El Developer Agéntico

English · Español

Build your first agent. Develop it with specifications, tests and clear limits.

An open book by Bezael Pérez · Dominicode. Edition 1.1, September 2026.

19 chapters, a quick-start path and eight appendices. Equivalent code in Python and TypeScript. Text under CC BY-SA 4.0; code under MIT.

The book is written in Spanish. All the code, including identifiers, comments, messages, prompts and sample data, is in English.

Start with a result

From the repository root, pick one:

python examples/python/agent.py --demo

node examples/typescript/agent.ts --demo

The demo uses local data and simulated model responses. It generates PRIORITIES.md offline, with no API keys and no cost. It needs Python 3.10+ or Node.js 24. If the report already exists, the demo keeps it and fails: rename it before running again.

Read Empieza aquí (the quick-start path), the table of contents and the project instructions. Live mode uses an SDK and API usage billed separately from the ebook.

What's inside

• The loop: models, tools, context and memory.
• Observability: traces and spans to know what your agent actually did.
• RAG, patterns, multi-agent systems and MCP.
• Permissions, evaluation, production failures and costs.
• A runnable project with tests, plus five reference designs to adapt.
• Two workshops to specify and verify a change with Claude Code.
• Contract Review Method: Contract → Lane → Verdict, with a worked case and a review template.

Conceptual snippets explain individual pieces; the runnable programs and their tests live in examples/. The business recipes are reference designs, not five deployed applications.

Verify the examples

python -m unittest discover -s examples/python -p "test_*.py"
node --test examples/typescript/agent.test.ts

To type-check, install the TypeScript example's dependencies and run its typecheck script:

npm ci --prefix examples/typescript
npm run typecheck --prefix examples/typescript

The CI template is in examples/workshop/verify.yml.example. Read its instructions before enabling it in your copy. Offline tests do not certify a real API run.

Build the PDF and EPUB

Requirements: Node.js 24, npm, Pandoc 3.9 and Python 3.10+ for the checks. Installing Puppeteer downloads Chromium; if your environment already manages it, see Puppeteer's official configuration.

npm ci
npm run check
npm run build

Set PANDOC to point to the executable if it isn't on your PATH. The build uses system fonts and downloads no web fonts, so the output may vary slightly between systems.

If your PDF viewer locks an open file, set BOOK_PDF_SUFFIX=-contract-review to write a copy with that suffix. The EPUB keeps its usual name.

Outputs:

• output/pdf/el-developer-agentico.pdf
• output/epub/el-developer-agentico.epub
• output/pdf/guia-desarrollo-agentico.pdf: a short excerpt built from the same source.
• output/html/: previews for inspecting the layout.

The reading order and appendices are defined once, in manuscript/Book.txt.

Share and contribute

The full text can be read and redistributed under its license. The PDF/EPUB download by email gives you a ready-to-read edition and optional updates; it doesn't make the content exclusive.

See the text license, code license, contributing guide and changelog.