Error: invalid wrangler.toml" duplicate top-level key

TL;DR

TOML forbids defining the same key twice, and wrangler rejects the whole file when it finds one. The usual culprit is a copy-pasted section like a second [vars] block or two [env.staging] tables. Find the repeated key, merge the two blocks into one, and validate the file parses before deploying.

Error: invalid wrangler.toml: duplicate top-level key "vars"

Steps

1. List every top-level key and section header in the file and look for repeats:

grep -n '^\[' wrangler.toml
grep -n '^[a-z_]* =' wrangler.toml

Expected: each section header and each top-level key appears exactly once. Any line number pair showing the same name twice is the offender.

1. Open the file around those line numbers and merge the duplicates into a single block. Keep all the settings, just under one header.

Expected: one [vars] block, one compatibility_date line, one table per environment name.

1. Validate the file parses as TOML:

python3 -c "import tomllib; tomllib.load(open('wrangler.toml','rb')); print('valid')"

Expected: the script prints "valid". If it errors, read the message; it names the offending key and line.

1. Deploy:

wrangler deploy

Expected: config validation passes and the deploy proceeds.

Use this when

• Wrangler reports "invalid wrangler.toml" with a duplicate key
• The error appeared right after hand-editing or merging the config
• Two environment blocks share a name after a copy-paste

Not for this skill when

• The config is wrangler.jsonc; the duplicate idea is the same but the syntax and validator differ
• The error is about an unknown or misspelled key rather than a duplicate
• The deploy fails on bindings or auth, not on config parsing

Variant phrasings

• wrangler.toml duplicate key error
• invalid wrangler.toml duplicate top-level key vars
• wrangler config duplicate table header

Why it happens

TOML is strict: a key or table defined twice is a parse error, not a merge. It happens most often when environment sections are duplicated during copy-paste, when two people edit the file in a merge, or when a [vars] block gets added at the bottom while one already exists near the top.

Edge cases

• Wrangler does not support config inheritance or includes; do not try to work around the duplicate by splitting the file.
• A duplicate inside an [env.name] table (two vars under the same env) fails the same way; check env-scoped sections too.
• Comments and blank lines never cause this; only real keys and headers count.
• If the file is generated by a script, fix the generator or the duplicate comes back on the next run.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstdMxxd1Vy7GhSKa42H4FWw