What is the difference between a job description and a person specification?

The job description describes the role; the person specification describes the person who could do it. They answer different questions, and reading them as one document is why applications miss the mark.

The job description covers:

Purpose — why the role exists.

Key responsibilities — what the postholder actually does, usually as a list of duties.

Reporting lines — who they report to and who reports to them.

Scope — budget, team size, geography.

Terms — grade, hours, location, contract type.

The person specification covers the criteria you will be assessed against, usually split:

Essential — you must evidence every one of these. Missing an essential criterion is frequently an automatic rejection at shortlisting, particularly in the public sector where scoring is formalised.

Desirable — differentiators between candidates who all meet the essentials. You do not need all of them.

Criteria are typically grouped into qualifications, experience, knowledge, skills and attributes, and each usually notes how it will be assessed — application form, interview, test, presentation.

How to actually use them:

Write your application against the person specification, not the job description. This is the single most consequential point. Shortlisters score you criterion by criterion, and a beautifully written application that does not map onto the criteria will score poorly.

Address every essential criterion explicitly, in the order listed, using the same language. Do not make the reader infer that your experience counts.

Use the job description to understand the role and to pitch your examples at the right level and context.

Note the assessment method column. If a criterion says "assessed at interview", you need not exhaust it in the form — but if it says "application", it must be there.

In the public sector especially, shortlisting against the specification is frequently mechanical, so "it's obvious from my CV" is not a strategy.