies in 40% of pull requests.

Working as a team with Claude Code requires configuration alignment. The problem occurs when 3 developers use 3 different prompt styles on the same project.

# Incorrect - each dev has their own config
# Dev A: "use arrow functions"
# Dev B: "use function declarations"
# Dev C: no preference

# Correct - shared and versioned CLAUDE.md
## Team Conventions (CLAUDE.md at the root)
- Functions: arrow functions for components,
  function declarations for utilities
- Imports: named exports only (no default export)
- Tests: one .test.ts file per module, describe/it in English
- PR: description generated by Claude Code with /pr-description

Version your CLAUDE.md in Git and add it to your onboarding checklist. Check the Git integration errors to avoid merge conflicts on this file.

In practice, a shared CLAUDE.md aligns 90% of conventions within the first week. Teams of more than 4 developers see a 25% reduction in code review comments.

Key takeaway: Version the CLAUDE.md in Git - it is part of the team's source code.

How to leverage slash commands to save time? (Mistake 8)

Severity: Minor - Ignoring built-in slash commands wastes an average of 15% of time per work session.

Claude Code integrates native shortcuts. Claude Code v2.1 offers more than 12 slash commands. Yet, 35% of users never use them.

# Incorrect - doing everything manually
$ claude "analyze this project and create a configuration file"
$ claude "check if there are errors in my setup"

# Correct - using slash commands
$ claude /init      # generates CLAUDE.md automatically
$ claude /doctor    # diagnoses the setup in 30 seconds
$ claude /review    # launches a complete code review

Find the complete list in the slash command errors guide. Memorize at minimum /init, /doctor, and /compact - these 3 commands cover 80% of daily needs.

Key takeaway: Learn 3 essential slash commands - /init, /doctor, and /compact cover 80% of cases.

Why should you systematize the review of AI-generated code? (Mistake 9)

Severity: Warning - Accepting generated code without review introduces bugs in 1 out of 4 PRs, according to a GitClear study (2025).

Claude Code produces functional code in 85% of cases. The remaining 15% contain subtle errors: poor error handling, ignored edge cases, unnecessary dependencies. Systematically check with a checklist.

# Incorrect - accept directly
$ claude "add form validation"
# -> copy-paste the result without review

# Correct - systematic review
$ claude "add form validation"
# -> read the generated code
$ claude /review   # run the automated review
# -> manually check edge cases
$ npm test         # run existing tests

Concretely, spend 2 minutes of review for every 10 minutes of generation. This 1:5 ratio reduces regressions by 70%. The advanced troubleshooting guide covers cases where review reveals recurring anomalies.

The Claude Code training from SFEIR Institute, lasting one day, trains you to set up these review workflows with hands-on labs on real projects. To go further, the AI-Augmented Developer training over 2 days covers complete integration into your CI/CD pipeline.

Key takeaway: Systematically review generated code - 2 minutes of review for 10 minutes of generation.

How to set up an effective feedback loop? (Mistake 10)

Severity: Warning - Not iterating on Claude Code results leaves 35% of improvement potential unexploited.

The feedback loop is the mechanism that improves response quality over time. Without it, you get "good" results but never "excellent" ones.

# Incorrect - one-shot without feedback
$ claude "generate a table component"
# -> use as-is, move to the next task

# Correct - iterative loop
$ claude "generate a table component to display users"
# -> examine the result
$ claude "the table is missing column sorting and pagination.
  Add them using the same pattern as src/components/DataGrid.tsx"
# -> examine and validate
$ claude "add unit tests for sorting and pagination"

Iterate in 2-3 cycles maximum. Beyond 3 cycles, the context degrades. Use /compact to reset context between long cycles, as explained in the best practices tips.

In practice, 3 feedback cycles increase code quality by 40% compared to a single prompt. If you want to master these iterative workflows at an advanced level, the AI-Augmented Developer - Advanced one-day training at SFEIR covers fine-tuning these loops on complex projects.

Key takeaway: Iterate in 3 cycles maximum - beyond that, compact the context with /compact.

What anti-patterns should be eliminated for the Track A final assessment?

To validate Track A, you must demonstrate the absence of these anti-patterns in your daily workflow. Here is the evaluation grid used by trainers.

Evaluate your practice on each criterion before submitting your final assessment. A score of 70% or more on this grid corresponds to the "confirmed practitioner" level. To find all the best practices, check the advanced best practices page.

According to the experience of SFEIR cohorts (2025-2026), developers who correct these 10 mistakes achieve an average score of 85% in the final assessment, versus 52% for those who retain the anti-patterns.

Key takeaway: Fix the 10 mistakes in this guide to aim for 85% on the Track A assessment.