compare_monsters

Compare D&D 5e monsters side by side to analyze AC, HP, abilities, resistances, immunities, and special actions for encounter planning.

Instructions

Compare 2-3 D&D 5e monsters side by side. Shows AC, HP, ability scores, speeds, resistances, immunities, actions, and special abilities.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`monster_names`	Yes	Names of 2-3 monsters to compare

Implementation Reference

src/tools/compare-monsters.ts:83-175 (handler)

The async handler function for the 'compare_monsters' tool, which processes input monster names, retrieves data from the database, formats the comparison table in Markdown, and returns it.

  async ({ monster_names }) => {
    const monsters: MonsterRow[] = [];
    const notFound: string[] = [];

    for (const name of monster_names) {
      const monster = getMonsterByName(db, name);
      if (monster) {
        monsters.push(monster);
      } else {
        notFound.push(name);
      }
    }

    if (notFound.length > 0) {
      return {
        content: [
          {
            type: 'text' as const,
            text: `Monster(s) not found: ${notFound.join(', ')}. Use the search_monsters tool first to find the exact name.`,
          },
        ],
        isError: true,
      };
    }

    const lines: string[] = [];
    lines.push('# Monster Comparison');
    lines.push('');

    // Separator helper for table
    const sep = monsters.map(() => '---').join(' | ');
    const header = monsters.map((m) => `**${m.name}**`).join(' | ');

    lines.push(`| Stat | ${header} |`);
    lines.push(`|------|${sep}|`);

    // Basic info
    lines.push(`| Size | ${monsters.map((m) => m.size).join(' | ')} |`);
    lines.push(`| Type | ${monsters.map((m) => {
      const sub = m.subtype ? ` (${m.subtype})` : '';
      return `${m.type}${sub}`;
    }).join(' | ')} |`);
    lines.push(`| Alignment | ${monsters.map((m) => m.alignment).join(' | ')} |`);

    // Combat stats
    lines.push(`| AC | ${monsters.map((m) => {
      return m.ac_type ? `${m.ac} (${m.ac_type})` : `${m.ac}`;
    }).join(' | ')} |`);
    lines.push(`| HP | ${monsters.map((m) => `${m.hp} (${m.hit_dice})`).join(' | ')} |`);
    lines.push(`| Speed | ${monsters.map((m) => formatSpeed(m.speed)).join(' | ')} |`);
    lines.push(`| CR | ${monsters.map((m) => {
      const xp = m.xp || getXpForCr(m.cr);
      return `${m.cr} (${xp.toLocaleString()} XP)`;
    }).join(' | ')} |`);
    lines.push(`| Prof. Bonus | ${monsters.map((m) => m.proficiency_bonus ? `+${m.proficiency_bonus}` : '—').join(' | ')} |`);

    // Ability scores
    lines.push(`| STR | ${monsters.map((m) => formatScore(m.str)).join(' | ')} |`);
    lines.push(`| DEX | ${monsters.map((m) => formatScore(m.dex)).join(' | ')} |`);
    lines.push(`| CON | ${monsters.map((m) => formatScore(m.con)).join(' | ')} |`);
    lines.push(`| INT | ${monsters.map((m) => formatScore(m.int)).join(' | ')} |`);
    lines.push(`| WIS | ${monsters.map((m) => formatScore(m.wis)).join(' | ')} |`);
    lines.push(`| CHA | ${monsters.map((m) => formatScore(m.cha)).join(' | ')} |`);

    // Defenses
    lines.push(`| Resistances | ${monsters.map((m) => m.resistances ?? '—').join(' | ')} |`);
    lines.push(`| Immunities | ${monsters.map((m) => m.immunities ?? '—').join(' | ')} |`);
    lines.push(`| Vulnerabilities | ${monsters.map((m) => m.vulnerabilities ?? '—').join(' | ')} |`);
    lines.push(`| Condition Immunities | ${monsters.map((m) => m.condition_immunities ?? '—').join(' | ')} |`);

    // Senses & languages
    lines.push(`| Senses | ${monsters.map((m) => m.senses ?? '—').join(' | ')} |`);
    lines.push(`| Languages | ${monsters.map((m) => m.languages ?? '—').join(' | ')} |`);
    lines.push('');

    // Detailed sections
    const traitSection = formatAbilitiesSection('Traits', monsters, 'traits');
    if (traitSection) lines.push(traitSection);

    const actionSection = formatAbilitiesSection('Actions', monsters, 'actions');
    if (actionSection) lines.push(actionSection);

    const reactionSection = formatAbilitiesSection('Reactions', monsters, 'reactions');
    if (reactionSection) lines.push(reactionSection);

    const legendarySection = formatAbilitiesSection('Legendary Actions', monsters, 'legendary_actions');
    if (legendarySection) lines.push(legendarySection);

    return {
      content: [{ type: 'text' as const, text: lines.join('\n') }],
    };
  },
);

src/tools/compare-monsters.ts:70-82 (schema)

The definition and input schema (zod validation) for the 'compare_monsters' tool.

