Conciseness

Largely efficient and dense with Claude-relevant operational detail (the 10-DNS-lookup limit, 'pct=100; adkim=s', bounce targets, warm-up schedules), but includes some explanation of concepts Claude already knows, e.g. 'A cryptographic signature on each outgoing email', 'DKIM proves the message wasn't modified in transit', and 'Mailbox providers (Gmail, Outlook, Yahoo) score every sender'. Not level 5 due to these trimmable passages; not level 3 because the padding is minor and most tokens earn their place.

Actionability

Fully executable guidance for the common cases: copy-paste SPF/DKIM/DMARC record examples, runnable audit commands ('dig +short txt example.com'), specific thresholds ('target: under 2%', 'under 0.1%', 'pct=10'), named tools (mxtoolbox.com, Google Postmaster Tools), and ordered fix procedures per protocol. Not level 4: there are no material gaps; examples cover the common audit and remediation cases.

Workflow Clarity

The 8-step workflow is clearly sequenced with explicit validation checkpoints and feedback loops: 'Verify lookup count is under 10', 'Verify with a test send (check headers for dkim=pass)', 'Watch reports for at least 2-4 weeks' before advancing, and a gradual pct=10 ramp before p=reject, plus a dedicated 'Failure patterns' section for error recovery. Not level 4: checkpoints and recovery guidance are explicit at each risky stage, including the inherently destructive p=reject transition.

Progressive Disclosure

Good structure: the DMARC rollout depth is correctly split into the one-level-deep 'references/dmarc-rollout-playbook.md' (a real file whose content matches its description), signaled in a dedicated 'Reference files' section with a clear summary. Not level 5: the ~280-line body inlines substantial pillar/workflow detail while only the DMARC topic is split out, and the playbook reference is not surfaced at its point of use in Step 2's DMARC fix order; not level 3 because the reference is clearly signaled and navigation is easy.

Specificity

Lists multiple specific concrete actions — 'setting up email authentication (SPF, DKIM, DMARC), diagnosing emails landing in spam, planning a domain reputation strategy, monitoring sender reputation, or hardening against email spoofing' — covering the deliverability domain comprehensively. Not level 4: coverage has no minor gaps; every listed action is concrete rather than generic.

Completeness

Explicitly answers both what ('Make sure email actually reaches inboxes' with the enumerated capabilities) and when ('Use this skill when...' plus 'Triggers on...'). Not level 4: the 'when' is not merely present but given twice with concrete trigger phrases, matching the level-5 example structure.

Trigger Term Quality

Comprehensive natural trigger terms with synonyms and both technical and colloquial phrasings: 'email deliverability, SPF, DKIM, DMARC, spam folder, sender reputation, mailbox provider, soft bounces, bounce rate, BIMI, MTA-STS, deliverability audit' plus the natural-language case 'when a marketing or transactional email isn't reaching users'. Not level 4: it goes beyond good coverage by including common variations users actually say (e.g., 'spam folder', 'soft bounces').

Distinctiveness Conflict Risk

Mostly distinct — triggers like SPF, DKIM, DMARC, spam folder, and bounce rate are unambiguously deliverability-specific. Not level 5: 'planning a domain reputation strategy' and 'marketing... email isn't reaching users' carry minor overlap risk with closely related domain-strategy or email-marketing skills, matching the level-4 anchor; not level 3 since the niche and triggers remain clearly distinguishable.