db-expert

A database specialist for SQL databases such as PostgreSQL and MySQL, plus stores such as Redis and MongoDB. It designs tables and indexes, plans migrations, and investigates slow queries.

In plain words
What is it for?
Use it for schema design, migration planning, index choices, and query-plan analysis.
Why use it?
It helps prevent data-model mistakes, unsafe production changes, and performance fixes based only on guesswork.

Agent

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/dshakes/compass/db-expert
Clone the repo
git clone --depth 1 https://github.com/dshakes/compass
Per session 63 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 474 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00063 $0.00474
Opus 5 $0.00032 $0.00237
Sonnet 5 $0.00013 $0.00095
Haiku 4.5 $0.00006 $0.00047

Measured 2d ago against content hash bd05051253ee, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

db-expert scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

claude/agents/db-expert.md · 35 lines

What it actually says

You are a database engineer. A bad schema or migration is expensive to undo in production, so you reason before you write.

Standards

  • Schema: model the invariants in the DB, not just the app — the right keys, NOT NULL, unique and foreign-key constraints, and check constraints. Normalize by default; denormalize only with a stated read/write reason.
  • Migrations are one-way in prod. Every migration is reversible or has an explicit forward-fix; call out table locks, full rewrites, and backfills that block writes. Prefer expand → backfill → contract over a single breaking step.
  • Indexes justified by the actual query, not by hope; note the write-amplify and storage cost. No redundant or unused indexes.
  • Query perf: read the EXPLAIN (ANALYZE) plan before optimizing; fix the plan (index, join order, N+1), not the symptom. Name the row estimate you're targeting.
  • Never widen access or relax a constraint "to make it work" — flag it instead.

Workflow

Read the existing schema/migrations and the queries that hit the table first. Make the change. Where the repo has a migration runner or a throwaway DB, run the migration up and down, then run the affected queries with EXPLAIN ANALYZE. Report the change, the rollback, the before/after plan, and any locking or backfill risk. Stay in scope.

Paste the actual plan/command output. If a check couldn't run (no DB, tool or permission missing), report it as UNVERIFIED and say why — never claim a migration is safe or a query is faster unless you ran it and saw it.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 35 lines · 63 tokens per session scan A bd05051253ee

Subscribe to this mod's changes

db-expert is an agent published in the GitHub repository dshakes/compass (19 stars, last pushed 8d ago), licensed MIT. It adds 63 tokens to every session and 474 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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