← Volver a las guías

Build a Testable Claude Code Agent: 2026 Guide

Building a coding agent with Claude Code in 2026 starts with a practical distinction: generating a patch is not the same as delivering a verified change. Claude Code already provides file tools, command execution, and an agent loop; the Agent SDK exposes that infrastructure programmatically. Your job is to define the task, constrain execution, and independently validate the result. ([code.claude.com](https://code.claude.com/docs/en/headless))

1. Start with one measurable task

Choose a small repository task: fix an empty-input parser bug, add a missing validation check, or update a failing unit test. Write acceptance criteria before launching the agent. For example: empty input returns an empty array, existing cases remain unchanged, and no dependency changes are permitted.

Install Claude Code using the official installation instructions, then create a dedicated Git branch or worktree. Run the existing test suite yourself and record the baseline. This separates pre-existing failures from regressions introduced by the agent. ([code.claude.com](https://code.claude.com/docs/en/setup))

2. Connect 59API and verify routing

59API offers low-cost, pay-as-you-go access without requiring a monthly subscription. Its stated offering includes official-quality model capability, Claude Code compatibility, and referral rebates. That makes it worth evaluating for experiments where usage varies between quiet days and intensive debugging sessions. Compare actual token bills rather than assuming every route has identical pricing. ([59api.com](https://59api.com/))

• Set ANTHROPIC_BASE_URL to 59API’s documented API endpoint.
• Set ANTHROPIC_AUTH_TOKEN to your 59API key through a local environment or CI secret store.
• For a concrete starting point, select Claude Sonnet 5.5 and copy its API identifier from the provider rather than guessing a slug.
• Launch Claude Code from the configured shell, send a small request, and inspect /status to confirm the endpoint and credential source.

59API documents the endpoint-and-token setup; Anthropic documents how to verify gateway routing. Keep credentials out of committed project settings. Also distinguish API formats: OpenAI SDK compatibility alone does not establish Claude Code compatibility; use the relay’s Claude Code configuration. ([59api.com](https://59api.com/))

3. Give the agent a repository contract

Create a concise CLAUDE.md at the repository root. Include the relevant directory map, exact test and lint commands, coding conventions, and completion requirements. Claude Code loads these files as persistent project instructions. ([code.claude.com](https://code.claude.com/docs/en/memory))

• Scope: modify the parser and its tests, not unrelated modules.
• Verification: add a regression test and run the relevant suite.
• Reporting: list changed files, executed commands, and unresolved failures.

Treat these instructions as guidance, not access control. Enforce restrictions through permissions and operating-system isolation; a sentence saying “never read secrets” is not a security boundary. ([code.claude.com](https://code.claude.com/docs/en/permissions))

4. Turn the workflow into a bounded worker

First complete one supervised run. Once its commands and permissions are understood, automate with claude -p. For an audited npm project, a starting command is:

claude -p 'Fix the empty-input parser bug, add regression tests, run npm test, and summarize changes.' --allowedTools 'Read,Glob,Grep,Edit,Write,Bash(npm test *)' --permission-mode dontAsk --max-turns 12 --max-budget-usd 2 --output-format json

The tool list pre-approves matching actions; it is not an exhaustive security sandbox. The dontAsk mode denies actions that would otherwise require approval. Test scripts themselves execute code, so audit them before granting unattended access. ([code.claude.com](https://code.claude.com/docs/en/permissions))

Have your wrapper set the working directory, enforce a wall-clock timeout, capture stdout and stderr, and check the exit status. Parse the JSON result instead of scraping terminal prose. For schema-constrained reports, add --json-schema and verify that structured output exists before consuming it. ([code.claude.com](https://code.claude.com/docs/en/headless))

5. Verify independently and measure real cost

Run unattended jobs in disposable containers without production credentials. Restrict network access, inspect repository hooks and external integrations, and require human review before merging. Claude Code’s security guidance recommends isolation and reviewing proposed changes. ([code.claude.com](https://code.claude.com/docs/en/security))

After execution, independently rerun tests and linting, inspect the diff, and reject unrelated edits. Track accepted fixes, regressions, runtime, and provider-billed cost. The CLI budget flag uses an estimate that can differ from the relay’s bill and can overshoot; it is not a guaranteed spending ceiling. ([code.claude.com](https://code.claude.com/docs/en/cli-reference))

If you want to test this workflow economically, sign up for 59API and begin with one small, measurable task. Expand autonomy only after the agent consistently produces reviewable, verified changes.

Precios · Docs