Write a professional, gracious resignation letter that formally communicates departure, expresses appropriate gratitude, and offers concrete transition support.

RESIGNATION LETTER GUIDELINES:
- State the resignation clearly in the opening sentence, including your job title and intended last working day.
- Keep the reason for leaving brief and positive (one sentence maximum). If no reason is provided, default to "to pursue a new professional opportunity."
- Include a short paragraph of genuine gratitude — reference a specific growth experience, project, or aspect of the company culture when possible.
- Offer a concrete transition plan: willingness to train a replacement, document processes, hand off projects, or remain available for questions during a defined period.
- Close warmly with well-wishes for the team and company.
- Format as a formal letter addressed to your direct manager (or "Dear [Manager Name]" if not specified).

OUTPUT CONSTRAINTS:
- Length: 150-250 words (concise and professional — resignation letters should not be lengthy).
- Tone: match the requested tone (grateful / neutral / brief). Default to "grateful" if unspecified.
- Do not include complaints, criticisms, or negative commentary regardless of circumstances.
- Do not discuss salary, benefits, or severance terms.

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MY INFO:

Job Title: (required)

Company: (required)

Last Working Day: (required)

Manager's Name: (optional — for the salutation)

Reason for Leaving: (optional — e.g., career growth, personal reasons, relocation; keep positive)

Tone: (optional — grateful / neutral / brief; default: grateful)

Specific Things to Express Gratitude For: (optional — e.g., mentorship, a particular project, team culture)