Monitoring the CometAPI chat completions contract

Last reviewed: 2026-05-10

Who this is for: platform engineers, SREs, and application owners who call CometAPI’s chat completions endpoint from production systems and need contract-level monitoring, not just uptime checks.

For related reliability material, see the LLM API reliability home and the posts index. Editorial assumptions for this satellite are documented at editorial notes.

Key takeaways

• Treat the chat completions API as a contract with observable signals: request shape, auth behavior, response schema, token usage fields, latency, finish reasons, and error classes.
• Monitor both transport success and semantic contract health. A 200 response is not enough if choices, message.content, or usage fields disappear or change shape.
• Keep validation probes small, deterministic, and explicitly marked as synthetic traffic.
• Verify endpoint path, auth header format, required request fields, response fields, error behavior, streaming behavior, and any billing or rate-limit assumptions against the CometAPI API documentation before enforcing alerts.
• Use thresholds below as starting points only. Tune them against your own baseline, traffic mix, timeout policy, and business impact.

Concise definition

A chat completions reliability contract is the set of assumptions your application makes when calling a chat completions API: where to send the request, how to authenticate, which request fields are accepted, which response fields are returned, how failures are represented, and what operational signals can be monitored to detect drift.

For CometAPI, the primary public source checked for this draft is the CometAPI API documentation page for the chat completions endpoint: https://apidoc.cometapi.com/api-13851472.

Contract details to verify

Use this table before you turn any signal into a paging alert. The goal is to separate “documented contract” from “assumption copied from an SDK, example, or prior provider.”

Monitoring signals that catch contract drift

1. Request contract signal

Emit a compact schema fingerprint for every outbound call. Do not log prompt text unless your data policy explicitly permits it.

Recommended fields:

• endpoint route, not full URL with query strings
• HTTP method
• model identifier requested
• message count
• whether system, user, assistant, and tool messages are present
• whether streaming is requested
• timeout budget
• client library or gateway version
• redacted tenant or workload identifier

Example metrics:

• llm_request_total{provider="cometapi",endpoint="chat_completions"}
• llm_request_schema_invalid_total
• llm_request_stream_enabled_total
• llm_request_timeout_budget_ms

Validation step:

Send one synthetic request with a minimal messages array and the smallest acceptable completion budget for your use case. Confirm that the request is accepted according to the fields documented in the CometAPI chat completions API reference.

2. Response shape signal

A healthy response should satisfy the shape your application actually consumes. If your application reads choices[0].message.content, then monitor that exact path.

Check for:

• response is parseable JSON for non-streaming calls
• choices exists and is a non-empty array when a completion is expected
• first choice contains the message or delta structure your client expects
• finish reason is present when documented
• usage fields are present if your budgeting or reconciliation depends on them
• response model value is captured for audit

Suggested counters:

• llm_response_schema_valid_total
• llm_response_schema_invalid_total
• llm_response_missing_choices_total
• llm_response_empty_content_total
• llm_response_missing_usage_total

Validation step:

Run a probe that asks for a short deterministic answer, such as “Reply with exactly: pong.” Do not assert the text as a hard guarantee unless the model and sampling controls support it. Instead, assert that the response has the required shape and contains non-empty assistant output.

3. Error contract signal

Operators need to know whether an error should trigger retry, fallback, traffic shedding, or configuration repair.

Classify errors into:

• authentication or authorization failures
• malformed request failures
• quota or rate-limit failures
• timeout failures
• upstream 5xx failures
• response parse failures
• application-level validation failures after HTTP 200

Example routing:

Validation step:

In a non-production environment, send a controlled request with a deliberately invalid model name or malformed payload, if safe for your account. Confirm that your client records the status code, redacted error body shape, retry decision, and owning runbook.

4. Latency and timeout signal

Latency monitoring should be split into phases if your client can measure them:

• DNS/connect/TLS time
• time to first byte
• time to first token for streaming
• full response time
• client-side timeout
• retry-added latency

Suggested metrics:

• llm_latency_ms
• llm_time_to_first_byte_ms
• llm_time_to_first_token_ms
• llm_completion_duration_ms
• llm_client_timeout_total

Validation step:

Set one synthetic probe with a short prompt and one with a slightly larger prompt. Compare p50, p95, and timeout rate by prompt size. Treat any threshold, such as “p95 under 10 seconds,” as an internal SLO candidate, not a universal CometAPI guarantee.

5. Usage and budget signal

If your system enforces token budgets, monitor the fields you actually use for budget decisions. Many clients depend on prompt token count, completion token count, and total token count when present.

