Convex Migrations

What it does

When your agent uses it

• Removing a field
• Changing a type
• Splitting a table
• Deploy fails with a schema validation error on existing documents

Example prompts

• “Use the convex-migrations skill to change a live Convex schema without downtime: make a field optional, backfill in batches, flip the validator…”
• “/convex-migrations”

Requirements

• Node.js

Workflow steps

6 steps, taken from the first numbered list in SKILL.md.

1. 1Make the field optional in convex/schema.ts (or add the new field as v.optional).
2. 2Deploy with npx convex dev. Update readers to handle undefined and writers to set the new shape.
3. 3Backfill existing documents in batches with an internal mutation or the migrations component.
4. 4Flip the validator to its final shape (v.string() instead of v.optional(v.string()), or drop the old field).
5. 5Deploy again. Validation now passes because every document already matches.
6. 6Clean up: delete fallback code, remove the backfill function, drop stale indexes.

What it can do on your machine

Read from SKILL.md and the folder at commit 82d1ce2. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • npx

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Hosts in commands or code, which the agent is likely to contact:

  • api.dicebear.com

  Also links to:

  • docs.convex.dev
  • convex.dev
  • stack.convex.dev

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Convex Migrations loads about 2.1k tokens when it runs, and up to ~5.5k if it reads all its reference files. Until then it costs about 88 tokens; SKILL.md has 857 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~88

When it runs · the whole SKILL.md, loaded when a task matches

~2.1k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~5.5k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from waynesutton/builder-skills at commit 82d1ce2, republished under its Apache-2.0 licence (© waynesutton). 857 words, ~2,149 tokens.

name

convex-migrations

description

Changes a live Convex schema without downtime: make a field optional, backfill in batches, flip the validator, then clean up. Uses the @convex-dev/migrations component where it fits. Use when renaming or removing a field, changing a type, splitting a table, or when deploy fails with a schema validation error on existing documents.

// convex/migrations.ts
import { internalMutation } from "./_generated/server";
import { internal } from "./_generated/api";
import { v } from "convex/values";

const BATCH_SIZE = 100;

export const backfillAvatarUrl = internalMutation({
  args: { cursor: v.union(v.string(), v.null()) },
  returns: v.null(),
  handler: async (ctx, args) => {
    const result = await ctx.db
      .query("users")
      .paginate({ numItems: BATCH_SIZE, cursor: args.cursor });

    for (const user of result.page) {
      // Idempotent: skip documents that already have the field
      if (user.avatarUrl === undefined) {
        await ctx.db.patch(user._id, {
          avatarUrl: defaultAvatar(user.name),
        });
      }
    }

    // Reschedule with the cursor until the table is exhausted
    if (!result.isDone) {
      await ctx.scheduler.runAfter(0, internal.migrations.backfillAvatarUrl, {
        cursor: result.continueCursor,
      });
    }
    return null;
  },
});

function defaultAvatar(name: string): string {
  return `https://api.dicebear.com/7.x/initials/svg?seed=${encodeURIComponent(name)}`;
}

npx convex run migrations:backfillAvatarUrl '{"cursor": null}'

// convex/convex.config.ts
import { defineApp } from "convex/server";
import migrations from "@convex-dev/migrations/convex.config.js";

const app = defineApp();
app.use(migrations);
export default app;

// convex/migrations.ts
import { Migrations } from "@convex-dev/migrations";
import { components } from "./_generated/api";
import { DataModel } from "./_generated/dataModel";

export const migrations = new Migrations<DataModel>(components.migrations);

export const addDefaultRole = migrations.define({
  table: "users",
  migrateOne: async (ctx, user) => {
    if (user.role === undefined) {
      await ctx.db.patch(user._id, { role: "user" });
    }
  },
});

npx convex run migrations:addDefaultRole '{"dryRun": true}'
npx convex run migrations:addDefaultRole

Schema validation failed
Document with ID "j57abc..." in table "users" does not match the schema:
Object is missing the required field `avatarUrl`.
Consider wrapping the field validator in `v.optional(...)` if this is expected.

© waynesutton, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 5 other files (references, assets) in skills/convex-migrations of waynesutton/builder-skills.

• SKILL.md
• agents/openai.yaml
• assets/large-logo.png
• assets/small-logo.svg
• references/migration-patterns.md
• references/migrations-component.md

Open the folder on GitHubat commit 82d1ce2