What is Convex Functions?

A guide for writing Convex backend functions, including database queries, data-changing mutations, external-service actions, and HTTP endpoints. Convex is a platform for building backend code alongside an application.

Use it when creating read-only queries, mutations that change data, actions that call external services, or HTTP actions for webhooks and APIs. It covers argument validation and the rules for each function type.

It helps keep these functions’ inputs, errors, database access, and runtime behavior correct. It also points developers to the current Convex documentation before implementation.

How powroom/flins configures Claude Code and Codex

Reuse

Borrowing it

Nothing to install: this file belongs to powroom/flins. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/powroom/flins/main/.agents/skills/Convex Functions/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/powroom/flins

Made for: Claude Code, Codex.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/powroom/flins/convex-functions.svg)](https://agentmods.dev/skills/powroom/flins/convex-functions)

Your own site

<a href="https://agentmods.dev/skills/powroom/flins/convex-functions"><img src="https://agentmods.dev/badge/skills/powroom/flins/convex-functions.svg" alt="Measured on agentmods" height="20"></a>

Per session 28 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 2,744 The whole file, excluding the scripts and references it only reads on demand.

Security scan B 1 finding. A grade says what 26 rules found in the file — not that it is safe.

Origin 94% copy Near-identical to another mod 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.

Model	Per session	Once invoked
Fable 5.1	$0.00028	$0.02744
Opus 5	$0.00014	$0.01372
Sonnet 5	$0.00006	$0.00549
Haiku 4.5	$0.00003	$0.00274

Measured 8d ago against content hash 0aedfc07ddda, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade B, and why

Convex Functions scanned grade B with 1 finding 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 8d 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.

Sends data to an external URLmediumData exfiltration

A POST to an outside endpoint may be telemetry or may be exfiltration; either way the mod talks to somewhere, and you should know where.

const response = await fetch("https://api.email.com/send", { method: "POST",

Origin

This is a copy

94% identical to convex-functions — 65 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.

.agents/skills/Convex Functions/SKILL.md · 442 lines

How it starts

The opening of the file, as written. The whole thing — 442 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Convex Functions

Master Convex functions including queries, mutations, actions, and HTTP endpoints with proper validation, error handling, and runtime considerations.

Documentation Sources

Before implementing, do not assume; fetch the latest documentation:

Primary: https://docs.convex.dev/functions
Query Functions: https://docs.convex.dev/functions/query-functions
Mutation Functions: https://docs.convex.dev/functions/mutation-functions
Actions: https://docs.convex.dev/functions/actions
HTTP Actions: https://docs.convex.dev/functions/http-actions
For broader context: https://docs.convex.dev/llms.txt

Instructions

Function Types Overview

Type	Database Access	External APIs	Caching	Use Case
Query	Read-only	No	Yes, reactive	Fetching data
Mutation	Read/Write	No	No	Modifying data
Action	Via runQuery/runMutation	Yes	No	External integrations
HTTP Action	Via runQuery/runMutation	Yes	No	Webhooks, APIs

Queries

Queries are reactive, cached, and read-only:

import { query } from "./_generated/server";
import { v } from "convex/values";

export const getUser = query({
  args: { userId: v.id("users") },
  returns: v.union(
    v.object({
      _id: v.id("users"),
      _creationTime: v.number(),
      name: v.string(),
      email: v.string(),
    }),
    v.null()
  ),
  handler: async (ctx, args) => {
    return await ctx.db.get(args.userId);
  },
});

// Query with index
export const listUserTasks = query({
  args: { userId: v.id("users") },
  returns: v.array(v.object({
    _id: v.id("tasks"),
    _creationTime: v.number(),
    title: v.string(),
    completed: v.boolean(),
  })),
  handler: async (ctx, args) => {
    return await ctx.db
      .query("tasks")
      .withIndex("by_user", (q) => q.eq("userId", args.userId))
      .order("desc")
      .collect();
  },
});

Mutations

Mutations modify the database and are transactional:

Read the full file on GitHub · 442 lines

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.

8d ago First seen · 442 lines · 28 tokens per session scan B 0aedfc07ddda

Subscribe to this mod's changes

Convex Functions is a skill published in the GitHub repository powroom/flins (39 stars, last pushed 5mo ago), licensed MIT. It adds 28 tokens to every session and 2,744 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it B with 1 finding (sends data to an external url). It is 94% identical to convex-functions, differing in 65 lines, and is treated as a copy.

Backend and APIs Databases actions agent agentic-ai ai ai-agents ai-tools convex functions http mutations queries

flins: Skill for Claude Code