Declare MCP Tool Manifests Before Coding Agents Call CometAPI

Last reviewed: 2026-07-21

Direct answer

Before a coding agent workflow calls CometAPI with tool-enabled requests, declare and inspect the MCP tool manifest first. The manifest should make each exposed tool understandable by name, description, input schema, and, when available, output schema. Then map the request to the CometAPI endpoint family you plan to use, run one small success case, run one controlled failure case, and record only the contract evidence you can verify.

Use this sequence:

1. Setup assumptions: the MCP server exposes only the tools intended for the workflow; credentials are stored outside the prompt; the CometAPI base URL and endpoint family are selected from the current CometAPI documentation; the coding agent has no write or network permission beyond the intended test.
2. Happy-path request plan: list tools from the MCP server, choose one non-destructive tool, send a minimal request through the selected CometAPI endpoint family, and confirm that the response shape contains the expected top-level status and output fields documented for that endpoint.
3. Error-path check: repeat the request with one intentionally missing required field or an invalid placeholder credential such as <API_KEY_PLACEHOLDER> and confirm the failure is handled without retry loops or hidden tool calls.
4. Minimum assertions: record the MCP tool name, declared input schema, selected endpoint family, HTTP status class, whether output was present, whether tool calls were expected, and whether the request stayed inside the approved tool list.
5. Pass/fail logging fields: run_id, tool_name, endpoint_family, request_fixture_id, expected_path, observed_status_class, tool_call_allowed, contract_result, evidence_links, and operator_note.
6. What not to assert: do not claim model availability, price, billing impact, latency, uptime, quota, or production readiness from this smoke test alone.

For adjacent gateway setup checks, see Route Coding Agent Model Calls Without Endpoint Drift and Preflight Request Fixtures for Coding Agents Using CometAPI . To start a CometAPI account path from this guide, use Start with CometAPI .

Who this is for

This guide is for engineers who let coding agents call model gateways, run tool-enabled review loops, or test MCP-connected workflows. It is especially useful when a repository already has several gateway-related checks and the next failure mode is not the API call itself, but an undeclared or over-broad tool surface.

Use it when a coding agent can reach an MCP server, when a gateway client can send Chat Completions or Responses-style requests, and when the team needs a small, repeatable check before giving an agent a larger task. It also fits teams that already separate setup, request fixtures, execution logs, and handoff notes. If your current concern is permission scope rather than model routing, pair this guide with Set Safe Permission and Secret Boundaries for Coding Agents .

Key takeaways

• MCP tools are intended to be discoverable by clients through a declared tool list, not guessed from prompts.
• Tool definitions should be treated as part of the request contract because they describe names, descriptions, input schemas, and optional output schemas.
• CometAPI endpoint-family checks should stay narrow: verify the documented endpoint path and response area you use, then leave commercial and account-specific assumptions out of the smoke test.
• A useful record proves what was allowed, what was called, and what was observed without storing credentials or full model output.
• Tool-result errors and protocol errors should be logged separately, because they point to different repair paths.

Sanitized log record:

{
  "run_id": "gateway-smoke-YYYYMMDD-001",
  "tool_name": "example_non_destructive_tool",
  "endpoint_family": "responses_or_chat",
  "request_fixture_id": "fixture-minimal-tool-call",
  "expected_path": "documented_endpoint_family",
  "observed_status_class": "2xx_or_4xx",
  "tool_call_allowed": true,
  "contract_result": "pass_or_fail",
  "evidence_links": ["https://modelcontextprotocol.io/specification/2025-06-18/server/tools"],
  "operator_note": "placeholder only; no prompt, credential, price, limit, or full response stored"
}

The point of the record is not to prove that every future request will work. It proves that one named tool, one fixture, and one endpoint family were checked in a way another engineer can inspect. That is enough to decide whether the coding agent can proceed to a limited workflow, needs a corrected manifest, or should stop until the gateway setup is clarified.

Sources checked

• Official source evidence 1 - accessed 2026-07-21; purpose: verify source-backed claims for this guide.

• Official source evidence 2 - accessed 2026-07-21; purpose: verify source-backed claims for this guide.

• Official source evidence 3 - accessed 2026-07-21; purpose: verify source-backed claims for this guide.

