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.
npx skills add ccarvalho-eng/codex-elixir-phoenix --skill elixir-phoenix-ecto-constraint-debuggit clone --depth 1 https://github.com/ccarvalho-eng/codex-elixir-phoenixWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/ccarvalho-eng/codex-elixir-phoenix/elixir-phoenix-ecto-constraint-debug)<a href="https://agentmods.dev/skills/ccarvalho-eng/codex-elixir-phoenix/elixir-phoenix-ecto-constraint-debug"><img src="https://agentmods.dev/badge/skills/ccarvalho-eng/codex-elixir-phoenix/elixir-phoenix-ecto-constraint-debug/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/ccarvalho-eng/codex-elixir-phoenix/elixir-phoenix-ecto-constraint-debug"><img src="https://agentmods.dev/badge/skills/ccarvalho-eng/codex-elixir-phoenix/elixir-phoenix-ecto-constraint-debug.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00025 | $0.00680 |
| Opus 5.5 | $0.00010 | $0.00272 |
| Sonnet 5.5 | $0.00005 | $0.00136 |
| Haiku 4.5 | $0.00003 | $0.00068 |
Grade A, and why
elixir-phoenix-ecto-constraint-debug 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 1mo 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.
This is a copy
86% identical to ecto-constraint-debug — 19 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 70 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Ecto Constraint Debugging
Systematic approach to diagnosing constraint violations. Load when you see Ecto.ConstraintError, unique_constraint, foreign_key_constraint, or constraint-related changeset errors.
Iron Laws
- READ THE CONSTRAINT NAME — The constraint name (e.g.,
links_url_index) tells you exactly which index/constraint failed. Parse it from the error message first - CHECK MIGRATION BEFORE CODE — Verify the constraint definition in
priv/repo/migrations/matches what the schema expects - TRACE ALL INSERT PATHS — Find every code path that inserts into the constrained table. The bug is often in a path you didn't consider
- RACE CONDITION UNTIL PROVEN OTHERWISE — If validation passes but constraint fails, assume concurrent inserts until you prove a single-request cause
Step-by-Step Debugging
Step 1: Parse the Error
Extract from the error message:
- Constraint name (e.g.,
users_email_index) - Table name (e.g.,
users) - Operation (insert, update, or delete)
- Conflicting values (if available in logs)
Step 2: Find the Migration
Use rg to search for the constraint name in priv/repo/migrations/. Also check for create unique_index, create index, add constraint.
Verify: Does the migration constraint match the schema's unique_constraint/3 or foreign_key_constraint/3 call?
Step 3: Find the Schema
Use rg to find constraint handling in changesets (unique_constraint, foreign_key_constraint, check_constraint) in lib/.
Step 4: Trace Insert Paths
Find ALL callers that insert/update this schema:
Use rg to find all insert/update paths (Repo.insert, Repo.update, Repo.insert_all, cast_assoc) in lib/.
Step 5: Identify the Cause
| Symptom | Likely Cause | Fix Pattern |
|---|---|---|
| Same user triggers twice | Race condition (double-click, retry) | Upsert with on_conflict |
| Multiple parents share child | cast_assoc doesn't dedup across changesets |
Dedup before building changesets |
| Concurrent API requests | Missing transaction isolation | Wrap in Repo.transaction or use upsert |
| Migration added constraint to existing data | Data violates new constraint | Backfill or clean data first |
What ships with it
2 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 1mo ago First seen · 70 lines · 25 tokens per session scan A 2fec8befb9c3
elixir-phoenix-ecto-constraint-debug is a skill published in the GitHub repository ccarvalho-eng/codex-elixir-phoenix (11 stars, last pushed 5mo ago), licensed MIT. It adds 25 tokens to every session and 680 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 86% identical to ecto-constraint-debug, differing in 19 lines, and is treated as a copy.
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