Recommended checks:

• usage field exists when expected
• total token count is non-negative
• total token count is greater than or equal to prompt token count when both are present
• completion token count is within the caller’s configured maximum
• usage is attached to the correct request ID or trace ID

Validation step:

Issue a known small prompt and confirm that usage fields, if documented and returned, are captured into your telemetry pipeline. Then compare a sample of application logs with downstream accounting. Do not treat usage fields as final billing records unless your CometAPI commercial documentation says so.

Sanitized curl-style validation example

Use this as a template for a synthetic contract probe. Replace placeholders with your actual secret management and model configuration. Keep the prompt non-sensitive.

curl -sS -X POST "https://YOUR_COMETAPI_BASE_URL/v1/chat/completions" \
  -H "Authorization: Bearer ${COMETAPI_API_KEY}" \
  -H "Content-Type: application/json" \
  -H "X-Request-Source: synthetic-contract-probe" \
  -d '{
    "model": "YOUR_VERIFIED_MODEL_ID",
    "messages": [
      {
        "role": "system",
        "content": "You are responding to a production API contract probe."
      },
      {
        "role": "user",
        "content": "Reply with one short sentence confirming the API response is usable."
      }
    ],
    "stream": false
  }'

Expected validation outcomes:

• HTTP status is successful.
• Response body is valid JSON.
• Response contains a non-empty choices array in the documented shape.
• Assistant output is present where your client expects it.
• Usage fields are recorded if the documented endpoint returns them.
• No prompt text, API key, or full response body is emitted to high-cardinality metrics.

Before using this in production, verify the base URL, endpoint path, header requirements, field names, and model identifier against the CometAPI API documentation.

Practical validation workflow

Step 1: Capture the documented contract

Create a small contract file in your repo that records:

• endpoint path
• method
• required headers
• minimum request body
• response paths your app reads
• retryable status codes
• non-retryable status codes
• timeout budget
• streaming vs non-streaming behavior
• usage fields your budget logic reads

Link that file to the CometAPI API documentation URL and include the review date.

Step 2: Add pre-deploy contract tests

Run these before deploying changes to the LLM client:

1. Build a request from production configuration with a test prompt.
2. Redact secrets and prompt content.
3. Validate the request against your stored contract.
4. Send the request in a safe environment.
5. Validate response shape.
6. Confirm retry classification for one controlled failure mode.
7. Confirm telemetry fields are emitted.

Step 3: Add production synthetic probes

Run probes at a low, controlled interval. Keep them separate from user traffic with a header, request tag, or metadata field if your gateway supports it.

Probe checklist:

• non-streaming success probe
• streaming success probe, if your application uses streaming
• invalid-request probe in non-production only
• timeout-boundary probe, if safe and cost-controlled
• usage-field capture probe, if token budgeting depends on usage

Step 4: Monitor contract drift separately from availability

Create a dashboard section named “contract health,” not just “provider health.”

Include:

• schema-valid rate
• missing required response paths
• parse failures
• auth failures after deploy
• rate-limit or quota-like responses
• client timeout rate
• fallback activation rate
• retry success after first failure
• usage-field availability
• response model distribution

This makes it easier to distinguish a vendor outage from a client-side contract mismatch.

Step 5: Review after provider documentation changes

Whenever the CometAPI API documentation, your SDK, or gateway config changes, repeat the validation workflow. A doc change does not automatically mean breaking behavior, but it is a good trigger for a contract review.

FAQ

Is an HTTP 200 enough to mark the API healthy?

No. For chat completions, HTTP 200 only says the transport request succeeded. Your application also needs the response fields it consumes, such as choices, assistant content, finish reason, and usage fields if your budget logic depends on them.

Should schema failures trigger fallback?

Usually yes, if the user request can still be served safely by another configured provider or model. But fallback should respect retry budgets, data policy, and product behavior. Avoid unlimited retries across providers.

Can I use the curl probe as a production health check?

Yes, if you make it low-volume, non-sensitive, observable, and cost-controlled. Mark it as synthetic traffic and avoid prompts that expose customer data.

Should I alert on missing usage fields?

Alert only if usage fields are part of your documented and validated contract. If usage fields are optional or unavailable for a mode such as streaming, record the condition separately and avoid paging unless it breaks budgeting or reconciliation.

What should I do before enforcing rate-limit alerts?

Confirm whether CometAPI documents rate-limit headers or quota behavior for your account. If not, alert on observed 429-like responses and customer impact, but avoid assuming exact reset semantics.

How often should this contract be reviewed?

Review it when you change client code, gateway routing, model configuration, auth handling, streaming mode, or retry policy. Also review it when the CometAPI API documentation changes or after any production incident involving chat completions.

Sources checked