• CometAPI Responses reference - accessed 2026-07-21; purpose: verify the Responses endpoint family and its documented response and tool-related request areas.

• CometAPI Chat Completions reference - accessed 2026-07-21; purpose: verify the chat endpoint family, OpenAI-compatible base URL framing, and request/response boundary caveats.

• CometAPI models overview - accessed 2026-07-21; purpose: verify that model selection should be checked against the current model catalog instead of hard-coded from memory.

• CometAPI help center - accessed 2026-07-21; purpose: verify the support reference path for account-specific limits, errors, maintenance, privacy, or unclear gateway behavior.

Contract details to verify

A practical check should keep those areas separate. The MCP manifest tells you what tools the agent may see and call. The CometAPI endpoint page tells you which HTTP path and response family you are exercising. The model catalog tells you where model identity and capability checks belong. The help page tells you where to send questions that depend on account state, maintenance, limits, or private billing context. Mixing those into one broad assertion makes the result harder to trust.

Failure modes

• Evidence gap: the agent cannot inspect the failing log, source page, pull request, or local command output. The safe action is to stop and record the missing evidence instead of guessing.
• Scope drift: the agent edits files that are not connected to the observed failure. Keep the repair tied to the failing signal and leave unrelated cleanup for a separate task.
• Environment mismatch: the local check uses different versions, credentials, feature flags, or runtime settings than the hosted path. Record the mismatch before treating the result as proof.
• Unreviewed fallback: the agent changes models, endpoints, permissions, or retry behavior to make a run pass without preserving the review boundary. Treat access and provider failures as operational blockers, not topic failures.
• Weak handoff: the final note says the issue is fixed but omits the command, result, changed files, and remaining uncertainty. That makes the next operator repeat the investigation.
• Over-broad tool list: the MCP server exposes a tool that is unrelated to the workflow, destructive by default, or described too vaguely for the agent to reason about. Remove or isolate that tool before the gateway call.
• Schema mismatch: the fixture sends arguments that do not match the declared input schema, or the tool returns structured content that is not checked against the available output schema. Treat that as a contract failure, not as a model quality issue.
• Endpoint drift: the client claims to test one CometAPI endpoint family while the request fixture points at another. Fix the fixture naming, base URL, and request path before interpreting the result.

Reader next step

Create a one-page manifest check for your next coding agent gateway run. Put the MCP tool name, description, input schema summary, selected CometAPI endpoint family, credential storage assumption, happy-path fixture, error-path fixture, and pass/fail log fields in the same note. Then run only the smallest non-destructive request that proves the declared tool and endpoint family match your intended workflow.

If the note exposes a missing schema, unclear endpoint family, unsupported model choice, or account-specific question, do not expand the agent task yet. Correct the manifest or check the current CometAPI documentation first. For a related evidence pattern, use Validate CometAPI Source Evidence Before Your Agent Tutorial Ships before you turn the fixture into a repeatable team runbook.

FAQ

Why declare MCP tools before the first gateway call?

Because the tool list is the boundary the coding agent can reason over. If the list is missing, stale, or too broad, a successful model response can still be operationally unsafe. The agent may appear to answer correctly while relying on a tool that was never meant to be exposed.

Should the smoke test prove the gateway is production ready?

No. It should prove that the selected tool and endpoint-family contract behaves as expected for a small fixture. Production readiness also needs permission review, monitoring, cost controls, support handling, and account-specific limits.

Can I hard-code model IDs in the guide or fixture?

Only if the current model documentation or account-visible configuration supports that exact choice at the time you run the check. Otherwise, keep the fixture model value configurable and record that model selection was checked separately.

What should be excluded from the log record?

Exclude credentials, full prompts, full responses, prices, limits, uptime claims, and private account details. Keep only enough evidence to reproduce the contract check: tool name, schema summary, endpoint family, status class, fixture ID, and the source links used.

What is a good first error-path check?

Use a deliberately invalid placeholder credential or a fixture with one missing required argument. The expected outcome is a bounded failure record, not a successful model answer. If the client retries repeatedly, calls a different tool, or hides the failing response, stop and fix the workflow boundary.

When should I contact support instead of changing code?

Use the current CometAPI support path when the behavior depends on account limits, maintenance, access, privacy logging, or billing details that are not proven by the public endpoint documentation. Do not encode private assumptions into a coding agent fixture.