server.registerTool(
  'compare_monsters',
  {
    description:
      'Compare 2-3 D&D 5e monsters side by side. Shows AC, HP, ability scores, speeds, resistances, immunities, actions, and special abilities.',
    inputSchema: {
      monster_names: z
        .array(z.string())
        .min(2)
        .max(3)
        .describe('Names of 2-3 monsters to compare'),
    },
  },

src/tools/compare-monsters.ts:66-176 (registration)

Function used to register the 'compare_monsters' tool with the McpServer.

export function registerCompareMonsters(
  server: McpServer,
  db: Database.Database,
): void {
  server.registerTool(
    'compare_monsters',
    {
      description:
        'Compare 2-3 D&D 5e monsters side by side. Shows AC, HP, ability scores, speeds, resistances, immunities, actions, and special abilities.',
      inputSchema: {
        monster_names: z
          .array(z.string())
          .min(2)
          .max(3)
          .describe('Names of 2-3 monsters to compare'),
      },
    },
    async ({ monster_names }) => {
      const monsters: MonsterRow[] = [];
      const notFound: string[] = [];

      for (const name of monster_names) {
        const monster = getMonsterByName(db, name);
        if (monster) {
          monsters.push(monster);
        } else {
          notFound.push(name);
        }
      }

      if (notFound.length > 0) {
        return {
          content: [
            {
              type: 'text' as const,
              text: `Monster(s) not found: ${notFound.join(', ')}. Use the search_monsters tool first to find the exact name.`,
            },
          ],
          isError: true,
        };
      }

      const lines: string[] = [];
      lines.push('# Monster Comparison');
      lines.push('');

      // Separator helper for table
      const sep = monsters.map(() => '---').join(' | ');
      const header = monsters.map((m) => `**${m.name}**`).join(' | ');

      lines.push(`| Stat | ${header} |`);
      lines.push(`|------|${sep}|`);

      // Basic info
      lines.push(`| Size | ${monsters.map((m) => m.size).join(' | ')} |`);
      lines.push(`| Type | ${monsters.map((m) => {
        const sub = m.subtype ? ` (${m.subtype})` : '';
        return `${m.type}${sub}`;
      }).join(' | ')} |`);
      lines.push(`| Alignment | ${monsters.map((m) => m.alignment).join(' | ')} |`);

      // Combat stats
      lines.push(`| AC | ${monsters.map((m) => {
        return m.ac_type ? `${m.ac} (${m.ac_type})` : `${m.ac}`;
      }).join(' | ')} |`);
      lines.push(`| HP | ${monsters.map((m) => `${m.hp} (${m.hit_dice})`).join(' | ')} |`);
      lines.push(`| Speed | ${monsters.map((m) => formatSpeed(m.speed)).join(' | ')} |`);
      lines.push(`| CR | ${monsters.map((m) => {
        const xp = m.xp || getXpForCr(m.cr);
        return `${m.cr} (${xp.toLocaleString()} XP)`;
      }).join(' | ')} |`);
      lines.push(`| Prof. Bonus | ${monsters.map((m) => m.proficiency_bonus ? `+${m.proficiency_bonus}` : '—').join(' | ')} |`);

      // Ability scores
      lines.push(`| STR | ${monsters.map((m) => formatScore(m.str)).join(' | ')} |`);
      lines.push(`| DEX | ${monsters.map((m) => formatScore(m.dex)).join(' | ')} |`);
      lines.push(`| CON | ${monsters.map((m) => formatScore(m.con)).join(' | ')} |`);
      lines.push(`| INT | ${monsters.map((m) => formatScore(m.int)).join(' | ')} |`);
      lines.push(`| WIS | ${monsters.map((m) => formatScore(m.wis)).join(' | ')} |`);
      lines.push(`| CHA | ${monsters.map((m) => formatScore(m.cha)).join(' | ')} |`);

      // Defenses
      lines.push(`| Resistances | ${monsters.map((m) => m.resistances ?? '—').join(' | ')} |`);
      lines.push(`| Immunities | ${monsters.map((m) => m.immunities ?? '—').join(' | ')} |`);
      lines.push(`| Vulnerabilities | ${monsters.map((m) => m.vulnerabilities ?? '—').join(' | ')} |`);
      lines.push(`| Condition Immunities | ${monsters.map((m) => m.condition_immunities ?? '—').join(' | ')} |`);

      // Senses & languages
      lines.push(`| Senses | ${monsters.map((m) => m.senses ?? '—').join(' | ')} |`);
      lines.push(`| Languages | ${monsters.map((m) => m.languages ?? '—').join(' | ')} |`);
      lines.push('');

      // Detailed sections
      const traitSection = formatAbilitiesSection('Traits', monsters, 'traits');
      if (traitSection) lines.push(traitSection);

      const actionSection = formatAbilitiesSection('Actions', monsters, 'actions');
      if (actionSection) lines.push(actionSection);

      const reactionSection = formatAbilitiesSection('Reactions', monsters, 'reactions');
      if (reactionSection) lines.push(reactionSection);

      const legendarySection = formatAbilitiesSection('Legendary Actions', monsters, 'legendary_actions');
      if (legendarySection) lines.push(legendarySection);

      return {
        content: [{ type: 'text' as const, text: lines.join('\n') }],
      };
    },
  );
}

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