For developers

JSON Guarantee API

Cheap models advertise JSON mode — then ship empty bodies, truncated strings, and markdown fences. SureJSON is the drop-in layer that only returns parseable JSON (or an honest failure).

Real pain

Why production parsers keep breaking

Empty JSON mode responses Providers (including DeepSeek) document that response_format: json_object can still return empty content — especially with thinking modes and tight token budgets.
Truncation = invalid JSON Hit max_tokens mid-object and JSON.parse dies. finish_reason: length shows up after the damage.
Valid JSON ≠ usable schema JSON mode only means “parseable,” not “has your keys.” Pipelines fail silently on missing fields and wrong enums.
Markdown and chatter leak through Models wrap JSON in fences or add “sure, here you go” — your catch blocks become the product.

Solution

Two ways to ship sure JSON

Drop-in OpenAI client Point base_url at SureJSON. Keep /v1/chat/completions. Model: surejson-fast. Same SDK, guaranteed parseable content path.
Sure Envelope — POST /v1/sure Skip JSON.parse. Get { ok, guarantee, data }. If anything is empty or unparseable, you get a structured failure — not a broken string.

Quickstart

Swap the base URL. Keep your code.

Claim a free key from the operator workspace, then call the API.

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_SUREJSON_KEY",
    base_url="https://surejson.com/v1",
)

res = client.chat.completions.create(
    model="surejson-fast",
    messages=[
        {"role": "system", "content": "Return ONLY valid JSON."},
        {"role": "user", "content": "Extract name and company from: Sam Ortiz at RiverCo"},
    ],
    response_format={"type": "json_object"},
)

print(res.choices[0].message.content)  # always parseable when ok

Or use the Sure Envelope — no parse dance:

curl -s https://surejson.com/v1/sure \
  -H "Authorization: Bearer YOUR_SUREJSON_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "input": "Extract name and company from: Sam Ortiz at RiverCo",
    "schema_hint": "{\"name\": string, \"company\": string}"
  }'

# → { "ok": true, "guarantee": "parseable_json", "data": { ... } }

Live JSON lab

Prove the guarantee in your browser.

Free. Uses the same key as the everyday workspace.

What should become JSON? Schema hint (optional)

Get free key

Endpoints

What you call

POST /v1/sure: Sure Envelope. Returns { ok, guarantee, data } or structured failure. Best DX when you never want to catch parse errors.
POST /v1/chat/completions: OpenAI-compatible drop-in. Use any OpenAI SDK with base_url=https://surejson.com/v1.
POST /v1/credits/claim: Free start key (also created from the operator workspace).
GET /v1/credits · GET /v1/models: Balance + model list.

← Free everyday workspace (operators)